Transition from endogenous to exogenous feeding in longfin yellowtail Seriola rivoliana larvae under simultaneous effects of daily temperature fluctuation and rotifer Brachionus rotundiformis enrichment.

Temperature and nutrition are suggested as the primary factors affecting larval survival during the transition from endogenous to exogenous feeding in fish. However, little is known about its simultaneous impact during this period. In this study, Seriola rivoliana eggs were subjected to a constant 24 °C (CTE) and a daily temperature fluctuation (DTF) between 22.8 and 25.2 °C until oil droplet exhaustion (5.5 days after hatching). On the other hand, marine fish larvae mostly rely on live feed, with certain nutritional deficiencies such as poor long-chain fatty acids. Thus, rotifer Brachionus rotundiformis enrichment was simultaneously evaluated with temperature using three enrichment diets: Ori-green, S.presso, and a Domestic emulsion. For this purpose, the five experimental groups were established in triplicate using six 100-L tanks with three 10-L containers inside (18 experimental units in total). One hundred eggs were incubated, using a green water system, and 10 rotifers mL^-1 were offered at mouth opening. After oil droplet exhaustion, survival was only affected by temperature (P < 0.01), being higher at DTF compared to CTE. At the same stage, Domestic emulsion resulted in bigger larvae than Ori-green. In a further assay at 3.7 DAH, the relative expression of the trypsin gene was higher at Domestic emulsion compared to S.presso and Ori-green. This study indicates that daily temperature fluctuation can improve larval performance and low levels of EPA and DHA in Domestic emulsion enriched rotifers were not critical for Seriola rivoliana at first feeding.