How Decapsulated Artemia parathenogenetica Cysts and Microdiets Influence the European Seabass Larvae Weaning, Growth, and Oxidative Stress

A study on the weaning of the European seabass larvae (Dicentrarchus labrax) from 37 to 62 days post-hatching (dph) was conducted. The 37 dph larvae were stocked at the Fish Nutrition Lab, Aquaculture Division, Alexandria, NIOF. In the GAFERD Km21 marine hatchery, larvae were reared and fed enriched rotifers and Artemia in the same tank from 3 to 37 dph. Growth performance (larval length and weight), condition factor, survival percentage, catalase (CAT), total antioxidant capacity (TAC), superoxide dismutase (SOD), and several hepatic enzymes were evaluated at these critical larval stages following the introduction of five treatments in triplicates: live Artemia franciscana (LArt), local dried decapsulated Artemia parthenogenetica (DArt), Vitellus (V), Shaimaa Hebalah microdiet (SH), and INVE Orange® (O) microdiet. At 62dph, early weaned Dicentrarchus labrax larvae that consumed DArt exhibited significantly greater (P< 0.05) length and weight growth performance. Larvae that consumed LArt demonstrated higher survival rates, while those fed SH and O microdiets showed better condition factors than other weaning microdiets. Larvae fed O microdiet showed the highest levels of glucose, triglycerides, alkaline phosphatase (ALP), acid phosphatase (AP), and alanine aminotransferase (ALT) activities. In contrast, larvae fed DArt exhibited the highest levels of albumin and SOD activities. Larvae fed SH microdiet exhibited the best protein content, globulin, aspartate aminotransferase (AST), SOD, and total CAT activities (P< 0.05). Notably, TAC activities were significantly higher in larvae that consumed the LArt microdiet. In terms of fatty acids, larvae fed SH microdiet had the highest levels of arachidonic acid (ARA, C20:4), docosahexaenoic acid (DHA, C22:6), highly unsaturated fatty acids (HUFA), and n-3 long-chain polyunsaturated fatty acids (LCPUFA%). Larvae fed DArt, V, and SH microdiets had the highest levels of eicosapentaenoic acid (EPA, C20:5), while those fed DArt and V showed the highest significant EPA/ARA ratios. Additionally, larvae fed LArt, DArt, V, and SH microdiets exhibited the highest n-3/n-6 ratios. In conclusion, the European seabass larval weaning, growth, survival, antioxidant capacity, and fatty acid profiles in larvae fed local microdiets (SH and DArt) showed results comparable to high-quality, internationally available microdiets. This finding is a promising step forward for the development of Egypt's marine hatchery industry.