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Effect of Stocking Density on Survival and Growth of Mud Crablings, Scylla Sp., in Laboratory Conditions

M.Y. Mia
Department of Environmental Science & Resource Management, Mawlana Bhashani Science & Technology University, Santosh, Tangail 1902, Bangladesh

M.J. Alam
Bangladesh Fisheries Research Institute, Brackishwater Station, Paikgacha, Khulna 9280, Bangladesh

Abstract/ Executive Summary:

Mud crablings, Scylla sp. were reared, for a period of six weeks in fiberglass aquarium under laboratory conditions, to determine the effect of four different stocking densities of 1, 2, 3 and 4 crabling/l of water on their survival and growth. Salinity of water was maintained at 25 ppt throughout the rearing period. Stocking rates of 1, 2, and 3 crabling/l resulted in a similar (p>0.05) survival rates of 75, 74i and 83.5%, respectively, that of 4 crabling/l resulted in significantly lower (p<0.05) survival rate of 56%. No significant difference was observed among different stocking densities in average growth of carapace length (CL), carapace width (CW) and body weight (BW).

Keywords: Scylla sp., Stocking density, Survival, Growth

Location: Paikgacha region, Khulna.

Start Date:

End Date:

Program Area: Animal Health and Management

Commodity: Crab

Objectives:

To understand effects of different stocking densities on survival rate and growth of mud crab lings, Scylla species.

Methodology:

The experiment was conducted for a period of six weeks in the Wet Laboratory of Brackish water Station, Bangladesh Fisheries Research Institute. Twelve fibre glass aquariums having 71 cm L x 33 cm W x 30 cm H in size were set in the laboratory with a provision of continuous aeration. Each aquarium was filled up with 25 litre of water having 25 ppt salinity, which was maintained throughout the experiment. Few pieces of small stones and rocks were used in the bottom of each aquarium for the shelter of crablings. The crablings of Scylla sp. (CL, 1.12±0.12; CW, 0.78±0.07 & BW, 0.23±0.07) were collected from natural sources of Paikgacha region, Khulna. They were accustomed to the laboratory conditions for a period of two days prior to release in aquarium. Four different stocking densities of 1, 2, 3 and 4 crablings/litre were tested to examine its effect on survival rate and growth of carblings. Each stocking density was considered as a treatment and assigned in a Randomized Complete Block (RCB) design with three replications. During the experimental period, slaughterhouse waste was given daily as feed to crab lings @ 5% of the biomass. To avoid decomposition of uneaten food particles and as well as to maintain water quality, each aquarium was replenished by new water (nearly 40-50%) regularly through siphoning with a plastic pipe. Temperature of new water was maintained very similar to aquarium water. At least 50% of the stocked crabs in each aquarium were sampled in every week to record data in respect of survival rate, carapace length (CL), carapace width (CW), and body weight (BW). However, the aquariums were checked daily for any mortality of crablings. To measure the CL and CW a vernier slide caliper to the nearest 0.1 mm was used. An electric balance to the nearest of 0.01 g was used for measuring body weight. The experimental data were then analyzed by one way ANOVA and F values were computed. Duncan's New Multiple Range Test (DNMRT) at 1 % level was also employed for further analysis of the results.

Source of Information: Bangladesh J Fish. Res., 10(2), 2006: 159-164

Article Link (Online Journal):

Funding Source:

Total Budget (Tk.) :

Achievement/Findings:

The survival rates of 74- 83.5% with the stocking densities of 1-3 crablings/l suggest that a stocking density up to 3/1 could be practiced in nursing mud crablings under normal laboratory conditions. While stocking density of crablings are very much critical factor for crab culture, it is very important to make sure that same sizes of crab are stocked. Application of sufficient food in time to avoid cannibalism is also very important to notice. To reduce high mortality caused by cannibalism in larval stages, direct stocking of crabs of megalopa and onward stages to the pond maintaining a standard stocking density is recommended.

Knowledge Management: Journal