Limiting the use of rotifers to the first zoeal stage in mud crab ( Scylla serrata Forskål) larval rearing

Abstract

Commercial mud crab ( Scylla spp.) aquaculture in many countries has been stifled to some degree by a lack of seed stock. A commercially viable larval rearing protocol for Scylla serrata has yet to be established. Two experiments were conducted to assess the requirement for rotifers in the larval feeding regime for S. serrata. These examined the timing of introduction and cessation of rotifers, and co-feeding protocols with Artemia. In the first experiment, it was shown that rotifers were necessary in the feeding regime for acceptable growth and survival, and when used as the only food source during the first zoeal stage (Z1), gave better survival than when co-fed with Artemia. It was also found that when rotifers were removed from the co-feeding regime at Z3, no detrimental effect on growth or survival occurred. Final survival to megalop of 58.67±7.35% was achieved when rotifers were fed singly up to zoea 2 and then co-fed with Artemia through to megalop. Crab larvae fed only Artemia throughout the rearing period took significantly longer to reach the megalop stage and suffered higher levels of mortality. The second experiment investigated the effects on survival, when rotifer feeding was discontinued at Z2, Z3, Z4, Z5 and when rotifers were fed up to the megalop stage (M). Artemia were offered to these treatments from Z2 onwards. A no-rotifer (NR) control that was fed Artemia-only from stocking, was also tested. It was again shown that rotifers, especially in the early stages, promoted acceptable levels of survival and growth. Without rotifers, moulting of crab larvae was delayed and survival was significantly lower during the first two zoeal stages. There was also a significant difference in survival to megalop, and a significant negative relationship between duration of rotifer feeding and survival to megalop. The best survival of 78.00±5.54% was achieved when rotifers were removed from the feeding regime at Z2. The NR treatment had the lowest survival of 32.00±7.51%. These trials established that while rotifers are a valuable inclusion in the feeding regime for larval S. serrata, their use should be limited to the first zoeal stage only to maximise growth and survival.