Experimental evidence of fatty acid limited growth and survival in Pacific cod larvae

Abstract

Changing environmental conditions in the North Pacific are altering the lipid/fatty acid (FA) composition of zooplankton assemblages, but the consequences to resident fish larvae are unknown. In the laboratory, we reared Pacific cod Gadus macrocephalus larvae over 4 wk on prey enriched with varying levels of 2 essential FAs (docosahexaenoic acid, DHA, In the laboratory, we reared Pacific cod Gadus macrocephalus larvae over 4 wk on prey enriched with varying levels of 2 essential FAs (docosahexaenoic acid, DHA, 22:6ω-3, and eicosapentanoic acid, EPA, 20:5ω-3) to determine how this species responded to such changes in prey quality. Ratios of DHA:EPA were chosen to represent the natural variation observed in zooplankton of the North Pacific. We tested the hypotheses whether (1) energetically similar diets comprised of varying levels of DHA and EPA affect growth and survival in Pacific cod larvae, and (2) the highest levels of DHA:EPA (2:1) are optimal for Pacific cod larvae, as it has been shown for Atlantic species. Pacific cod larvae grew fastest with diets containing high levels of ω-3 polyunsaturated fatty acids (PUFA > 22%). Diets with the same total lipid content but different DHA:EPA ratios (>0.1:1 to 2:1) also mediated growth and lipid composition of the larvae. Unlike Atlantic cod, Pacific cod larvae did not show as high a requirement for DHA relative to EPA but rather achieved largest size-at-age with intermediate DHA:EPA ratios (0.8:1 to 1.1:1). This range most closely resembled DHA:EPA ratios reported from North Pacific copepods, suggesting anomalous years with an over-or under-abundance of DHA-rich dinoflagellates or EPA-rich diatoms may be detrimental to survival and growth of Pacific cod larvae in the field. © Inter-Research 2010, www.int-res.com.