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Effect of Salinity on the Survival and Growth of Mud Crabling, Scylla Serrata

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

M. M. R. Shah
Bangladesh Fisheries Research Institute, Brackishwater Station, Paikgacha, Khulna

Abstract/ Executive Summary:

An experiment was conducted for a period of eight weeks under laboratory conditions to determine the effect of different salinity levels on the survival and growth of crablings of mud crab, Scylla serrata. The different salinity levels tested were: 5 ppt, 10 ppt, 15 ppt, 20 ppt and 25 ppt. The differences in growth increment in terms of body weight (BW) were significant (p<0.05) among different salinity treatments. The specific growth rate (SGR%/day) values of 2.67, 2.85, 4.07, 4.39 and 4.46 at 5 ppt, 10 ppt, 15 ppt, 20 ppt and 25 ppt, respectively were found significant (p<0.05). The survival rates of crablings were found to be the highest (47.67%) at 25 ppt and lowest (10%) at 5 ppt (p<0.05). The results indicated tha increase of salinity from 5 to 25 ppt had significant effect on the survival and growth of mud crablings.

Keywords: Mud crabling, salinity, specific growth rate, survival rate

Location: Piakgacha, Khulna

Start Date:

End Date:

Program Area: Resource Development and Management

Commodity: Crab

Objectives:

The present study was conducted to evaluate the effect of salinity on the survival and growth of mud crablings of S. serrata.

Methodology:

Salinity tolerance of mud crablings, S. serrata was studied for eight weeks under laboratory conditions at Brackish water Station, Bangladesh Fisheries Research Institute, Piakgacha, Khulna. Crablings were collected from tidal water in the Sankha River of Paikgacha region under Khulna district, Bangladesh. Salinity of the river water was about 15 ppt and collected crablings were temporarily kept in same salinity for a day. Different test saline waters (5, 10, 15, 20 and 25 ppt) were prepared by mixing brine with tap water. The tap water was stored in plastic containers and aerated continuously at ambient room temperature (30°C). All salinity were checked with a hand held refractometer to the nearest 1 ppt. In total 15 fiber glass aquaria (50 L) were used for this experiment. Each aquarium was filled up with 30 liter saline water and few pieces of gravel and stone for shelter of test specimens. Ten crablings (carapace length: 1.43±0.21 cm; carapace width: 2.06±0.29 cm and body weight: 1.67±0.75 g) were released into each of five aquarium with five different salinity treatments viz., T₁ (5 ppt), T₂ (10 ppt), T₃ (15 ppt), T₄ (20 ppt) and T₅(25 ppt) and the experiment was replicated thrice. The crablings were fed daily with slaughterhouse waste @ 5% of the total biomass. Tested saline water in each aquarium was replenished (app. 60-80%) daily with new supplies of saline water. At the time of replenishment, observations and counts were done for survival of crablings. Growth performance in respect of body weight (BW) of crablings was recorded at weekly interval. Growth gained by the crablings was expressed in Specific Growth Rate (SGR) by the following formula: Specific Growth Rate (SGR%/day) = (logeL2 – logeL1) x 100/ (T₂ – T₁); where, L₂ = Final weight of crabling (g), L₁ = Initial weight of crabling (g), T₂ – T₁ = Duration of the experiment (day).

Source of Information: Univ. j. zool. Rajshahi. Univ. Vol. 29, 2010 pp. 29-32

Article Link (Online Journal):

Funding Source:

Total Budget (Tk.) :

Achievement/Findings:

Hence, it could be concluded that mud crab is a euryhaline species but specific saline water is essential for its larval metamorphosis and breeding. Since the salinity of estuary and sea water is not fixed but related with some factors like temperature, current, turbidity etc, so further research is needed using more higher saline water above 25 ppt to at least 45 ppt. In the present study, survival rate is lower than other result though. In the present study, cannibalism occurred within the crablings as newly moulted crablings came within the reach of other crabs. This happened due to the experiments being carried in a closed water body like fiber glass aquarium. This might be one of the factors affecting the lower survival of mud crablings in this study.

Knowledge Management: Journal