Reproductive biology of the fish Labeobarbus intermedius in the Dirma and Megech tributary rivers of lake Tana (Ethiopia)

Abstract

Spawning habits of Labeobarbus intermedius were studied from samples collected on the river mouths of Dirma and Megech, tributaries of Lake Tana, during December 2003 to November 2004. Fish were caught using 6, 8. 10 and 12 cm stretched mesh size gill nets. In the monthly samples. fish with reproductively mature and immature gonads were captured. Nevertheless, breeding fish were more frequent in the catch and gonadosomatic index (GSI) values peaked from August to November for both sexes. Fulton 's condition factor was also significantly lower during these months (Mann-Whitney U test; P<0.001 ). These reproductive parameter variations indicate that L. intermedius reproduces throughout the year, but. it reproduces intensively from August to November. The sex ratio was 1 :3.01 {male: Female) and significantly different (X² : P<0.001 ). Length at maturity was 22.57 cm for females. The mean fecundity was 3588 eggs (ranged between 1761 and 8367 eggs) per female. Mean ova diameter was 1.99 mm· (ranged between 1.65 to 2.30 mm). There was exponential relationship between fecundity (F) and fork length (FL) (FL=0.2691FL³ , r²=0. 75) while fecundity and gonad weight were related linearly (GW) (F=216.56GW-160.45. r²=0.95). Polynomial relationship was observed between fecundity and total weight (TW) (F=0.0016TW² + 19.769TW + 240.15, r²=0. 78). Closing the gill net commercial fishery in these river mouths throughout the year or at least from August to November is strongly recommended to prevent recru itment over fishing on L. intermedius in Lake Tana.

Keywords: Fecundity, Gonad maturity, Sex-ratio, Spawning migration , River mouths.