Commercial micro diets and weaning strategies influence immunity-related gene expression in bluefin bream (Sparidentax hasta)

Use of microdiet (MD) in hatchery operations is becoming popular in the background of factors such as high dependence on live food, variabilities in their quality in terms of nutritive values , suitability, particle size variation, and probabilities of carrying and transferring pathogens. Arabian sobaity bream ( Sparidentax hasta ) fry was weaned using four commercial microdiets (MDs), designated at MDA, MDB, MDC and MDD, to evaluate their efficacy in sustaining survival and growth which formed the basis for selecting the best microdiet (MDA) and for evaluating weaning schedules. This part of the study focuses on the immune gene expression vis-à-vis MDs and weaning schedules. Weaning with MDA was consistently better in enhancing the expression of innate immunity genes. The highest relative expression was in MDA-weaned larvae (10 %) for the antiviral Mx gene. Gradual weaning schedules with MDA was the best when weaned from 14 dph. Early weaning (from 8 and 10 dph) produced significantly lower survival and reduced relative immune gene expression than that of the delayed weaning (12 and 14 dph). Abrupt weaning with any of the MDs significantly reduced survival rates and resulted in the down regulation of most of the genes. Lysozyme (LYS) and Alkaline phosphatase (ALP) were significantly downregulated when weaned early or abruptly. • Microdiets in bluefin bream larvae reduced dependence on live food. • Co-feeding with the weaning diet from 14 dph was the best for the bluefin bream larvae. • Co-fed larvae showed on-par survival and higher immune gene responsiveness compared to live food-fed larvae.