Reproductive biology of Protopterus aethiopicus in Lake Bisina, Uganda and performance of Larvae under experimental diet

Abstract

Protopterus aethiopicus (Heckel, 1951) is an important food fish due to its meaty and taste qualities. It is an air breather and can survive desiccation of its habitat and low dissolved oxygen levels. Its population is declining in Uganda due to over exploitation, environmental degradation and large scale conversion of wetlands to agriculture and settlements. Aspects of reproductive biology of P. aethiopicus in Lake Bisina, Kumi district, Uganda were investigated from October 2015 to March 2016, and performance of larvae reared from wild spawned eggs and fed on different diets was examined in experimental glass tanks for 28 days. The study aimed at improving conservation strategies for P. aethiopicus in the wild, and to advance knowledge towards captive breeding of the species. A total of 605 fish of body length 8cm to 124cm TL (mean 38.66 ± 14.16cm) and body weight 14g to 6660g (mean 241.78 ± 72.12g) were used for this study. The sex ratio was 1:0.704 males to females and statistically significantly different from the 1:1 expected ratio (X2 = 18, df = 1, P < 0.05 n = 605). Males attained 50% maturity at 26.54 cm TL, females at 22.39 cm TL. Size limit for harvest in the wild was established to be 30cm. Total fecundity ranged from 564 to 19,570 eggs (mean = 5330 ± 841.32 SD) in fish measuring 387g to 2020g TW (mean = 793.83 ± 125.3 SD). The mean relative fecundity was 7 eggs per gram. There was a significant positive linear relationship between fecundity and total length (y=503.1x – 27377; R2 = 0.909; p=0.01) and between total weight (y=11.59x – 3876; R2 = 0.964; p=0.01). The overall mean condition factor ranged from 0.09 to 1.58 (mean = 0.31± 0.16) and for separate sexes 0.09 to 1.40 (mean = 0.31 ± 0.15) in males and 0.18 to 1.58 (mean = 0.31 ± 0.17) in females and was not statistically significantly different (t = 0.863 p = 0.723). Survival after 28 days of culture was higher for larvae fed on a combination of artificial dry feeds and live feed-moina (77%) than that fed separately on live feed-moina (71%) and artificial dry feed (66%). The results reveals that larval co-feeding on live and inert feeds favors the growth performance for P. aethiopicus. Conclusively, the harvest size limit of 30cm should be included in the national regulations for capture fisheries of P.aethiopicus. Secondly, further research towards artificial induction of P.aethiopicus to spawn in activity warrantee further research, given the high survival of larvae registered in this study.