Effects of wild zooplankton versus enriched rotifers and Artemia on the biochemical composition of Atlantic cod (Gadus morhua) larvae

Diet at start feeding can affect fish development, pigmentation and growth, and live feed can provide all the dietary requirements of larvae. Enriched rotifers and Artemia are normally used as live feed in the first stages of commercial larval production, however, wild zooplankton or copepods provide better results. The goal of this study was to evaluate whether supplementing enriched rotifers and Artemia (RA) with fish protein hydrolysate (RA-PH) or a small amount of wild zooplankton (RA-Zoo; 5-10% of total prey items) would improve the nutritional quality of larval cod (Gadus morhua), and how it correlated with larval growth rates. Wild zooplankton had significantly higher proportions of the polyunsaturated fatty acids 22:6ω3 (DHA, 23%) and 20:5ω3 (EPA, 11%). Larvae fed wild zooplankton also had higher proportions of essential omega-3 fatty acids (43% RA-Zoo; ≈ 39-40% RA/RA-PH) and much higher EPA/ARA ratios compared to those only fed with enriched rotifers and Artemia or these prey items plus protein hydrolysate (≈ 4 RA-Zoo; ≈ 1.3-3 RA/RA-PH). Further, these fatty acid proportions correlated significantly with larval growth rates and improved fish development. Based on these results, we recommend the inclusion of small amounts of wild zooplankton or commercially produced copepods with high proportions of DHA and EPA, and low proportions of ARA, in the initial diet of Atlantic cod larvae.