New formulated diets for Solea senegalensis broodstock: Effects of parental nutrition on biosynthesis of long-chain polyunsaturated fatty acids and performance of early larval stages and juvenile fish

Senegalese sole is considered a species with high interest for aquaculture diversification in the South of Europe whose production has shown an important increase in recent years. However, broodstock nutrition of this species is still based on a diet of fresh feeds, which poses important sanitary risks, has variable supply and nutritional composition and contributes to the deterioration of water quality. This study was performed to test two new specifically formulated semi-moist diets for Solea senegalensis broodstock: a control diet (CTR) formulated with high quality ingredients and a further supplemented diet (PLUS), fortified with lipids, vitamins and long-chain polyunsaturated fatty acids (LC-PUFA), mainly DHA. Larvae originating from simultaneous spawns of both broodstock groups were reared in the same standard conditions up to 67 days post-hatching (dph) and effects were assessed on early ontogeny (up to first-feeding), larval (up to 17 dph) and juvenile performance. Both diets led to the production of eggs with good viability, hatching rate and fatty acid composition. The fatty acid profile reflected differences in the experimental diets, with eggs from the PLUS group presenting higher levels of both EPA and DHA, although more markedly for EPA. Furthermore, significant differences in the percentage of EPA were maintained until 7 dph, while DHA was only significantly higher in eggs and 0 dph larvae from the PLUS treatment. The expression of enzymes of the LC-PUFA biosynthesis pathway was assessed in parallel and results show that transcript levels of elovl5 and Delta 4fad in eggs and newly hatched larvae were affected by broodstock diet and that DHA biosynthesis capacity of Senegalese sole larvae may have been up-regulated at hatching in the CTR treatment. Further nutrient supplementation in the PLUS diet did not enhance larval survival and performance and larvae originating from this treatment were significantly smaller than their CTR counterparts at hatching and 3 dph and had lower growth up to 17 dph, probably reflecting variations in egg size between batches. However, after metamorphosis, post-larvae from the PLUS treatment quickly caught-up and after complete weaning were significantly larger than juveniles originating from the CTR broodstock. Furthermore, juveniles from the PLUS treatment had a much lower incidence of tail fin deformity. These results were surprising and should be further investigated as, although we cannot exclude a genetic effect, the results could also indicate a nutritional programming effect of broodstock diet in sole juvenile growth and quality. In addition, the results suggest that Senegalese sole larvae are capable of regulating DHA biosynthesis as early as at hatching to counterbalance lower levels of DHA in eggs. Finally, we demonstrate that the current feeding protocol of sole broodstock can be replaced by a safer formulated semi moist diet with good results. (C) 2014 Elsevier B.V. All rights reserved.