Nucleotide enhancement of diets, fish reproduction and egg quality

González Vecino, José Luis (2005). Nucleotide enhancement of diets, fish reproduction and egg quality. PhD thesis The Open University.



Fish reproduction, and egg and larval quality are affected by broodstock nutrition. Nucleotides, the building blocks of DNA and RNA, are now considered as semiessential nutrients during periods of food deficiency, stress, rapid growth and immunological stress. Since oogenesis is a process of intensive cell division with high nucleic acid formation and a concomitant high requirement for nucleotides, broodstock diets were enhanced with nucleotides. Their effects on the reproductive performance of Atlantic halibut (Hippoglossus hippoglossus L.) and haddock Melanogrammus aeglefinus L.), two cold water species with different life histories, were compared with control diets.

Broodstock condition at the end of the spawning seasons did not differ between dietary treatments. However, dietary nucleotides improved total relative fecundity and batch relative fecundity of halibut and haddock respectively. Egg quality was also improved in both species. Fertilisation rate of haddock eggs and hatching rate in halibut and haddock eggs were significantly higher with the nucleotide diets. Nucleotide supplementation resulted in improved larval quality in both species. Survival of halibut larvae at the end of the yolk-sac stage was higher in the nucleotide group. Haddock larval survival five days after hatch was the same in both diets but improved at ten days post hatch as a result of significantly better developed gut and first feeding success in the nucleotide group. Histological examination of fish ovaries at the end of the experiment revealed no differences in the atresia levels.

Nucleotide composition of egg and larval samples did not differ between diets, suggesting that dietary nucleotides were utilised by the broodfish to cover their nutritional requirements during oogenesis and reproduction. The enhanced reproductive performance in the nucleotide group is discussed in relation to a higher lipid mobilisation during oogenesis and quality of the yolk being consequently improved. Energy charge is confirmed as an egg quality indicator.

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