Effect of DHA content in rotifers on the occurrence of skeletal deformities in red porgy Pagrus pagrus (Linnaeus, 1758)

Despite being proposed as a potential candidate for diversification of marine aquaculture, limited larval survival and the occurrence of elevated levels of skeletal deformities restrict the commercial production of red porgy. The present study was conducted to determine the effect of rotifer enrichment, particularly on DHA, on growth, survival and occurrence of skeleton deformities in this species. The study included two trials, in one the viability of commercial emulsions for rotifer enrichment was evaluated whereas in another the effect of the elevation of DHA in rotifer emulsions on the larvae was studied. No significant differences were found in growth between larvae fed different rotifers in both trials suggesting that 1.9% dw DHA is enough to fulfil the DHA requirements of red porgy larvae for maximum growth. However, a marked positive effect of rotifer DHA content supplementation on larval survival was found. A low larval survival was found when rotifers had a high DPA content, in agreement with the results obtained for other Sparids. This fatty acid was accumulated in red porgy larval tissues in high levels (0.79% dw DPA) when rotifers rich in DPA were the main source of food. Although the external appearance of the juveniles seemed to be normal, X-ray observations showed elevated levels of bone abnormalities associated, in both trials, to low DHA content in the live prey. Among different anomalies, the presence of fused vertebrae was the most frequent deformity for both rearing trials. Although DHA content in the rotifers used for feeding was the only difference a 50% reduction in the number of deformed fish for each type of deformity studied was obtained when the larvae fed higher DHA levels, denoting the important role of this FA in the prevention of deformities at the rotifer feeding stage. Further studies are needed to elucidate the importance of essential fatty acids on the development of bone deformities in fish, since the functions of HUFA are different, and their absolute levels and ratios among them can lead to very different effects in fish metabolism, including bone formation.