A Little Goes a Long Way: Improved growth in Atlantic cod (Gadus morhua) fed small amounts of wild zooplankton

We examined the effects of partial dietary supplementation with wild zooplankton or fish protein hydrolysate on cod production traits, and how they related to the expression of growth and appetite regulating transcripts and muscle cellularity. Atlantic cod larvae were fed three different diets: enriched rotifers and Artemia (RA); RA+fish protein hydrolysate (RA-PH); and RA supplemented with 5–10% wild zooplankton (RA-Zoo). Partial supplementation with zooplankton significantly improved cod dry weight at 60days post-hatch (by approximately 4-fold), specific growth rate (by 2.5% day−1) and the general development of cod larvae. Although the zooplankton fed cod were still larger at approximately 1.5years of age, the growth advantage of this group decreased with age (the difference in wet mass decreasing from approximately 30% at 0.5years old to 11% at 1.5years old). In contrast, the protein hydrolysate enrichment did not improve growth, had a negative effect on survival, and increased the incidence of external deformities in 1.5year old fish. The growth enhancement observed in the RA-Zoo larvae was largely unrelated to differences in the transcript levels of several important growth [Insulin-Like Growth Factor 1 (igf-1); igf-2; Growth Hormone (gh); GH Receptor-1 (ghr-1); ghr-2; and myostatin (mstn)] or appetite regulating genes [Cocaine and Amphetamine Regulated Transcript (cart) and Neuropeptide Y (npy)], but was associated with an increase in the number and size of skeletal muscle fibers. Our findings suggest that incorporating small amounts of wild zooplankton into larval feeding regimes may significantly enhance the production of marine fishes, but that the transcript levels of the above hormones and hormone receptors are not valuable biomarkers of growth in cod larvae.This research shows that small amounts of zooplankton significantly improve the growth of Atlantic cod larvae, and thus, that cultured zooplankton may be a viable and cost-effective strategy for increasing the growth (and potentially health) of intensively cultured marine finfishes.