Influence of the timing of weaning on growth and survival of juvenile winter flounder (Pseudopleuronectes americanus)

Metamorphosis is a critical developmental stage that presents particular challenges in fish aquaculture. The sharp increase in mortality that accompanies this transformation has often been attributed to nutritional deficiencies. Providing live feed (the rotifer Brachionus plicatilis Müller, 1786 and the brine shrimp Artemia salina (Linnaeus, 1758)) during the larval stages is costly and labour intensive, which explains why much effort has been put on early weaning. However, previous observations in winter flounder (Pseudopleuronectes americanus (Walbaum, 1792)) indicate that juveniles weaned after settlement had better survival than those weaned at the larval stage. In this study, we tested whether late weaning (at settlement (W0) and groups maintained on co-feeding for 1 month (W1), two months (W2), or 3 months (W3) after settlement) could improve juvenile survival and lipid composition. Our results demonstrated that maintaining co-feeding beyond the larval stage was essential for after-settlement survival. Juveniles co-fed until 90 days after settlement were 32.5% heavier. Analyses of fatty acid trophic markers suggested that juveniles preferentially fed on enriched rotifers rather than inert food. No pigmentation or fin erosion problems were observed in any of the weaning treatments, which indicates good rearing conditions.