The effect of dietary phosphatidylcholine/phosphatidylinositol ratio on malformation in larvae and juvenile gilthead sea bream (Sparus aurata)

Malformation in commercially raised fish, such as cranial, vertebral and gill cover deformities is a major factor reducing their market value. Although these deformities are most apparent in the juvenile and adult stages they may originate from suboptimal nutrition during the critical larval rearing stage. Previous research hypothesized that dietary phosphatidylinostol (PI) was more effective in reducing deformities than the main membrane phospholipid, phosphatidylcholine (PC). Consequently, the aim of this study was to test the effect of different dietary ratios of PC and PI fed to the gilthead sea bream (Sparus aurata) larvae, on developmental performances in juvenile fish in terms of survival, growth and malformation rate. Four microdiet (MD) treatments, that differed in their PC/PI ratio and replaced 75% of the Artemia ration (wt/wt), were fed to 20-34 dph (days post hatching) sea bream larvae. In addition to the high PC/PI or low PI containing MD control, a commercial reference treatment (100% Artemia ration) was also given. At 40 dph, the larvae were graded in all treatments into small (< 1.3 mg dry wt larva^-1) and large (> 2.9 mg dry wt larva^-1) larvae, in order to test if growth rate influenced treatment effect throughout development to 141 dph. There was no marked (P > 0.05) treatment effect on growth rate in 40 dph larvae. On the other hand in later juvenile development (67 dph), decreasing dietary PC/PI ratio contributed to significantly (P < 0.05) better growth and (P > 0.05) higher survival. Moreover, reducing dietary PI markedly (P < 0.05) increased jaw (cranial) deformity in both size groups at 67 dph which may have adversely affected juvenile feeding on a dry hard starter feed. Conversely, increasing dietary PI (reducing PC/PI ratio) showed a non-significant trend of increased skeletal deformity which was markedly (P < 0.05) higher in faster growing larvae in all MD treatments. Although there was no clear effect of PC/PI ratio on gill cover deformity rate, there was a size dependent susceptibility to this deformity where smaller larvae showed the highest incidence of this malformation. Osteocalcin (BGP) mRNA levels correlated well (R² = 0.964) with development in the faster growing fry fed the high PI diet. Higher production of BGP may have reduced (P < 0.05) the jaw deformity while tending to cause over-mineralization and deformity of the skeleton. The results suggest an effective dietary PC/PI ratio of 1.28 for sea bream larvae during culture.