Dietary taurine improves vision in different age gilthead sea bream (Sparus aurata) larvae potentially contributing to increased prey hunting success and growth

The effect of different levels of dietary taurine on vision, prey hunting success and growth was tested in developing larval gilthead sea bream (GSB; Sparus aurata). Fifteen 17 L aquaria were stocked with 3000 fertilized eggs aquarium⁻¹ from a local GSB broodstock, which allowed the testing of 5 prey taurine treatments in triplicate aquaria treatment⁻¹. Nine aquaria tested the effect of the non-taurine enriched rotifer (Brachionus rotundiformis) control (1.7 mg g⁻¹ DW) and two taurine enriched rotifer treatments (6.6 and 11.0 mg g⁻¹ DW) in 2 to 13 dph larvae followed by feeding non-taurine enriched Artemia nauplii (36.6 mg g⁻¹ DW) to all treatments from 14 to 31 dph. Larvae in another 6 aquaria were fed control rotifers (1.7 mg g⁻¹ DW) from 2 to 13 dph followed by testing the effect of taurine enriched Artemia nauplii (51.5 and 61.9 mg g⁻¹ DW) on 16 to 31 dph larvae. In parallel, GSB fertilized eggs from the same broodstock were stocked (100 eggs L⁻¹) in fifteen 400 L conical, polypropylene tanks, which tested the 5 rotifer and Artemia taurine levels in triplicate tanks treatment⁻¹. Only rotifer consumption (mastax number) in 7 and 13 dph larvae and dry weight of 31 dph larvae were determined in the aquaria, while total length, essential fatty acid profile, taurine level, opsin abundance and gene expression of selected opsin genes in different age larvae were determined from the much larger biomass of the 400 L tanks. The growth of 3 and 13 dph larvae were significantly (P < 0.05) correlated with rotifer and larval body taurine levels in a dose-dependent manner. Moreover, rotifer ingestion (mastax number) significantly (P < 0.05) improved in 13 dph larvae with rotifer taurine level. The growth promoting effect of rotifer taurine continued to significantly (P < 0.05) influence larval length in older 21and 26 dph larvae, although this effect diminished (P > 0.05) in 31dph larvae. The contribution of taurine to improved vision was supported in 31 dph larvae, which exhibited significantly (P < 0.05) increasing retinal opsin protein abundance with rotifer taurine level in a dose dependent manner. In fact, dietary taurine markedly (P < 0.05) improved the gene expression of 5 different opsins in 8 and 31 dph larvae. Nevertheless, the correlation between rotifer taurine and larval fatty acid content suggests that the taurine-modulated production of bile salts facilitated lipid digestion and absorption, which also might have promoted growth.