Freshwater Fish of Bulgaria

Maria Karapetkova, Mladen ¥ivkov, and Koyka Alexandrova-Kelomanov

Summary

The contemporary Bulgarian ichthyofauna consists of 207 species and subspecies, 122 of which inhabit fresh and brackish waters - rivers, wetlands and natural and man-made lakes. In this report, species diversity is discussed according to the watershed and type of water basin.

I. The Danube River Watershed

The fish of the Bulgarian section of the Danube River and its tributaries constitute a unified ichthyo-complex containing 77 species and subspecies. Twelve taxa of typical Danubian fish - Hucho hucho, Alosa caspia nordmani, some of the Acipenseridae species, etc. - have never been found in the tributaries. Conversely, 10 cold-loving taxa (mostly species of Salmo, Cobitis, Cottus, etc.) inhabit only the upper parts of the middle stretches of the tributaries. Within the ichthyocomplex as a whole, the most abundantly represented family is Cyprinidae (31), followed by Percidae (8), Cobitidae (7), and Gobiidae (7). This watershed contains 11 species listed in the Bulgarian Red Data Book, as well as other species that are rare or limited in distribution and that require protection. Sabanejwia bulgarica and Cottus gobio heasmusi are endemic forms.

II. The Black Sea Watershed

The ichthyofauna of the Black Sea rivers includes 77 species and subspecies. These are divided into two groups: permanent residents of the rivers (39) and temporary immigrants from the Black Sea or the lakes (38). The permanent residents are represented most abundantly by Cyprinidae species (21), followed by Gobiidae (5) and diverse representatives of different families. The relative importance of the Gobiidae is increased by the presence of other species that enter the rivers occasionally. The other temporary residents are sea species.

The ichthyofauna of the Bulgarian seaside lakes consists of a total of 79 species and subspecies. Forty-three are permanent residents and 36 temporary (either occasional or regular) residents. The predominance of freshwater or Black Sea species fluctuates depending on the hydrologic regime and saprobic condition of the lake waters.

The unique character of the Black Sea ichthyo-complex is due to the combination of original freshwater species (37 in all, including 21 relict species - 14 Ponto Caspian and 7 Boreal Atlantic) and Mediterranean immigrants (43 species). Endemic forms are Alosa caspia bulgarica and Cobitis peshevi. The ichthyocomplex requires strong protection.

III. The Aegean Sea Watershed

The ichthyofauna of the rivers in southern Bulgaria comprises 50 species and subspecies. The Cyprinidae family, represented by 23 species, is definitely predominant, followed by the Cobitidae (6) and Salmonidae (3). The other families are represented by single species. In addition to those species that are listed in the Bulgarian Red Data Book, the rivers in this region contain 5 species with limited ranges or small populations, and others that are in the process of acclimatizing being introduced. The Aegean watershed is famous for its many endemic forms, which are also characteristic for the Balkan peninsula. These are: Vimba melanops, Cobitis peshevi, Rutilus rutilus mariza, Barbus cyclolepis cyclolepis, Chondrostoma nasus vardarenses, Sabanejwia aurata balcanica, and Noemacheilus angorae bureschi. In order to preserve Vimba melanops and Barbus cyclolepis, which naturally inhabit the Maritsa River, measures need to be taken to protect key habitats on the lower course of the Vatch River and on the Shirokolashka River.

IV. Standing Waters

The ichthyofauna of the mountain lakes includes 15 species, all of them belonging to Salmonidae and Cyprinidae. The ichthyofauna of the large and small reservoirs and fish farms has developed as a result of intensive importation of economically valuable stocking material as well as the adaptation of genetic stock from the local aboriginal fauna. Cyprinidae species predominate.

As a result of this general survey of the Bulgarian freshwater and brackish water ichthyofauna, we have revised upwards our figures on species composition.

This is due in part to the research methods employed, but also to the intensive importation of new species and natural expansion in the ranges of other species. Simultaneously, however, populations of the dominant species have undergone changes, resulting in a definite decline in fishstocks. We require a comprehensive program to preserve the genofund and to increase the fishstock.

Overview of the Bulgarian Freshwater Ichthyofauna

The contemporary Bulgarian ichthyofauna consists of 207 species and subspecies, 122 of which inhabit fresh and brackish waters - rivers, wetlands and natural and man-made lakes. The formation of the freshwater ichthyocomplex of Bulgaria's northern rivers and watersheds up to the Stara Planina Mountains has been influenced by its direct connection to the Danube River, which possesses the richest ichthyofauna in Europe. The other rivers and lakes of the Black Sea watershed area are inhabited by freshwater species (including Ponto-Caspian and Boreal-Atlantic relicts) and Mediterranean immigrants. Some Danubian species also occur, the number diminishing from north to south. The rivers and other water bodies of southern Bulgaria that belong to the Aegean watershed contain species that are specific to that region as well as some Danubian and Black Sea species.

Information on the diversity of the Bulgarian freshwater ichthyofauna will be presented according to the different watersheds due to their specific characteristics.

The Danube River Watershed

The Bulgarian section of the Danube River and its bulgarian tributaries are inhabited by a single and unified ichthyocomplex that includes 74 species and subspecies. Thirteen species are found only in the Danube itself. Ten others are found only in the tributaries: Salmo trutta fario, S. gairdneri irideus, Phoxinus phoxinus, Barbus meridionalis petenyi, Cobitis aurata bulgarica, C. aurata balcanica, C. elongata, and Cottus gobio, as well as Coregonus lavaretus and C. peled, which are being introduced to the waters near the Iskar Dam. These are exclusively cold-water species, and are adapted to the conditions of the mountain areas. Some are found in the rivers of the plain as well, but never reach the Danube River.

The Bulgarian Section of the Danube river

The Bulgarian section of the Danube River lies wholly in the lower course of the river between its 845th and 375th kilometers. Out of a total of 83 species inhabiting the entire Danube, 65 are found in the Bulgarian section. A review of the ichthyological scientific literature shows that, up until now, 64 species had been found (Kovatchev, 1909, 1910, 1923; Drensky, 1923, 1926, 1928, 1930, 1935, 1941, 1943, 1948, 1951; Morov, 1931; Shishkov, 1935, 1937a, 1937b, 1938, 1940a, 1940b, 1941, 1943; Kolarov, 1960, 1965a, 1964b, 1972, 1982, 1983, 1989, 1991; Ivanov, 1959, 1962, 1970; Rusev, 1963; Undjijan, 1964; Marinov, 1966, 1978; Sivkov, 1979, 1980, 1985, 1986, 1987a, 1987b, 1988a, 1988b, 1989a, 1989b, 1991a, 1991b; Sivkov and Dobrovolov, 1986).

Appendix 1 lists the fish species found in the Bulgarian Danube. The total number of fish species inhabiting the Bulgarian fresh and sea waters is over 200. Thus, about a quarter of them occur in the Bulgarian section of the Danube. The Danube's share of Bulgaria's strictly freshwater ichthyofauna is even larger - about 2/3 of all the species occur there. This rich diversity of fish species is due to the Danube's great volume of water, its varied ecological conditions, and its relative proximity to Siberia, where a majority of the European freshwater fauna originated. The Danube is the only large river that flows across most of Europe, connecting the central and western parts of the continent with the eastern countries. The Danube thus has a significant role to play in preserving the fish genetic diversity not only of Bulgaria but of the whole of Europe.

The Danube basin, including its Bulgarian section, is a species formation center. Endemic fish such as Sabanejwia bulgarica, Gymnocephalus schraetzer, G. baloni, and Hucho hucho can be found there. In addition to species that are included in the Bulgarian Red Data Book, the Bulgarian Danube contains species that are rarely caught and considered limited in number - members of the Acipenseridae (Huso huso, Acipenser gueldenstaedti, A. stellatus, Syngnathus nigrolinaetus, Alosa caspia nordmani, Zingel zingel, Z. streber) as well as some Gobiidae species (which according to some authors are present in unusual numbers in the Bulgarian Danube). Eudontomyzon donfordi is a rare species that was discovered in the Danube near the town of Oriahovo in 1992. As a result, the conservation status of the species was able to be changed from extinct to rare.

For ages the Danube ichthyofauna has been the object of both commercial and sport fishing. In recent decades, however, the populations of many species have changed dramatically. For example, the average annual fish catch between 1941 and 1958 was 930 tons; in the period 1960-74 it was 599 t; and in 1982 it was only 443 t. The catch has thus ceaselessly diminished with the years. The stock of the catches has also changed. For example, during the period 1925-58 Cyprinus carpio was the most numerous, constituting about 40.8% of the catch. In the years 1960-64 carp accounted for 30.4% of the catch, and remained first in rank. From 1965 to 1969 it continued to be the most numerous fish in the catch, but its proportion was only 12.3%. From 1970 to 1974 it accounted for 4.3% of the catch and fell to sixth in position. Now this species is threatened with extinction. Barbus barbus provides a contrasting example. In the period 1925-58 it accounted for 4.6% of the total catch, which placed it fourth in abundance. From 1960-1964 it comprised 3.5% of the catch. In the years 1965-69 it rose in the ranks to second place with 11%. From 1970-74, and continuing up to the present, it has been the most important species in the catch, reaching 21.6% in some fishing years.

There are many reasons behind the sharp decline in catches and the replacement of phytophilic species with reophilic species. First and foremost, the construction of hydroelectric projects along the Danube's upper and middle course and the blocking of its channel in Serbia by the "Jelezni vrata" ("Iron Gate") has altered the river's basic hydrological functions. Other critical factors are: the appropriation of river waters for industry and agriculture; the widespread pollution of the river waters; and, especially, the andigiring of the banks along the lower course of the river. The last of these prevents the phytophilic fishes from entering the lakes and floodplain waters. Although the andigiring of the Bulgarian riverbank has been complete for 30 years, this may have had only a slight impact on fish production, since there are few wetlands along the Bulgarian bank and they are small in size. By contrast, andigiring of the Rumanian riverbank, where the most important riparian and floodplain wetlands are located has significantly affected phytophilic and standing-water fish species that require vegetative substrates in their spawning cycle. Marinov (1978) pointed out that Barbus barbus, Abramis brama, and other species utilize the unused food resources of the carp, and because of this their biomass and numbers have significantly increased.

Statistical data indicate a drastic decrease in the catch (in tons) of the anadromous fish (Acipenceridae), as can be seen in the following table (Kolarov, 1989):

Species 1931-40 1961-70 1971-80 1981-86
Huso huso 482.9 262 149 45.3
A. gueldenstaedti 162.8 21.5 33.4 22.5
A. stellatus 96.6 9.4 4.4 4.5

These numbers represent the average amounts of fish caught in the freshwaters and seas of Bulgaria, the former Soviet Union, and the former Yugoslavia. The numbers have continued to decrease since 1987. There are several main reasons for the sharp decreases in stocks of these fish: the continued unreasonable commercial fishing of these species, especially prior to the reproduction period; a total lack of limitations on the catch, even as parent stocks have been reduced many times over (some of the controls on catch sizes instituted by the International Committee on Fish Catches are ineffective); the biologically groundless monthly ban on catching anadromous species of the family Acipenseridae, as it does not provide protection when they enter the river; hydroelectric constructions along the Danube, especially the building of dams Jerdap-1 (at km 943) and Jerdap-2 (864 km), which will lead to total liquidation of the species from the Acipenseridae family; increasing pollution of the Danube's water; and numerous other negative anthropogenic influences.

The Acipenseridae family is of special concern. The critical state of the stocks of Acipenseridae species cannot be improved rapidly. Due to their long life cycles and the late onset of maturity in these species,at least 8-10 years are required to establish trends in their populations. Strong external measures, not previously applied, are needed to protect the stocks. The introduction of temporary (10-year) fishing moratoria for Huso huso and A. gueldenstaedti, and the listing of A. stellatus in the red data books of the countries in the Black Sea-Danube River system are the only rational measures that can succeed in saving their populations from slow but certain destruction. Mass artificial reproduction of species from this family has to be the other step, organized internationally by the countries that exploit them.

The Tributaries of the Bulgarian Danube

There are 13 tributaries of the Danube River in Bulgaria. There length varies from 60 km (the Archar River) to 368 km (the Iskar River). Their catchment area amounts to 33.371 km2 - about 30% of the Bulgarian land surface. Their upper courses go through mountainous areas, while their middle and lower courses go through the Danubian plain. They are this characterized by a wide variety of ecological conditions. This factor, combined with the rivers' direct connection to the Danube, accounts for their varied ichthyofauna.

The first data about the ichthyofauna composition of the Bulgarian Danube tributaries come from the work of Kovatchev (1909, 1910, 1923). Shishkov's investigations (1929, 1937a, 1937b, 1939a, 1939b, 1940, 1942, etc.) were mainly taxonomic, but also considered the diversity and distribution of the fish species. Drensky's scientific articles (1921, 1922, 1926, 1928, 1932, 1943, 1948) as well as his monograph (1951) are definitive contributions for the protection of the Bulgarian ichthyofauna.

In the last few decades, intensive and important ichthyological studies have been conducted. They include investigations of all the Danube tributaries (Paspalev and Dikov, 1989; Georgiev, 1967; Michailova, 1970; Sivkov, 1980, 1985, 1986, 1988, 1989, 1991; Karapetkova, 1972, 1976, 1979, 1985a, 1985b, 1989; Karapetkova and Dikov, 1986; Karapetkova and Pomakov, 1982, 1982; Karapetkova and Undjian, 1988; etc.). The quantity, productivity, and biological characteristics of the different species have been studies by Dikov and Zivkov (1985), Dikov et al. (1988), Iankov and Dikov (1985), Iankov (1987), Iankov and Zivkov (1988), etc. Although the ichthyofauna of the Bulgarian Danube tributaries continues to be an object of research, many of the results that have been obtained in recent years have not yet been published in the scientific literature. In this regard, the contemporary data about the ichthyofauna conditions have not been available.

The ichthyofauna of the Bulgarian Danube tributaries is presented in Appendix 1. It consists of 59 taxa belonging to 15 fish families. Cyprinidae, with 28 species, is the most represented, followed by Percidae (8 species), Gobiidae and Cobitidae (5 species each), and so on. According to their distribution in the different rivers, the fish can be divided into the following groups:

Species distribution along the rivers follows a characteristic pattern. The upper courses are inhabited by Salmo trutta fario, joined soon thereafter by Salmo gairdneri. These species do not reproduce naturally in the rivers, and occur there due to artificial stocking. As Salmo trutta fario diminishes in number downstream, Phoxinus phoxinus, Alburnoides bipunctatus, Cottus gobio, and Barbus meridionalis petenyi appear. The lower extent of distribution of Phoxinus phoxinus, Alburnoides bipunctatus, and Cottus gobio coincides with the end of the mountain zone. However, Barbus meridionalis petenyi remains widespread along the middle course also, and even occurs in some parts of the lower course. Some Cyprinidae, such as Leuciscus cephalus, Chondrostoma nasus, Barbus barbus, Alburnus alburnus, Rhodeus sericeus amarus, some species of Gobiidae, some species of Cobitidae, etc., are represented by relatively abundant and stable populations, especially in the middle courses of the rivers. Confined primarily to the lower river courses are Scardinius erythrophthalmus, Abramis brama, A. ballerus, A. sapa, Blicca bjorna, Rutilus rutilus, Carassius auratus gibelio, Cyprinus carpio, Silurus glanis, Esox lucius, the species from Gymnocephalus, Perca fluviatilis, etc. At this point the typical Danube fishes - Aspius aspius, Leuciscus idue, Lota lota, Acipenser ruthenus, etc. - are again encountered.

Appendix 3 includes information on the ranges of the rare fish in Bulgaria. Many species of the Bulgarian Danube tributaries fall under this category. In addition to those listed in the Bulgarian Red Data Book, species representing the genera Coregonus, Thymalus, Ictiobus, Ictalurus, and others should be considered rare. Salmo trutta labrax, Hucho hucho, Gobio uranoscopus, Sabanejwia bulgarica, Zingel zingel, and Zingel streber are also rare.

Endemic species (Appendix 4) include Cottus gobio haemusi at the subspecies level, as well as the Danube endemics that enter the lower courses and mouths of the tributaries: Gymnocephalus schraetzer, G. baloni, etc.

General Assessment and Recommendations

The ichthyofauna complex has been enriched in recent decades, despite the degradation of ecological conditions during the same period. Since the ichthyofauna has begun to be more systematically studied, some species new for the territory of Bulgaria have been discovered. At the same time, other species have expanded their ranges either naturally or through artificial fish breeding. In this fashion, for example, Lepomis gibbosus and Pseudorasbora parva have come to be found everywhere in Bulgarian over the last few decades.

Other distinctive (and destructive) changes in the river ichthyofauna during the past several decades have been the shift in dominant species and the decline in the general biomass of fish populations. The problems involved in preserving and expanding the river fish stocks are very well known. Effective solutions will require that the following measures be taken:

The Black Sea Watershed

The Bulgarian Black Sea Rivers

Nineteen rivers (in addition to the Rezovska River on the Bulgaria-Turkey border) belong to the Black Sea watershed area in Bulgaria. Twelve of them flow directly into the sea, and 8 flow into the seaside lakes - Beloslavsko (Gebedzhensko), Bourgasko, and Mandrensko. These Black Sea tributaries vary in size. The Perpedere River is only 14.5 km long, while the Kamchia River stretches 245 km long. The areas of their watersheds vary from 50.5 km2 (the Sarandere River) to 5357 km2 (the Kamchia River). They are characterized by the relatively low altitude of their watersheds, the small declivity of their river beds, and a well developed network of braiding in their lower courses. The areas near the mouths of the rivers are strongly affected by the sea or by the lakes respectively.

Strong east winds cause alluvial sands to gather in front of some of the rivers flowing into the sea, blocking the outflows of the rivers. Only the Veleka River remains open throughout the year. The mouth of the Ropotamo River has been dredged and allows salty water to reach about 7-8 km up the course of the river. In the last few years, however, the Ropotamo River was once again almost closed due to the destruction of the protective dike and a decreasing flow of river water. At present, the Ropotamo reaches the sea through a shallow channel.

Relatively complete studies of the ichthyofauna of the Black Sea rivers were carried out in the period 1965-1976 (Peshev, 1965, 1969, 1970; Apostolov, 1972; Karapetkova and Peshev, 1973; Karapetkova 1974, 1975, 1976). Only the ichthyofauna of the Rezovska River was not investigated. In recent years the conditions of the Black Sea rivers have changed. Several dams have been built, including the Yasna Polyana, the Kamchia (Ticha), and the G. Trajkov. Some parts of the rivercourses were redirected. These changes have certainly resulted in considerable changes to the rivers' ichthyofauna, but there are not up-to-date data on species composition or, especially, the size of the fish populations.

The ichthyofauna of the Bulgarian Black Sea rivers includes a total of 77 species and subspecies, which fall into two groups: permanent residents of the rivers (39 species) and species residing temporarily in the rivers after entering from the Black Sea and nearby lakes (38 species). (See Appendix 2).

The group of permanent residents consists mainly of primarily freshwater species (31 of 39 species). Some sea species can be found in the rivers: 6 are indigenous Ponto-Caspian relicts, one is a Boreal-Atlantic relict, and one is a Mediterranean immigrant. The Cyprinidae family is the most widely represented, with 21 species, followed by Gobiidae with 5 species (all of which are completely adapted to fresh water). The significance of the Gobiidae is further illustrated by the presence of another five species that temporarily enter the rivers. A number of species - including Leuciscus cephalus, Chalcalburnus chalcoides, Gobio gobio, Alburnus alburnus, Alburnoides bipunctatus, Barbus meridionalis petenyi, Barbus tauricus, Vimba vimba tenella, and Rhodeus sericeus amarus - are represented by abundant stable populations, especially in the larger rivers. They are especially important in that they are spread over long stretches of the rivers. By contrast, other species that are just as abundant are restricted to short sections of the rivers: Rutilus rutilus, Rutilus frisii, Leuciscus borysthenicus, Scardinius erythrophthalmus, Cyprinus carpio, Carassius auratus gibelio, Neogobius melanostomus, etc.

The temporary residents consist exclusively of species that originated primarily in the sea. Mediterranean immigrants (29 species) form the most numerous group in this category, followed by the indigenous Ponto-Caspian species (5) and Boreal relicts (4). This complex was enlarged by the presence of a considerable number of typical sea species in the firth zone of the Ropotamo River prior to its recent closing. Their presence there, as well as in some other rivers, is accidental. By contrast, the species from the families Clupeidae, Mugilidae, and Gobiidae, as well as Anguilla anguilla, Atherina mochon pontica, and other species must migrate into the river waters to feed and reproduce. The temporary residents live both in brackish waters as well as the fresh waters of the firth zone. Some species migrate long distances from the river mouth (e.g., Alosa caspia bulgarica, Anguilla anguilla, etc.). Species occurring in the most rivers include Mugil cephalus, Liza saliens, Atherina mochon pontica, Platichthys flesus luscus.

Endemic taxa found in the Bulgarian Black Sea tributaries are Alosa caspia bulgarica (distributed in the southern Black Sea tributaries and along the southern Black sea coast) and Cobitis peshevi spp. nov. (found in the Black Sea and Aegean Sea tributaries).

The density of fish populations in the small rivers fluctuates widely. Because of rapid changes in the abiotic environment, the simplified food chains in the rivers, and the high reproductive capacities of the species, some populations can multiply quickly in a very short time, while at other times there will be no fish at all.

In general, the fish stocks of the rivers along the Bulgarian Black Sea coast are not rich. They have not been subject to commercial fishing, neither in the past or in recent decades. However, they have been used as a food supply for local people in the past, and are increasingly used for sport fishing nowadays.

The most important factors influencing the ichthyofauna in the Bulgarian Black Sea rivers are:

There are 19 small and larger lakes and swamps along the Bulgarian Black Sea coast. However, only 7 or 8 of them deserve special attention for their ichthyological and economic importance.

The largest seaside lakes have been well studied, both in the past (Drensky, 1922; Netchaev, 1932-1944; Valkanov, 1935-1941; Paspalev, 1944; and others) and in recent decades (Alexandrova, 1957-1980; Ivanov, 1967-1980; Zashev and Angelov, 1959; Kolarov, 1962, 1967). All the species of fish in these lakes have been studied and described by Georgiev (1967), and supplemented by other authors. This high level of interest is attributable to the peculiar genetic characteristics and high fish production of the lakes, as noted a number of years ago.

In the last decade, the observations undertaken on these lakes have been very scarce. There is no recent data about their condition. In the years 1990-1992, research has been conducted only on Varnensko and Beloslavsko Lakes.

The ichthyofauna of the seaside lakes includes a total of 79 species and subspecies, 43 of which are permanent residents of the lakes and 36 of which enter the lakes occasionally or regularly for feeding, reproduction, and hibernation (Appendix 2).

Changes in the composition and number of fish in the seaside lakes depends on different factors that are quite specific to each of them. For this reason the lakes are described here separately.

Blatnishko (Durankulashko) Lake

This lake is separated from the sea by an alluvial sand bar. However, in years of plentiful rainfall, a natural temporary connection to the sea is created or a canal is dug through. This allows species from the families Mugilidae, Atherinidae, and Pleuronectidae to enter the lake and temporarily enrich the lake ichthyofauna.

There are 16 year-round inhabitants of Blatnishko Lake, of which 9 are freshwater fish species and 6 are indigenous sea species; the Mediterranean immigrants are represented by one species. The Ponto-Caspian relicts Clupeonella cultriventris, Pungitius Platygaster, and Knipowitschia caucasica, as well as the freshwater fishes Chalcalburnus chalcoides and Vimba vimba tenella, are small in number and threatened by extinction.

There is not pollution in the lake. However, its water is used for irrigation, which has negative effects on the reproduction of the different populations, mainly by decreasing the extent of their breeding areas.

Shablensko and Ezeretsko Lakes

Both lakes are closed firths connected by a shallow canal. They are separated from the sea by a narrow sand bar. In some years the ichthyofauna is enriched by eurichalinen species from the sea. The fish fauna of these lakes includes 15 permanent resident species, 7 of which are freshwater fishes, 7 autochthonous, and one a Mediterranean immigrant.

In these lakes are 4 Ponto-Caspian relict species, including Clupeonella cultriventris, which is extinct along the Bulgarian sea coast, as well as Pungitius platygaster and Benthophiloides brauneri, which have constantly diminished in number. The latter species is found in Bulgaria only in Shablensko Lake.

The fish fauna of the two lakes is of special interest from a zoogeographic standpoint. Some species found here - including Danubian elements such as Esox lucius, Abramis brama, and Misgurnus fossilis - are not found in lakes situated further south.

The protected status of these lakes should be discussed and legalized.

Beloslavsko (Gebedzhensko) Lake

Up until 1923 Beloslavsko Lake was a closed body of freshwater connected to Varnensko Lake by a shallow river. In 1976 the lake was turned into a navigable canal (the "Varna Bay-Beloslavsko Lake") and its salinity increased to the level of that in Varna Bay.

Georgiev (1967) found and noted 21 permanent resident fish species and 10 recurrent or occasional resident species. Most numerous are the freshwater fish species (12), the autochthonous sea species (7), and the Mediterranean immigrant species (2).

Up until 1976, Beloslavsko Lake was one of the most productive of the seaside lakes. Cyprinus carpio, Atherina mochon pontica, Clupeonella cultiventris, and Mugil cephalus were among the species of essential economic importance. After the lake was turned into a navigable canal, the incidence of pollution also rose sharply. In addition, part of its area was reduced. In this way Knipowitschia longicaudata disappeared from the Bulgaria ichthyofauna. Some rare and threatened species - Clupeonella cultiventris, Leucaspius delineatus, Gasterosteus aculeatus, Pungitius platygaster, Atherina mochon pontica, Knipowitschia caucasica, etc. - were annihilated.

Varnensko Lake

This is an open firth connected to the sea and to Beloslavsko Lake. In 1909 the first sea-lake canal was built, followed in 1923 by a second canal linking Beloslavsko and Varnensko Lakes. In 1976 a navigable canal was built between Varna Bay and Beloslavsko Lake. Since then the salt regime of Varnensko Lake has been the same as that of the adjoining bay.

Georgiev (1967) described 26 permanent resident species and 29 periodic or occasional species that enter the lake. By origin they are distributed as follows: 9 freshwater species, 11 autochthonous Caspian relict species, 4 Boreal relicts, and 31 Mediterranean immigrants. Alexandrova and Kolarov (unpub. data) inventoried 38 species in Varnensko Lake in 1990-92. Sixteen qualified as permanent residents and 22 as occasional or periodic visitors entering the lake for feeding, reproduction, and hibernation. The latter are mostly sea fish.

The increased salinity of the lake water has had changes of essential importance in the condition of the ichthyofauna and the size offish populations, and has exacerbated the effects of pollution from industrial and urban drainage waters. An additional factor affecting fish populations is thermal pollution form the Thermo-electric Power Station. The regular dredging of the navigation channel has also had a negative effect on the breeding grounds of the Gobiidae, Blenniidae, and other families.

Annually, millions of fish - mostly Mugil cephalus and Liza saliens - are killed. A great deal of fish mortality is due to the effects of eutrophication during the summer months. Freshwater fish, as well as Gobius ophiocephalus, Clupeonella cultiventris, and others, have disappeared. In order to reduce pollution and protect both the genetic and economic resources of the fish in the lake, a combination of measures are needed.

Pomoriisko Lake

This is a lagoon connected to the sea by a narrow and shallow channel. The ichthyofauna of the lake is very poor because of its high level of salinity and the insufficient link to the sea. The only permanent resident of the lake is Knipowitschia caucasica. In some years the lake has been naturally or artificially stocked with sea fish species such as Mugil cephalus, Liza auratus, Liza saliens, Atherina mochon pontica, and Platichthys flesus luscus.

Bourgasko Lake

This is a shallow firth connected to the sea through a canal. In the last two decades the inflow of sea water has been reduced and the lake has become a freshwater basin.

The permanent residents of the lake, as studied by Georgiev (1967), total 19 species: 9 freshwater fish species, 7 autochthonous sea species, and 3 Mediterranean immigrants. Temporary visitors and occasional or regular immigrants to the lake amount to 10 species, including the Mediterranean immigrants Mugil cephalus, Liza auratus, Liza saliens, and Atherina mochon pontica.

Artificial breeding of Cyprinus carpio, Hypophthalmichys molitrix, Ctenopharingodon idella allowed these species to become first-rate economic resources. In the past Bourgasko Lake was known as a rich feeding area for fish and had high rates of fish production. But after the building of the Oil-Chemical plants near the town of Bourgas, the lake was systematically polluted and the fish became inedible.

The existing fish in the lake are poisoned periodically. The species that in the past were identified as the most rare and vulnerable have now become extinct within the lake. Other species are now experiencing the same trend.

Mandrensko Lake

Up until 1962 this lake was connected to the sea through a deep canal. In 1962 a dam-wall was built and a great part of its area turned into a reservoir. The eastern part of the lake, called Usungeren, maintains its link with the sea and so has a salinity level similar to that of the sea. The ichthyofauna of the reservoir part comprises 18 species - 8 freshwater fish species, 8 autochthonous species, and 2 Mediterranean immigrants. By opening the lock of the dam, many sea species (e.g., Mugilidae, etc.) enter the lake.

Usungeren has 11 permanent resident species. Of this group, 6 are autochthonous sea species, 4 are Mediterranean immigrants, and one species is of freshwater origin. Temporary residents in that part of the lake number 15 species altogether, chiefly representatives of Mugilidae, as well as occasional coastal and freshwater species.

Irrigation has had a negative effect on the ichthyofauna, destroying their natural breeding grounds.

The seaside lakes are distinguished by the unique composition of their ichthyofauna, their productivity, and the low net price of their fish production in the past. Now, according to available data, fish production is being negatively affected, especially in some lakes. The worst conditions are in Beloslav Lake, which is essentially a dead water basin. The conditions in Varnensko Lake are almost the same in certain aspects. More than tragic is the condition of Bourgasko Lake, where the fish fauna, though not destroyed, is unsuitable for consumption due to the accumulation of petroleum products within the fish. The other seaside lakes are in relatively better condition.

The essential problems involved in protecting the genetic resources of the lakes and in rationally utilizing the fish stocks where they exist can be addressed by:

The Aegean Sea Watershed

The watershed of the Aegean Sea in Bulgaria consists of several river valleys that gather water from the whole souther part of the country. The valley of the Maritsa River is the largest, with a catchment are of 21,840 km2. Its tributaries, the Tundzha and Arda Rivers, which join the Maritsa outside of Bulgaria, have a total catchment area of 10,791 km2, while that of the Mesta River is 2,764 km2. These figures take into account the watershed of the rivers up to the Bulgarian frontier with Greece and Turkey. Thus, the lower courses of the southern Bulgarian rivers, the ichthyo-fauna of which are relatively richer, are not included.

Research on the ichthyofauna in these streams has developed along two lines. The morphological characteristics and taxonomic status of the different species have been studies by Chichkov (1937, 1939, 1940a, 1940b, 1943, etc.), Drensky (1923, 1926, 1928, 1934, 1943, etc.), Marinov (1964, 1973a, 1973b, 1975), Michailova (1970), Pechev (1971), and others. Along with these studies some researchers have undertaken surveys of the Aegean watershed in general (Chichkov, 1939) or of the various rivers, such as the Strouma (Kovatchev, 1921; Bulgurkov, 1958; Michailova, 1965) and Maritsa (Kovatchev, 1921; Dimov, 1939; Michailova, 1965). Data on the composition and distribution of the fishes in the southern Bulgarian rivers can be found in the monographic works of Kovatchev (1923), Morov (1931), and Drensky (1951).

Despite these many scientific works, the ichthyofauna of the rivers in the Aegean watershed remains the most poorly investigated. There are, for example, no published data on the fish fauna of the rivers Topolnitsa, Tundzha, Arda, and Mesta, and this can be said as well for many of the tributary streams. Moreover, all the available data on the fishes of the basin can be considered obsolete and in need of revision.

The ichthyofauna of southern Bulgaria includes a total of 50 species and subspecies (Appendix 1). The most numerous are those of the Cyprinidae (24 species), followed by Cobitidae (6), Salmonidae (3), and the other families (represented by just one species each). Species with relatively abundant and widely spread populations include Leuciscus cephalus, Barbus cyclolepis cyclolepis, Alburnus alburnus, Chondrostoma nasus vardarenses, Scardinius erythrophthalmus, Gobio gobio, Phoxinus phoxinus, Rhodeus sericeus amarus, and Carassius auratus gibelio. In addition to these species, Cobitis taenia, Sabanejwia aurata balcanica, Silurus glanis, Esox lucius, Perca fluviatilis, Proterorhinus marmoratus, and others are also numerous. Gambusia affinis holdrooki is characterized by high numbers in many smaller water basins, while Lepomis gibbosus and Pseudorasbora parva have recently multiplied. By contrast, species such as Gasterosteus aculeatus, Cottus gobio, and Stizostedion lucioperca are restricted in number and distribution. Members of the Catostomatidae and Ictaluridae, as well as Coreconus lavaletus, which are now becoming acclimated to this area, can be included in the same category. The arrival of Anguilla anguilla and Acipenser sturio in the Bulgarian rivers has not been confirmed by recent data.

The Aegean watershed within the Bulgarian borders is noted for its large number of endemic forms (Appendix 4). The following species and subspecies are characteristic for the Balkan Peninsula: Vimba melanops, Cobitis peshevi, Rutilus rutilus mariza, Barbus cyclolepis cyclolepis, Chondrostoma nasus vardarenses, Sabanejwia aurata balcanica, and Noemachilus angorae bureshi.

A new species, Cobitis peshevi, has recently been described for the Black Sea and Aegean basin (Sivkov and Dobrovolov, 1986). At this point it has not been specified whether it is an endemic form for Bulgaria or for the Balkan Peninsula.

The problems concerning the protection of the ichthyofauna and rational utilization of the fish resources in the Aegean basin rivers of Bulgaria are the same as those faced by the rivers in the Danube River and Black Sea watersheds.

It is recommended that Vimba melanops and Barbus cyclolepis, for which the Maritsa River is terra tipica, be immediately placed under legal protection on the lower course of the Vatcha River and on the Shirokolashka Rivers, where these two species can also be found.

Standing Waters

Bulgaria's standing waters are divided here into two categories: mountain lakes and artificial water basins.

Mountain Lakes

There are three types of lakes in the Bulgarian mountains: glacial, landslide, and tectonic. The glacial lakes number about 260 (140 in the Rila Mountains and 120 in the Pirin Mountains). About 50 smaller lakes, 0.1-0,2 ha in size, are not included in this figure, because they are often dry in the summer. They are located at altitudes of 1858 to 2709 m above sea level. Their depth varies from 0.5 to 29.5 m. Almost all are characterized by extreme changes in water levels and low biological productivity. However, the lower lakes are stocked with Salmo trutta fario, which is a subject of sport fishing. No research on their stocks is being carried out. Leuciscus souffia is found in the Dolno Kremensko Lake in the Pirin Mountain (Karapetkova, Marinov, 1991).

There are three landslide lakes: Smolianski and Chairski Lakes in the western Rhodopes, and Kostensko Lake in the Rila Mountains. They have the highest pH levels (pH=6-6.9) ever established in our country. Due to this peculiarity, they are low in biological productivity. Recently some of them were artificially stocked with Ctenopharingodon idella, which cleaned out almost entirely the floating aquatic flora. Attempts to introduce Salmo gairdneri irideus, Salvelinus fontinalis and Coregonus lavaretus have been carried out, but so far without success. The species Cyprinus carpio and Scardinius erythrophthalmus are among the others that are also found in these lakes (Appendix 1) (Karapetkova, 1987; Karapetkova and Zivkov, 1989).

There are 10 tectonic lakes and wetland basins in the Rila, Pirin, and Stara Planina Mountains with a total area of 1,500 ha. The largest are Skala, Panitckishte, and Kupensko Lakes, and the three wetlands of the Klutch area in the Stara Planina Mountains. They are rich in plankton and benthos and are stocked mainly with carp. Ichthyological investigations have not yet been carried out there.

Artificial Water Basins

The artificial water basins in Bulgaria include reservoirs (mountain, lowland, and small dam) and fish farm facilities.

a. Reservoirs

In Bulgaria, reservoirs created by dams cover a total area of 39,500 ha. Larger reservoirs, over 200 ha in size, predominate (61.6% of the total). They contain a high volume of water, but the water level over the course of the year fluctuates widely. These characteristics are not favorable for the development of a specific aquatic flora within them, which is an absolutely necessary condition for the natural reproduction of phytophilic fish species. This results in a relatively poor level of species diversity and low fish reserves in most of them. In terms of their ecology and fish productivity, the reservoirs in the mountain and plain regions differ considerably.

Mountain reservoirs

These reservoirs are classified as high mountain (over 1800 m above sea level) and middle mountain (600-1800 m above sea level) according to their altitude.

The high mountain reservoirs are relatively few in number: the Beli Iskar, the Goliamoto Smradlivo, the Gornoto ribno, the Karagiolskoto, and several others. They are characterized by poor trophic bases, low summer temperatures (4-15 °C), and low levels of biological productivity. Ichthyological investigations have not yet been carried out. Only Salmo trutta fario can be caught in these lakes.

The most numerous and well studied from an ichthyological standpoint are the middle mountain reservoirs. This category includes the reservoirs of all our basins: Batashka, Dospadska, Iskarska, and others (Zivkov, 1974, 1975, 1976, 1980, 1987; Zivkov and Stoyanova, 1976; Zivkov and Grupcheva, 1979; Zivkov and Petrova, 1983, 1984; Naumova and Zivkov, 1988; Dikov and Zivkov, 1985). Most are relatively large and long, with a total area of 7,500 ha. They are characterized by their rich lower flora and fauna, consisting primarily of planktonic species. Their potential fish production is estimated at about 0.5-1.2 kg/ha, but the actual figure is less than 0.1-0.5 kg/ha. Industrial fishing is conducted only in the Batak and the Dospat reservoirs. Many of the middle mountain reservoirs are used as a medium for the artificial breeding of Salmo gairdneri irideus and Cyprinus carpio in confinement. Some 1,000 to 3,000 tons of rainbow trout are produced annually in this way in the Dospat reservoir.

The diversity of species in the middle mountain reservoirs is illustrated by the ichthyofauna of the Batak dam: Cyprinus carpio, Carassius carassius, Carassius auratus gibelio, Tinca tinca, Leuciscus cephalus, Rutilus rutilus, Alburnus alburnus, Gobio gobio, Scardinius erythrophthalmus, Barbus cyclolepis, Rhodeus sericeus amarus, Vimba melanops, Ctenopharingodon idella, Salmo gairdneri irideus, Hypophthalmichthys molitrix, Coregonus albula, Stizostedion lucioperca, Perca fluviatilis, Lepomis givvosus, and Silurus glanis. The same species are found in the Dospat reservoir except for Rhodeus sericeus amarus, Ctenopharingodon idella, Stizostedion lucioperca, Hypophthalmichthys molitrix, and Silurus glanis. However, others are found there: Coregonus peled, Chondrostoma nasus, and Noemacheilus barbatulus.

Dams in the plain regions

Reservoirs situated below 600 m above sea level are called "plain region" or "lowland" reservoirs. These are the most numerous and include some of the largest in Bulgaria (Mandra, Al. Stamboliiski, G. Dimitrov, Studen Kladenez, Jrebtchevo, Ovcaritsa, Ivailovgrad, and others).

Especially well studied from an ichthyological standpoint are Al. Stamboliiski, G. Dimitrov, Ovcaritsa, and Piasatchnic (Marinov and Boiadjiev, 1967; Boiadjiev, 1969; Dimitrov and Lyudskanova, 1967; Zivkov and Grouptcheva, 1989; Pavlov et al., 1989). They are characterized by an active exchange of water, thick sediment layers with rich benthos, and high maximum summer temperatures (27-29 °C). In the cooling ponds of the thermoelectric power stations, temperatures can rise to 37°C (at the dams Ovcaritsa and Rosov kladenez), with frequent oxygen saturation in the upper layers and low quantities of oxygen in the lower layers. Thus, despite the high potential of these lakes for fish reproduction, actual catches do not exceed 24-59 kg/ha (the deep water plankton and benthos are not available to the economically valuable fish species).

Species diversity in these reservoirs is well illustrated by the ichthyofauna of the Ovcaritsa, where the highest number of species (22) has been established: Rutilus rutilus, Leuciscus cephalus, Tinca tinca, Scardinius erythrophthalmus, Aspius aspius, Alburnus alburnus, Abramis brama, Vimba melanops, Cyprinus carpio, Carassius carassius, Carassius auratus gibelio, Ctenopharyngodon idella, Aristichthys nobilis, Hypophthalmichthys molitrix, Gambusia affinis, Cobitis taenia, Silurus glanis, Stizostedion lucioperca, Perca fluviatilis, Gymnocephalus cernua, Lepomis gibbosus, and Proterorhinus marmoratus.

Thirteen fish species are found in the Al. Stamboliiski reservoir and 15 in the G. Dimitrov. Almost all the plains reservoirs are stocked with carp, pike, perch, and herbivorous species. Recently, other species such as Ictalurus punctatus, Ictiobus cyprinelus, Ictiobus bubalus, Ictiobus niger have been introduced to some of these water bodies.

Microdams

About 3,000 small dams have been built for irrigation and fish breeding on Bulgaria's small rivers and streams. They are filled with water in winter and spring, mainly from rainfall. Some are drained in the autumn. Their watersheds include cultivated and fertilized areas, assuring them an ample supply of phosphorous and nitrogen and thus making them suitable for fish production. They are stocked mainly with carp and herbivorous fish. Their natural fish productivity can reach 200-500 kg/ha. Their fish fauna coincides with that of the small rivers that feed them, but often goldfish, american sunfish, roach, perch, and other species are introduced along with the stocking material. Ichthyological studies have not been carried out in them.

b. Fish Farms

Bulgaria has about 3,300 ha of fish production basins. The processes of fish reproduction, feeding, growth, etc. in the fish farms is completely controlled. They have two main functions: production of stocking material and production of fish for consumption. Carp, herbivorous species, silver carp, grass carp, rainbow trout, brown trout, buffalo fish, and channel catfish are among the preferred species for artificial reproduction and distribution.

Status of Fish Stocks in the Standing Waters

The fish stocks in Bulgaria's standing waters are decreasing. In most of the large Bulgarian reservoirs, they are depleted to such an extent that commercial-scale fishing has been stopped. The main reasons for the decreases are:

1. The great depths and fluctuations in the water level in the reservoirs hinders the development of water flora in the shore area, which makes natural reproduction of phytophilic fish impossible. The number of non-valuable species rapidly increases, leading to decreases in the reproduction of economically important species.

2. Artificial breeding in these reservoirs is unsatisfactory, sporadic, and often undertaken with unsuitable species; in short, it is poorly grounded scientifically. The development of the fish fauna is unguided. It usually consists of species that cannot efficiently utilize the nutritional base in these reservoirs.

3. Fish farming in these areas is not successfully organized. The fish resources of a single dam are often overseen by several administrative bodies, but none of them take real responsibility for their rational use, protection and reproduction.

4. The level of the allowable catch in the Bulgarian reservoirs is determined arbitrarily. It is often biologically inappropriate. This results in the destruction of the biological balance, which cannot then be restored for many years.

5. In some reservoirs (e.g., the Dospot), the number of cages and the quantity of artificially reared rainbow trout in them are also scientifically ungrounded. This sometimes leads to the overloading of the water basins with organic substances. The consequences are fish poisoning, algae "blooms," and other symptoms of eutrophication.

6. Co-ordination between fish farming and reservoir water consumption is lacking. During the reproductive period of the economically valuable fish species, measures to control water levels are not carried out, which hinders natural fish reproduction.

To solve these problems, and to assure the rational use, protection, and restoration of fish resources, special and important measures will be required.

Appendix. 1 Species Composition of Bulgaria's Freshwater Fish (Danube River and Aegean Basin)

Species Danube River Danube Tributaries Aegean Basin Mountain Lakes Mountain Dams Plain Dams Micro dams Fisheries
1 2 3 4 5 6 7 8 9
Cyclosonmata: Petromyzonidae                
1. Eudontomyzon danfordi (Regan, 1911) +              
Pices Osteichthyes Acipenseridae                
2. Huso huso (Linnaeus, 1758) +              
3. Acipenser nudiventris Lovetzky, 1828 +              
4. Acipenser ruthenus Linneaus, 1758 + +            
5. Acipenser sturio Linneaus, 1758 +   +          
6. Acipenser stellatus Pallas, 1771 +              
7. Acipenser gueldenstaedti Brandt, 1833 +              
Clupeidae                
8. Alosa pontica pontica (Eichwald, 1838) + +            
9. Alosa caspia nordmani (Antipa, 1906) +              
Salmonidae                
10. Salmo trutta fario Linnaeus, 1758   + + + +     +
11. Salmo trutta labrax Pallas, 1811 +              
12. Salmo gairdneri irideus Gibbons, 1855   + + + +     +
13. Salvelinus fontinalis (Mitchill, 1815)     + + +      
14. Hucho hucho (Linnaeus, 1758) +              
Coregonidae                
15. Coregonus lavaretus (Linnaeus, 1758)   + + + +      
16. Coregonus peled (Gmelin, 1738)   +     +      
17. Coregonus albula (Linnaeus, 1758)         +      
Thymallidae                
18. Thymallus thymallus (Linnaeus, 1758)         +      
Escocidae                
19. Esox lucius Linnaeus, 1758 + + +     + +  
Cyprinidae                
20. Rutilus rutilus mariza Drensky, 1926 + + +   + + +  
21. Leuciscus cephalus (Linnaeus, 1758) + + + + + + + +
22. Leuciscus souffia Risso, 1826       +        
23. Leuciscus borysthenicus (Kessier, 1859)     +          
24. Leuciscus idue (Linnaeus, 1758) + +            
25. Phoxinus phoxinus (Linnaeus, 1758)   + +   +      
26. Sardinius erythrophthalmus (Linnaeus, 1758) + + +   + + + +
27. Aspius aspius (Linnaeus, 1758) + + +     +    
28. Tinca tinca (Linnaeus, 1758) + + + + + + + +
29. Chalcalburnus chalcoides (Cueldenstaedt, 1772) + +            
30. Alburnus alburnus (Linnaeus, 1758) + + + + + + + +
31. Alburnoides bipunctatus (Bloch, 1782)   + +   + + +  
32. Blicca bjoerkna (Linnaeus, 1758) + +            
33. Abramis brama Linnaeus, 1758 + + +   + + +  
34. Abramis sapa (Pallas, 1811) + +            
35. Abramis ballerrus (Linnaeus, 1758) + +            
36. Vimba vimba carinata Pallas, 1811 + +            
37. Vimba melanops Heckel, 1840     +     + + +
38. Pelecus cultratus (Linnaeus, 1758) + +            
39. Chondrostoma nasus nasus (Linnaeus, 1758) + +     + + + +
40. Chondrostoma nasus vardarensis Karaman, 1928     +   + + + +
41. Rhodeus sericeus amarus Bloch, 1782 + + +   + + + +
42. Pseudorabora parva (Schlegel, 1842) + + + + + + + +
43. Gobio gobio gobio Linnaeus, 1758 + + + + + + + +
44. Gobio uranoscopus (Agassiz, 1826)   +            
45. Gobio kessleri Bybovsky, 1862 + +            
46. Gobio albipinnatus Lukasch, 1933 + +            
47. Barbus barbus (Linnaeus, 1758) + +       + + +
48. Barbus tauricus bergi (Chichkov, 1935)     +     +    
49. Barbus meridionalis petenyi Heckel, 1847   +   +        
50. Barbus cyclolepis Heckel, 1840     +   + + + +
51. Cyprinus carpio Linnaeus, 1758 + + + + + + + +
52. Carassius carassius (Linnaeus, 1758) + + + + + + +  
53. Carassius auratus gibelio (Bloch, 1782) + + + + + + + +
54. Hypophthalmichthys molitrix Valenciennes, 1844 +   +   + + + +
55. Aristichthys nobilis Richardson, 1845 +   +   + + + +
56. Ctenopharingodon idella Valenciennes, 1844 +   + + + + + +
Catostomidae                
57. Ictiobus cyprinellus Valenciennes, 1844     +   + + + +
58. Ictiobus bubalis Radinesque, 1810     +   + + + +
59. Ictiobus niger Rafinesque, 1810     +   + + + +
Cobitidae                
60. Noemacheilus barbatulus Linnaeus, 1758 + + +   +      
61. Noemacheilus angorae bureschi Drensky, 1928     +          
62. Misgurnus fossilis Linnaeus, 1758 + + +       + +
63. Cobitis taenia Linnaeus, 1758 + + + + + + + +
64. Cobitis elongata elongata Heckel and Kner, 1858 + +            
65. Cobitis peshevi Sivkov and Dobrovolov, 1986   + +          
66. Sabanejwia aurata balcanica Karamann, 1922   + +   +      
67. Sabanejwia bulgarica (Drensky, 1928) + +            
Siluridae                
68. Silurus glanis Linnaeus, 1758 + + +   + + + +
Ictaluridae                
69. Ictalurus nebulosus (Le Sneeur, 1819)     +   + + + +
70. Ictalurus punctatus (Rifanesque, 1810)     +   + + + +
Anguillidae                
71. Anguilla anguilla (Linnaeus, 1758) + + +          
Godidae                
72. Lota lota (Linnaeus, 1758) + +            
Gasterostiedae                
73. Pungitius platygaster (Kessler, 1858) + +            
74. Gasterosteus aculeatus (Linneaus, 1758)     +          
Syngnathidae                
75. Syngnathus nigrolineatus Eichwald, 1831 +              
Poeciliidae                
76. Gambusia affinis holbrooki (Agassiz, 1854)   + +     + + +
Centrarchidae                
77. Lepomis gibbosus (Linnaeus, 1758) + + + + + + + +
Percidae                
78. Stizostendion lucioperca (Linnaeus, 1758) + + +   + + +  
79. Stizostendion volgense (Gmelin, 1788) + +            
80. Perca fluviatilis Linnaeus, 1758                
81. Zingel zingel (Linnaeus, 1758)                
82. Zingel sterber (Siebold, 1758)                
83. Gymnocephalus cernuus (Linnaeus, 1758)                
84. Gymnocephalus baloni Holcik and Hensel, 1974 + +            
85. Gymnocephalus schraetzer (Linnaeus, 1758) + +            
Gobiidae                
86. Neogobius melanostomus Pallas, 1811* +              
87. Neogobius cephalarges Pallas, 1811* +              
88. Neogobius kessleri Guenther, 1861 + +            
89. Neogobius fluviatilis Pallas, 1811* + +            
90. Mesogohius gymnotrachelus Kessler, 1857* + +            
91. Proterorhinus marmoratus (Pallas, 1811) + + +     +    
92. Benthophilus stellatus (Sauvage, 1874) + +            
Cottidae                
93. Cottus gobio gobio Linnaeus, 1758     +          
94. Cottus gobio haemusi Marinov and Dikov, 1986   +            

Note: * = Their presence has yet to be confirmed

Appendix 2. Composition of the Ichthyofauna in Bulgaria's Black Sea Tributaries and Coastal Lakes.

Origin Column Key: 1= Freshwater; 2= Ponto-Caspian Relict; 3= Boreal-Atlantic Relict; 4= Mediterranean Immigrant

Species Tributaries Lakes Origin
Permanent Temporary Permanent Temporary
1 2 3 4 5 6
Squalidae          
Squalus acanthias Linnaes, 1758       + 3*
Acipenseridae          
Huso huso (Linnaes, 1758)       + 1
Acipenser stellatus Pallas, 1771       + 1
Acipenser gueldenstaedti Brandt, 1833       + 1
Clupeidae          
Sprattus sprattus phalericus Risso, 1810       + 3
Alosa pontica pontica (Eichwald, 1838)   +   + 2
Alosa caspia nordmani (Antipa, 1906)   +   + 2
Alosa caspia balgarica (Drensky, 1934)   +     2
Clupeonella cultriventris (Nordamn, 1840)   +     2
Engraulidae          
Engraulis encrasicholus ponticus Alex., 1927   +   + 4
Salmonidae          
Salmo trutta fario Linnaeus, 1758 +       1
Salmo gaerdneri irideus Gibbons, 1855 +       1
Salmo trutta labrax Pallas, 1811   +     3
Anguillidae          
Anguilla anguilla Linaeus, 1758   +   + 3
Esocidae          
Esox lucius Linnaeus, 1758 +   +   1
Cyprinidae          
Rutilus rutilus (Linnaeus, 1758) +   +   1
Rutilus frisii (Nordm., 1840) +       1
Leuciscus cephalus (Linnaeus, 1758) +   +   1
Leuciscus borysthenicus (Kessler, 1859) +       1
Tinca tinca (Linnaeus, 1758) +   +   1
Scardinius erythrophthalmus (Linnaeus, 1758) +   +   1
Aspius aspius (Linnaeus, 1758) +       1
Leucaspius delineatus (Heckel, 1843) +   +   1
Chalcalburnus chalcoides (Gueldenstaedti, 1772) +   +   1
Alburnus alburnus (Linnaeus, 1758) +   +   1
Alburnoides bipunctatus (Bloch, 1782) +       1
Blicca bjoerkna (Linnaeus, 1758) +       1
Vimba vimba tenella (Nordm., 1840) +   +   1
Rodeus sericeus amarus Bloch, 1782 +   +   1
Gobio gobio gobio Linnaeus, 1758 +   +   1
Barbus meridionalis petenyi Heckel, 1847 +       1
Barbus tauricus Kessler, 1877 +       1
Cyprinus carpio Linnaeus, 1758 +   +   1
Carassius carassius (Linnaeus, 1758) +   +   1
Carassius auratus gibelio (Bloch, 1782) + + +   1
Hypophthalmichthys molitrix Valenciennes, 1844   + +   1
Ctenopharingodon idella Valenciennes, 1844   + +   1
Cobitidae          
Cobitis taenia Linnaeus, 1758 +       1
Cobitis peshevi Sivkov and Dobrovolov, 1986 +       1
Misgurnus fossilis Linnaeus, 1758       + 1
Siluridae          
Silurus glanis Linnaeus, 1758 +   +   1
Gadidae          
Gaidropsarus mediterraneus (Linnaeus, 1758)   +   + 4
Merlangus merlangus euxinus (Nordm., 1840)   1   1 3
Gasterosteidae          
Pungitius platygaster (Kessler, 1859) +   +   2
Gasterosteus aculeatus Linnaeus, 1758 +   +   3
Syngnathidae          
Syngnathus nigrolineatus Eichwald, 1831 +   +   4
Syngnathus typhle argentatus Pallas, 1811   + +   4
Syngnathus abaster Risso, 1810     +   4
Syngnathus schmidti Popov, 1928   +     4
Nerophis ophidion (Linneaus, 1758)   + +   4
Hyppocampus ramulosus Leach, 1814     +   4
Poecilidae          
Gambusia affinis holbrooki (Agassiz, 1854) +       1
Mugilidae          
Mugil cephalus Linnaeus, 1758   +   + 4
Liza aurata Risso, 1826   +   + 4
Liza saliens Risso, 1826   +   + 4
Atherinidae          
Atherina mochon pontica Eichwald, 1831   +   + 4
Atherina hepsetus Linnaeus, 1758       + 4
Serranidae          
Morone labrax (Linnaeus, 1758)   +     4
Centratchidae          
Lepomis gibbosus (Linnaeus, 1758) +   +   1
Percidae          
Perca fluviatilis (Linnaeus, 1758) +   +   1
Stizostedion lucioperca (Linnaeus, 1758) +   +   1
Pomatomidae          
Pomatomus saltatrix (Linnaeus, 1758)   +   + 4
Carangidae          
Trachurus mediterraneus ponticus Aleev, 1956   +     4
Sparidae          
Diplodus anularis Linnaeus, 1758   +   + 4
Centracantidae          
Spicara smaris (Linnaeus, 1758)   +   + 4
Mullidae          
Mullus barbatulus ponticus Essipov, 1927   +   + 4
Labridae          
Symphodus cinereus Bonnaterre, 1788   +   + 4
Crenilabrus ocellatus (Forscal, 1775)   +   + 4
Crenilabrus tinca (Linnaeus, 1758)   +      
Crenilabrus quinquemaculatus (Bloch, 1792)   +     4
Blennidae          
Blennius pavo Risso, 1810     + + 4
Blennius sanguinolentus Pallas, 1811     + + 4
Blennius tentacularis Brunnich, 1768       + 4
Blennius sphinx Valanciennes, 1836       + 4
Blennius zvonimiri Kolombatovic, 1892     +   4
Ophidiidae          
Ophidion rochei Muller, 1845   +   + 4
Ammodytidae          
Gymnammodytes cicerellus Rafinesque, 1810       + 4
Scombridae          
Scomber scombrus Linnaeus, 1758       + 4
Cybiidae          
Sarda sarda (Bloch, 1793)       + 4
Triglidae          
Trigla lucerna Linnaeus, 1758       + 4
Scorpanidae          
Scorpaena porcus Linnaeus, 1758       + 4
Trachinidae          
Trachinus draco Linnaeus, 1758   +     4
Uranoscopidae          
Uranoscopus scaber Linnaeus, 1758   +     4
Gobiidae          
Aphia minuta (Risso, 1810)     +   4
Pomatoschistus minutus (Pallas, 1767)     +   4
Pomatoschistus microps (Kroer, 1837)     +   4
Knipowitschia caucasica Kawrajsky, Berg, 1916 +   +   4
Gobius niger Linnaeus, 1758   + +   4
Gobius ophiocepholus Pallas, 1811   + +   4
Neogobius melanostomus Pallas, 1811 +   +   2
Neogobius platyrostris Pallas, 1811     +   2
Neogobius cephalarges Pallas, 1811   + +   2
Neogobius syrman Nordm., 1840   + +   2
Mesogobius gymnotrachelus Kessler, 1857 +       2
Mesogobius batrachocephalus Pallas, 1811   + +   2
Neogobius fluviatilis Pallas, 1811 +       2
Proterorhinus marmoratus (Pallas, 1811) +   +   2
Benthophiloides brauneri Bell. and Illin.       + 2
Bothidae          
Psetta maeotica (Pallas, 1811)   +   +  
Pluronectidae          
Platichthys flesus luscus (Pallas, 1811)   + +   3
Soleidae          
Solea lascaris nasuta (Pallas, 1811)   + +   4

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