A little goes 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 supplementedwith 5-10% wild zooplankton (RA-Zoo). Partial supplementation with zooplankton significantly improved cod dry weight at 60 days 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 1.5 years of age, the growth advantage of this group decreased with age (the difference in wet mass decreasing from approximately 30% at 0.5 years old to 11% at 1.5 years 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 1.5 year old fish. The growth enhancement observed in the RAZoo 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. (C) 2015 Elsevier B.V. All rights reserved.