Essential fatty acids for larval mud crab Scylla serrata: implications of lack of the ability to bioconvert C18 unsaturated fatty acids to highly unsaturated fatty acids

Abstract

This study was conducted to examine the effect of essential fatty acids (EFA) on the survival, development and bioconversion of fatty acids in mud crab Scylla serrata larvae. Mud crab larvae held in 1-l plastic beakers (30 ind/l) were fed rotifers that had been enriched with oleic acid (18:1 n−9, OA), linoleic acid (18:2 n−6, LA), linolenic acid (18:3 n−3, LNA), eicosapentaenoic acid (20:5 n−3, EPA) and docosahexaenoic acid (22:6 n−3, DHA) ethyl ester oil during the zoea (Z)1 and Z2 stage. Upon reaching the Z3 stage, rotifers were shifted to unenriched Artemia or Artemia enriched with either EPA or DHA ethyl ester. Further in order to allow comparison of the effect of the enriched rotifers on the fatty acid composition of the Z2 stage larvae, larvae fed enriched rotifers were harvested upon reaching the Z2 stage for fatty acid analysis. The survival of mud crab larvae was more strongly affected by the EFA contained in the Artemia compared to rotifers. Mud crab larvae fed unenriched Artemia showed EFA deficiency signs such as lower survival, longer intermolt period, and a narrower carapace width at the first crab stage, indicating that DHA was superior to that of EPA and followed by LNA and LA. The fatty acid composition of the whole body of Z2 larvae fed rotifers enriched with OA, LA or LNA revealed that the content (g/100 g larvae) of EPA decreased from 1.2 to 0.4–0.8 and DHA decreased from 0.5 to 0.1–0.2, respectively. Moreover, the contents of monoenes increased from 1.4 to 2.5–3.2, indicating dietary EFA deficiency. We conclude that mud crab larvae have a limited or negligible capability to convert C18 unsaturated fatty acids to highly unsaturated fatty acids.