The combined DHA and taurine effect on vision, prey capture and growth in different age larvae of gilthead sea bream (Sparus aurata)

The aim of this study was to determine the short- and long-term effect of rotifer DHA and taurine, individually and through interaction, on larval tissue levels of these nutrients, prey hunting success, growth performance and retinal opsin gene expression, at the end of rotifer and Artemia feeding in developing gilthead sea bream (GSB) (Sparus aurata) larvae. The experiment was designed as a 3 × 3 factorial study in triplicate tanks per treatment. Three levels of rotifer taurine (1.2, 4.9, 10.8 mg g⁻¹ DW) and DHA (5.2, 6.8, 10.1 mg g⁻¹ DW) were tested on 2–14 dph larvae in twenty-seven 400 L V-tanks. All fish were then fed non-taurine enriched Artemia nauplii until 30 dph. There was a significant (P = 0.014) rotifer DHA effect on prey consumption in 13 dph larvae, while rotifer taurine had no marked influence. Rotifer DHA significantly (P = 0.0001) promoted growth (dry weight) alone (P = 0.0001) and through interaction with taurine (P = 0.009) in 31 dph larvae. Moreover, the results implied that rotifer taurine increased assimilation into fish tissue, which resulted in enhanced growth only when prey DHA was below the minimum GSB requirement. Rotifer DHA significantly (P < 0.0001) up-regulated short-wave sensitivity opsin gene expression in 14 dph larvae, while taurine alone had no significant effect. On the other hand, rotifer DHA and taurine individually and through interaction markedly (P < 0.0001, P = 0.022, P < 0.0001, respectively) up-regulated long-wave sensitivity opsin gene expression. However, both prey DHA and taurine did not clearly affect the expression of cone rhodopsin-like 2a and 2b opsin genes. Having said that, rotifer DHA and taurine individually and through interaction significantly (P = 0.034, P = 0.015, P = 0.0005, respectively) affected the gene expression of rod rhodopsin 1. In 31 dph larvae, there was a marked (P < 0.05) rotifer DHA and taurine effect individually and through interaction on the expression of most of the opsin genes analyzed. DHA modulation of the expression of the four cone and rod opsin genes was higher than taurine in younger larvae while taurine appears more dominant over DHA regulating the gene expression of opsin genes in older fish.