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Fishes are cold blooded aquatic chordates with appendages (when present) developed as fins, whose chief respiratory organs are gills and whose body is usually covered with scales. They are the most diverse in species among vertebrates (backbone animals); there are more than 25,000 described species of fishes in the world.
There are nearly 200 species of fishes recorded from the fresh water systems of Ethiopia. Lake Tana is Ethiopia’s largest lake (about 3500 K.M2)and is situated in the north western highland at an altitude of approximately 1800 masl. There are 28 fish species in Lake Tana out of which 21 are endemic to the country. The most notable genus of the family Cyprinidae in Lake Tana is Labeobarbus. There are 17 species of Labeobarbus forming a unique cyprinid species flock in the world.Nine of the seventeen species are known to be migratory and spawn in the permanent rivers. Gumara, Ribb, Gilgel Abay, Dirma Megech and Arno Garno Rivers and their tributaries are known to be important breeding grounds.
Lake Tana and Belles sub-basins are considered to be growth corridors by the Federal and Regional Governments. Hence several development projects (dam building and irrigation projects) are being studied and/or implemented. These projects may possibly pore serious problem on the water level water quality and biodiversity of Lake Tana and the feeder rivers. The planned dams are also feared to block the vital migration of the fishes and this may ultimately lead to the demise of this unique group of fishes and decline in the fish stock of lake Tana. Some of the other threats to the fish diversity in Lake Tana include Overexploitation of fish resources, Encroachment on the wetlands and shores of the lake, problems in Institutional capacity and linkage and Influx of Affluent. As a result of the above threats, some of the Labeobarbus spp. are recognized as Endangered and some as Vulnerable by the International Union of Conservation of Nature (IUCN). The descriptions of four of such species are provided below:
Labeobarbus acutirostris is a medium sized (maximally 411 mm fork length), shallow (body Depth<head length), and narrow bodied species, sometimes with a slight nuchal hump (in larger specimens). Specimens from 32 to 811 mm fork length have been observed. The head is relatively long and marrow, with a small head depth and a tapering narrow snout. The head inclination is relatively small, with a straight to concave dorsal profile. The eves are relatively large, with a small interorbital width The operculum depth is small. The lower jaw is relatively long and is equal to the upper jaw or protrudes (usually in larger specimens). The oral gape is relatively large and (sub) terminal. The mouth has thin lips, the lower one interrupted or continuous. The barbells are relatively short and thin. The lateral line scale count is on the average 31-36, but the number of scales from the dorsal fin to the lateral line is relatively high (5.5.7), as is the circumference scale count (24-26).
Live specimens are very light, silvery white with a slightly darker (silvery grey) back. The fins are whitish: often the pectoral, and sometimes the caudal fins are tinged pink or red at their bases. In alcohol the light color, with the slightly darker back can still be observed, the basic color being light yellowish brown.
Labeobarbus acutirostris is known from Lake Tana only. It occurs over muddy, sandy and rocky substrates all over the lake, preferably in water deeper than 6 m. Labeobarbus acutirostris is a real piscivore. Specimens smaller than 15cm FL mainly eat zooplankton and insect larvae, but already start feeding on fish. When growing larger the importance of fish in the diet increases rapidly, while zooplankton disappears: the amount of insect larvae decrease. Adult insects are more prominent in the diet of fish larger than 25cm fork length: macrophytes are also sometimes found.
Labeobarbus gorguari is a medium to large sized (maximally 532mm fork length), shallow (body depth<head length) species, with a conspicuous steely rising uncial hump Specimens from 91 to 532mm fork length have been observed. The head relatively long, with a small depth: the snout is of average length and width. The head inclination is relatively small, with a straight to concave dorsal profile. The eyes are a little smaller than average, with an average interorbital width. The operculum depth is also average, with an average interorbital width. The upper and lower jaws are relatively long and the latter is equal to the upper jaw, or extends slightly beyond (usually in larger specimens). The oral gape is large, round and (sub) terminal, with moderately developed lips, the lower one usually continuous. The barbells are relatively short and thin. The lateral line scale count has a range of 29 to 37.
Live specimens are very dark green, dark brown, coppery or blackish red or black Usually, the ventral parts are lighter. The head and fins are generally of the same color as the rest of the body, but often even darker. In alcohol, the very dark color persists, usually becoming dark brown.
Labeobarbus gorguari is known from Lake Tana only. It prefers rock substrate in waterless than 6m deep. especially in the shore areas, but it also occurs over muddy and sandy substrates. Based on the content of 16 intestines, Labeobarbus gorguari has a mixed diet of mainly fish, insects and macrophytes.
Labeobarbus macrophtalmus is a medium sized (maximally 425 mm fork length). species of average body depth (body depth head length) and width, usually with a clear nuchal hump large specimens. Specimens from 53 to 425 mm fork length have been observed. The head inclination is relatively small, with a slightly convex to concave dorsal profile. The eyes are very large, with a small interorbital width. The operculum depth is average. The upper and lower jaws are of average length, the latter being equal to the upper jaw when the mouth is closed or even extending beyond it usually in larger specimens. The oral gape is of average size and sub) terminal. The mouth has thin lips, the lower one interrupted or continuous. The barbells are relatively short and thin The lateral line scale count is ave608rage (30-34, but the circumference wale count is relatives high (23-26)
Live specimen have very yellowish or brownish silvery ground color, dark brown on the back. The fins are brownish, the pectoral sometimes with some dark markings on the edges. In alcohol, the basic pattern of lighter sides and darker back is preserved, the ground color being yellowish brown.
Labeobarbus macrophtalmus is known from Lake Tana only. It occurs all over the lake. over muddy, Nandy and rocky substrates with a slight preference for rocks), usually in water deeper than 3m. Based on the contents of 17 intestines, Labeobarbus macrophtalmas mainly feeds on insects (both larvae and adults), small specimens also eat zooplankton. while larger ones sometimes exclusively feed on fish.
Labeobarbus Osseensis is a small sized (maximum 264mm length), deep-bodied (body depth>head length) species, sometimes with a slight nuchal bump. Specimens from 97to 264 mm standard lengths have been observed. The caudal peduncle is deep. The scale counts on average 32scales on lateral line: 12-14 predorsal scales) are lower than in most other Labeobarbus species. The anal and ventral fins are rather short. The head is rather short and deep with a straight dorsal profile. The upper and lower jaws are short compared to the other species the lower jaw falls within or is equal to the upper jaw when the mouth is closed. The gape is a terminal to inferior and small The most diagnostic character of Labeobarbus osseensis, however, is the structure of the lower jaw, which is stiff, and tapers towards a narrow, hypertrophied distal tip, covered with thick skin. The protruded mouth does not form a cylindrical tube’. like it does in the other Labeobarbus spp. but the tip of the lower jaw extends forward, given it a forceps like appearance.
Live specimens are rather dark greenish brown, the back being darker, with usually greenish. In alcohol the basic color is a dull yellowish brown, the back being darker.
Labeobarbus osseensis is known from the southern parts of Lake Tana only. It especially occurs near rock substrates in water of less than 3 m deep. Labeobarbus osseensis feeds on adult insects and macrophytes.
Source:-Abebe Getahun (Professor), Addis Ababa University.
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