Optimising spawning conditions and growth performance of larvae and juveniles in Barbus altianalis (Boulenger, 1900)
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Barbus altianalis is an indigenous cyprinid that lives in lacustrine-riverine environments with limited distribution to Upper Victoria Nile and lakes Victoria, Edward, George and their associated rivers. The species is a delicacy in Uganda and surrounding regions and also vulnerable to overexploitation. B. altianalis is cultured by very few farmers and the biggest challenge has been lack of seed for its commercial propagation. This study was conducted to determine optimal spawning conditions, larval weaning, juvenile growth and survival with a view of producing mass quality seed for propagation. Two field and 17 lab/pond experiments were conducted to improve hatchability, growth and survival of larvae and juveniles. Results showed that fish for spawning is best picked at ≥ 30-34.9 cm and 35-39.9 cm fork lengh for males and females, respectively. Fish treated with African catfish pituitary extracts (ACPE) performed slightly better than those treated with Dagin. However, the differences between females treated with ACPE and Dagin were not significant with respect to working fecundity (2314.40; 1207.37), fertilisation rates (80.27; 40.80%) and hatchability (42.20; 27.44%) at p > 0.0167 respectively. ACPE are equally effective and cheaper for inducing B. altianalis to spawn. Working fecundity and hatchability were significantly higher when only ripe running females were stripped after 4 hours (100 degree hours) of flashing water than those stripped after 10hrs (250 degree hours) at 25⁰C. Optimal temperature for embryo hatchability was 24⁰C - 27⁰C. Hatchability was good and the same (p > 0.05) between re-circulating (84.3%) and glass tank systems (80.3%). High larval growth (158.61 ± 1.56; 195.03 ± 2.71mg) and survival (81.24 ± 1.55%; 78.96 ± 2.04%) were attained at 30⁰C and 27⁰C, respectively. The digestive tract of B. altianalis was simple and valveless and was on average 2.22 ± 0.37 times longer than its body length. It showed a strong ability to utilize and assimilate every diet but also showed preference of food items at early stages becoming all inclusive in its diet as it matures. Larval ontogeny of digestive structure and related enzyme activity confirmed that microdiets were acceptable at exogenous feeding (6-7 Day after hatch-DAH). But better growth and survival were obtained with a combination diet (Moina + microdiet). Hence, outdoor larvae nursing and microdiet manipulations for better growth and survival were successful at ≥ 15 DAH. When prevalence of aquatic parasites was anticipated, outdoor nursing and or stocking were delayed until after or during larvae scalation process at 48 - 75 DAH. This study has now been able to determine the optimal spawning and growth performance conditions of larvae and juveniles in B. altianalis and it will now be possible to produce mass and quality seed for propagation.