Impact of early life rearing conditions on feed intake, growth, nutrient digestion and energy metabolism of Nile tilapia in later life

Early life rearing conditions have significant impact on the microbial colonization, survival, and growth of fish larvae. However, the long-term effects of early life rearing conditions on how fishes adapt to changing environments, as well as how nutrient digestion and energy metabolism are affected during later life stages, remain largely unknown. In this study, hatched Nile tilapia larvae were cultured for six weeks in three distinct microbial conditions, i.e. a flow-through system (FTS), a recirculating aquaculture system (RAS) and a RAS with supplementation of the probiotic Bacillus subtilis in the feed (RASB) (Phase I). At the end of phase I, all fish were transferred to one new common RAS environment and reared for another six weeks (Phase II). Subsequently, fish from each early life treatment group were fed for another five weeks at 40 %, 75 % and 100 % of satiation, to determine the apparent digestibility coefficient and energy requirement for maintenance (Phase III). Results showed that fish larvae cultured during Phase I in RAS grew faster than larvae cultured in FTS once transferred to the new common RAS environment (Phase II). Early life rearing conditions had a short-term impact on fish body composition (e.g. energy and crude fat) after six weeks co-culture in the new common RAS environment at the end of Phase II. However, no long-term effects on the digestibility of macronutrients, on the nitrogen and energy balances, and on the digestible energy requirement for maintenance were observed during Phase III. Despite that, fishes reared in the RASB microbial environment at the start of this study, consistently reached the highest average body weight during all three experimental phases, and showed higher maximum feed intake and energy efficiency during Phase III. Overall, early life microbial rearing conditions of Nile tilapia had a short-term impact on fish growth and fish body composition, and a long-term impact on feed intake at ad libitum feeding even after being cultured for eleven weeks under similar conditions.