Age of weaning impacts the growth performance, intestinal morphology and gene expression of the tambaqui Colossoma macropomum larvae

Abstract Fish larvae feeding management represents one of the critical points for survival and aquaculture success. The larvae of many fish species require live feeds during early development, typically before being transitioned to formulated feeds through a process known as weaning. Despite the importance of tambaqui ( Colossoma macropomum ) , to Brazil’s aquaculture industry, the optimal timing for weaning and its effects on larval development remain unclear. Therefore, we evaluated different weaning ages in tambaqui larvae reared in a recirculating aquaculture system to identify the optimal timing for feed transition. The larvae were initially fed Artemia nauplii and weaned at 12 (W12), 15 (W15), 18 (W18), 21 (W21), and 24 (W24) Days After Hatching (DAH), and then evaluated for their growth performance, intestinal morphology and trypsin , pepsin and hsp70 gene expression. The larvae that were weaned early (W12 and W15) had reduced zootechnical performance and greater expression of the hsp70 gene, indicating stress. Trypsin expression was detected only after weaning, with the highest levels recorded in W18, W21, and W24, while pepsin was expressed in all treatments, albeit at relatively low levels in W12. Larvae weaned at 24 DAH showed higher growth and digestive gene expression but greater size heterogeneity, whereas larvae weaned at 21 DAH exhibited better intestinal mucosal fold development, higher survival, and greater stock uniformity. Overall, weaning at 21 DAH provided a more balanced outcome among the evaluated parameters, representing a likely strategy for the production of high-quality tambaqui fingerlings.