Effect of dietary essential fatty acids and vitamins on egg quality in turbot broodstocks

Varying egg quality is one of the main factors interfering with the reliabl e performance of marine fish hatcheries. As larval performance during the f irst period largely depends on the availability of essential nutrients, the endogenous provision of these nutrients through the egg stages, and possib ly parental diet, might be an important tool in improving hatchery output. Therefore, several feeding experiments were conducted on turbot (Scophthalm us maximus) broodstock reared under production conditions at two commercial facilities in France: France Turbot (FT) and Sepia Conseil (SC). Diets var ied mainly in essential fatty acids (omega-3 HUFA), Vitamins C and E, and w ere fed for 2-3 months prior to the reproductive season. Egg quality parame ters, i.e. fertilization and hatching rate, egg and oil droplet diameter, a nd biochemical composition, were monitored for each female during its total reproductive phase. Egg size during the reproductive cycle showed a low variability among femal es receiving the same treatment, but became significantly smaller as the se ason progressed. The same occurred for the oil globule in the non-vitamin s upplemented groups, whereas it significantly increased in the vitamin-suppl emented groups. However, these observations could not be correlated with an y of the hatching or fertilization characteristics. The egg dimensions also varied as a function of the diet supplied, i.e. high HUFA levels in the br oodstock diet resulted in a significant increase of egg diameter, oil globu le diameter as well as fertilization rate. Interestingly, the control group s, with the lowest fertilization rate, had the highest hatching percentage, significantly higher than the HUFA/non-vitamin enriched groups. Using non-selected sources of trash fish as a food source at SC resulted in low levels of ascorbic acid (AA) in the eggs compared to the administratio n of an optimal quality batch of mackerel at FT. Enrichment of the trash fi sh with ascorbate-2-polyphosphate (ApP) resulted in a tripling of the AA co ntent. Extra enrichment of the FT control diet did not further increase the levels in the eggs, suggesting that a saturation level was obtained. The m ajor fatty acids in turbot eggs as well as freshly hatched larva are 16:0, 18:1 omega-9, 20:5 omega-3 and 22:6 omega-3, but no obvious changes in thei r pattern could be detected for the different broodstock treatments. Howeve r, the level of 20:4 omega-6 was significantly higher in the control group of FT, and showed a high correlation with the hatching percentage of the eg gs obtained from the various broodstock treatments.