Growth and body composition of juvenile mud crab, Scylla serrata, fed different dietary protein and lipid levels and protein to energy ratios

Mae R. Catacutan-2002

Aquaculture, 208(1-2): 113-123

Abstract:

The effect of different dietary protein and lipid levels, and protein to energy (P/E) ratios on growth and body composition of the mud crab, Scylla serrata, was evaluated. Six practical test diets were formulated to contain three protein levels (32%, 40% and 48%) at two lipid levels (6% and 12%), each with P/E ratios ranging from 20.5 to 31.1 mg protein/kJ. Individual crabs were stocked in 36 units of 60-l tanks and maintained on a 40% protein diet until each molted (M₀). Newly molted crabs were weighed and fed the test diets until termination at 30 days from the third molt (M₃₊₃₀). Crabs were monitored daily and body weight (BW) taken after each molt, at intermolt and at termination. Average initial BW (11.18±0.66 g) was taken at 18 days after M₀. Carapace width (CW) at M₃₊₃₀ and of the exuviae (at molt 1, 2, and 3 or M₁, M₂ and M₃), weight of exuviae (M₁ to M₃), feed conversion ratio or FCR, duration of intermolt, and total number of days of feeding test diets (M₀ to M₃₊₃₀) were determined. At the end of the study, crabs were freeze-dried for analysis of nutrients in the flesh, exoskeleton and fat body. The FCR (3.21-4.21), intermolt duration and total number of days of feeding test diets (111.3-131.2 days) were not affected by dietary treatments (P>0.05). Analysis of covariance was used with CW at M₁ and BW at M₀₊₁₈ as covariates. CW in the 40% protein with 6% lipid or 40/6 diet (P/E ratio, 27.5 mg protein/kJ) did not increase when lipid was increased to 12% (40/12), and it was significantly wider than crabs fed the 48/6 and 48/12 diets (P/E ratios, 31.1 and 27.2 mg protein/kJ). CW and BW did not differ in the 40% and 32% protein diets and were not affected by dietary lipid level at every level of protein. Ca in the exoskeleton was lowest in the 32/6 diet, while exuviae weight was about one-fourth of BW. Crude fat in the lipid deposit of crabs fed 48% protein diets were low. Results showed that the mud crab, S. serrata, grow well when fed diets containing 32-40% dietary protein with either 6% or 12% lipid at dietary energy ranging from 14.7-17.6 MJ/kg.

(Aquaculture Department, Southeast Asian Development Center, Tigbauan, Iloilo 5021, Philippines, Tel.: +63-33-335-1009; fax: +63-33-335-1008, e-mail: mrc@aqd.seafdec.org.ph)

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