Spawning Migration and Reproductive Biology of Labeobarbus (Cyprinidae: Teleostei) of Lake Tana to Dirma and Megech Rivers, Ethiopia
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Date
2005-06
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Addis Ababa University
Abstract
The reproductive biology of the endemic ‘large’ Barbus (renamed Labeobarbus) species was studied from
December 2003 to November 2004 in Dirma and Megech affluent rivers of Lake Tana. Fish and other
environmental parameters were sampled monthly from November to June, bimonthly in July and weekly
from August to October at the river mouths. Similarly, the spawning migration to upstream reaches of
these rivers was monitored weekly in the peak breeding season (August to October) using 6, 8, 10, 12
stretched mesh size multi-filament and multi-mesh monofilament gillnets, fykes, local basket traps and
hook-and-line fishing gears. Samples of fish caught were identified, measured, weighed, dissected and
sexed. Changes in mean gonado-somatic index, Fulton’s condition factor and relative abundance of each
particular Labeobarbus species were analyzed seasonally. Peak spawning generally occurred from August
to October. Six species (L. brevicephalus, L. intermedius, L. megastoma, L. tsanensis, L. truttiformis and L.
surkis) formed aggregation in the river mouths. The first species to congregate was L. megastoma,
followed by L. tsanensis and L. truttiformis and the final were L. brevicephalus and L. surkis. Macrospatial
segregation among these species between the two river mouths did not occur, however, except L.
intermedius, temporal segregation was apparent in the river mouths in the spawning season. All these
species, except L. surkis, that congregate in the river mouths ascend to upstream reaches of the rivers.
This spawning run showed sequential patterns of segregation among the migrating Labeobarbus species. L.
truttiformis and L. tsanensis were the first to migrate up rivers and L. megastoma just run next to them,
however, L. brevicephalus was the last in the sequence of migration. Excluding the running (egg shedding)
individuals, mean absolute fecundity and egg diameter of L. truttiformis, 4563 eggs and 1.99 mm,
respectively, were higher than L. brevicephalus (2421 eggs and 1.97 mm) but their relative fecundity
remained the same. The relationships of absolute fecundity with fork length, body weight, and gonad
weight were curvilinear. Length-weight relationships were curvilinear and in agreement with the cube law.
Based on the results obtained in this study and previous investigations in other affluent rivers, the Lake
Tana Labeobarbus spawning strategies are hypothetically categorized into three: (1) obligate riverine
spawners (L. brevicephalus, L. tsanensis, L.truttiformis), (2) generalists (spawning in the rivers and in
Lake Tana) (L. acutirostris, L. intermedius, L. macrophtalmus, L. megastoma, and L. platydorsus), and (3)
lacustrine spawners (L. crassibarbis, L. dainellii, L. gorgorensis, L. gorguari, L. longissimus, L. nedgia,
and L. surkis). Generalists and lacustrine spawners most probably spawn in the littoral and adjacent
floodplains of Fogera and Dembea; however, their actual breeding ground should be investigated to
implement sound management options. To sustain the riverine Labeobarbus spawners, closing the gillnet
fishery from August to October in the rivers and river mouths is believed to be necessary.
Keywords: endemic, fecundity, Labeobarbus, Lake Tana, reproduction, spawning migration
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Keywords
endemic, fecundity, Labeobarbus, Lake Tana, reproduction, spawning migration