Breeding And Larvae Rearing Of The Green Mud Crab, Scylla paramamosain (Estampador 1949) In Captivity
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Date
2015-07
Authors
Islam, Md. Latiful
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Abstract
This pioneer study on the captive broodstock breeding of the mud crab (Scylla paramamosain) consisted with a series of experiments. The larvae rearing trial was fed with Artemia umbrella, enriched rotifer and rotifer from Z1 to Z2 stages followed by Artemia nauplii, enriched Artemia nauplii and commercial diet, respectively from Z3 to megalopa. Highest larval stage index (LSI), significantly higher (p<0.05) megalopa and crablet survival was achieved from enriched rotifer followed by enriched Artemia feeding schemes that had the eicosapentaenoic acid (EPA), docosahexaenoic acid (DHA), n-6 to n-3 and EPA to DHA ratios of 17.32%, 3.82%, 0.20 and 0.22, respectively in megalopa for subsequent metamorphosis to crablet. Growth of mud crab displayed the sigmoid pattern for both sexes with significantly higher (p<0.05) weight gain in males. The female mud crab grew faster (p<0.05) in outdoor tanks, but survival and the proportion of intact crabs were higher (p<0.05) under indoor compartment and outdoor floating boxes. The male crabs attained sexual maturity following spermatogonia, spermatocytes and spermatozoa, whilst, the females completed gonad maturity through proliferation, previtellogenesis, primary vitellogenesis, secondary vitellogenesis and tertiary vitellogenesis. The first sexual maturity appeared at 5 months and 5 to 5.5 months for male and female crabs, respectively, after settlement as crablet. The median maturity age (MA50) was 6.5 months and 6.5 to 7 months for male and females, respectively. Faster maturation in male, asynchrony in intra-sexual and simultaneous intersexual maturation was observed. Mud crab completed the mating with sequential behavior of courtship, pre-mate guarding, moulting, copulation and post copulation guarding. Time spent in each step showed strong-linear relationship (p<0.01) with either male or female body size under 1:1 ratio. Findings on operational sex ratio (OSR), guarding time (GT) and the proportion of intact females under communal mating suggested that the 2: 4 to 2: 8 male-female ratios as superior that had densities of 1.2 to 2/m2, respectively. Reproductive performance and larvae quality seemed similar (p>0.05) among domesticated and natural broodstocks, except higher fecundity and amount of phototaxis larvae in natural broodstock. In case of successive spawning from a single mating event, the 1st and 2nd spawning had higher fecundity and lower dropped eggs. The essential fatty acids of EPA, DHA, total n-3; and total essential amino acid (EAA) were significantly higher (p<0.05) in 1st and 2nd spawned larvae, thus withstand longer time (p<0.05) against starvation than the 3rd spawned larvae. Pragmatically, mud crab broodstock could be developed successfully under captive condition that might support uninterrupted hatchery operation.
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Natural History