Effects of density and different combinations of diets on survival, development, dry weight and chemical composition of larvae of the mud crab, Scylla paramamosain

Studies on the effects of diet on survival, development and growth of larvae of the mud crab Scylla serrata showed that for early larvae (Z1 and Z2), rotifers (Branchionus plicatilis) are a suitable diet although their density significantly affected larval survival and development. All trials showed that larval survival and development steadily increased with density and at 60/mL, the highest survival of 94.7% to Z3 could be reached. However, for the later zoea (Z4 and Z5), feeding with rotifers alone resulted in mass mortality and delayed moult. When fed with Artemia only, newly-hatched larvae suffered from low survival, but for late larvae, it proved to be a good diet. A comparative study of replacing rotifers with Artemia at every zoeal stage showed that larvae initially fed with rotifers but then substituted with Artemia at Z2/Z3 or mixed at Z3 gave best overall zoeal survival. It is noteworthy that in treatments where rotifers were fed at late stages, some Z5 moulted to an extra Z6 stage before metamorphosis. Poor nutritional status during the zoeal stages may have delayed effects on the survival of megalopa. Daily measurement of larval dry weight (DW), carbon (C), nitrogen (N) and hydrogen (H) content showed that at Z2, there were no significant differences between larvae fed with rotifers or Artemia. However, as larvae entered Z3, those fed with Artemia had significant higher DW and C, H, N values. The gaps grew wider as larvae developed further and when fed with rotifers alone, DW and C, H, N of newly moulted megalopa were only 60–70% of those when Artemia was introduced at Z2 or Z3. As C, H, N percentages peaked at late Z5 and the newly moulted megalopa had the highest daily DW and C, H, N increase, a critical period of high nutritional requirements around first metamorphosis was indicated