Limiting the use of rotifers
to the first zoeal stage in mud crab (Scylla serrata Forskål) larval
rearing
I.M. Ruscoe, G.R. Williams, C.C. Shelley-2004
Aquaculture, 231(1-4): 517-527
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.
(Darwin Aquaculture Centre, Fisheries Group,
Department of Business, Industry and Resource Development, GPO Box 3000,
Darwin, NT 0801, Australia, e-mail: ian.ruscoe@nt.gov.au)