Finfish broodstock nutrition and impacts on reproductive output in Atlantic Cod (Gadus morhua)

Webb, Matthew (2014) Finfish broodstock nutrition and impacts on reproductive output in Atlantic Cod (Gadus morhua). Masters thesis, Memorial University of Newfoundland.

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Abstract

In aquaculture, broodstock nutrition is recognized as an influential factor affecting spawning performance and subsequent egg and larval quality. The purpose of this thesis was to examine broodstock dietary effects on the eggs of fish fed different experimental diets. This study also examined broodstock dietary effects on larval growth using RNA:DNA as predictors of growth. Three diets were tested: an OG diet, an experimental BR diet and a BF diet. The first objective of this work was to categorize the dietary lipid classes and fatty acids in the eggs produced by the broodstock fed these diets. Significant differences were observed between five of the nine dietary lipid classes examined and significant differences were observed in fatty acids (% of total FA) and their ratios among diets for 16 of the 29 dietary fatty acids examined. Of particular importance are, TAG (p = <0.001), PL (p = <0.001), EPA (p = <0.001), DHA:EPA (p = <0.001) and EPA:ARA (p = <0.001). The BF diet which showed the best reproductive output in terms of fertilization and hatching success had the highest proportions of DHA:EPA and the lowest proportions of TAG and EPA. Overall, the differences present in the dietary lipid classes of this study did not translate into differences in the lipid classes of the eggs. Dietary differences were more evident in the essential FA composition of diets and eggs as the proportions of DHA and EPA in the eggs are reflective of the dietary proportions. However, the proportions observed in the eggs are much higher, and the DHA proportions are larger than the EPA proportions, supporting the idea that DHA is preferentially retained in developing yolk-sac larvae. The second objective was to determine if the experimental diets led to any growth benefits in the subsequent larvae. No effects of broodstock diet were observed in larval survival, concentration of nucleic acids, protein concentration or SGR of larvae. The slopes of the RNA:DNA (p = <0.001) after 7 dph showed a significant difference indicating that the slope of the BR group was significantly lower than the other two groups but this difference did not translate into differences in growth . These results suggest that, although larvae originating from parents fed the BF and OG diets have a higher growth potential (as inferred by the RNA:DNA) when compared to the larvae originating from broodstock fed the BR diet, they grow similarly (up to 49 dph). We found a lack of correlation between the RNA:DNA and growth rates contradicting some of the findings of other authors and questioning the accuracy of RNA:DNA as an indicator of growth in this situation. Our results suggest that the BR diet may improve reproductive performance, when compared to the OG diet, although the BF diet remains the golden standard for optimizing broodfish reproductive output.

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