First feeding of winter flounder ( Pseudopleuronectes americanus) larvae: use of Brachionus plicatilis acclimated at low temperature as live prey

Abstract

Brachionus plicatilis are used as live prey for rearing winter flounder larvae at first feeding. This rotifer is grown between 20 and 25 °C (its optimal growth temperature) and then introduced into the 10 °C water in which larvae are reared. The rapid thermal difference between the two media is thought to reduce B. plicatilis quality and consequently affect larval rearing efficiency. In order to optimize larval rearing, a study was conducted to compare the effects of two different diets on larval growth performance and nutritional condition: (1) larvae fed B. plicatilis reared at 24 °C and (2) larvae fed B. plicatilis reared at 24 °C but acclimated overnight at 10 °C. Comparisons were undertaken using morphometric measurements, nucleic acid (RNA/DNA) ratios, total protein content, trypsin activity, and triacylglycerol/sterol ratios. Fatty acid composition of larvae was also studied with a focus on the levels and ratios of three essential fatty acids (docosahexaenoic acid or DHA, eicosapentaenoic acid or EPA, and arachidonic acid or AA). Unique information regarding trypsin activity and lipid components (phospholipid, triacylglycerol, and sterol) of winter flounder larvae is provided in this study. Trypsin activity was detected very early in larvae and was not affected by acclimation of prey. Phospholipid, triacylglycerol, and sterol composition showed no significant difference between the two diets tested and was characterized by high phospholipid content as well as low triacylglycerol and sterol contents. EPA, DHA, AA, DHA/EPA, and DHA/AA decreased from days 12 to 26. Interestingly, DHA content was significantly higher in larvae fed acclimated rotifers and AA content decreased significantly in 26-day-old larvae fed acclimated B. plicatilis. Overall results indicate that overnight acclimation of B. plicatilis at 10 °C is not important for optimizing the rearing of winter flounder larvae although it does influence the fatty acid composition.