Eco-Biology and Biochemical Composition of Lates Calcarifer (Bloch, 1790) In Coastal Water of Bangladesh

Abstract

The present study was conducted for a period of two years from July 2013 to June 2015 to assess the ecology, food and feeding habits, body composition and fishery of Lates calcarifer in Khulna district of Bangladesh. Among the water quality and hydrological parameters, air and water temperature, water transparency, salinity, rainfall, pH, dissolved oxygen and free carbon dioxide were recorded on monthly basis in different types of habitats including coastal rivers and ghers (polder area). For the analysis of food and feeding habits of the studied fish, a total of 300 specimens including 180 adults and 120 juvenile were dissected and studied under the microscope. Monthly variation in the degree of feeding was also studied. In case of juvenile L. calcarifer maximum 26.67% stomachs were found as ½ full followed by full (25%), ¾ full (17.50%), 1/3 full (15%), ¼ full (8.33%), empty (4.17%) and 1/8 full (3.33%) stomachs. Whereas for adults, maximum 28.89% stomachs were found as full followed by ¾ full (22.78%), ½ full (20%), empty (11.67%), 1/3 full (9.44%), ¼ full (5%) and 1/8 full (2.22%) stomachs. Following categories of food items were recorded from gut analysis of both juvenile and adult specimens: algae or phytoplankton, zooplankton (protozoans and small crustaceans), large crustaceans, insects, teleosts and unidentified food materials. For the analysis of body composition moisture, protein, fat, ash and minerals (phosphorus, iron, calcium and magnesium) were measured in both male and female at different phases, i.e. juvenile, adult and spent. In male, the highest moisture was found in spent (71.230±0.843%) and the lowest amount was found in adult fish (69.633±0.464%). In female the highest moisture was recorded in spent (72.453±0.552%) and the lowest moisture was found (70.190±0.877%) in adults. For protein, the highest amount was found in male adult (22.940±0.255%) and the lowest amount was found in female spent fish (16.207±0.342%). In case of fat, the highest amount of fat was found in adult male (6.017±0.235%) whereas, the lowest amount was found in female spent fish (3.117±0.440%). This study revealed the variation in body composition that helps stakeholders to manage the species appropriately. Information regarding the fishery of L. calcarifer has been collected by visiting various fishing and landing centres of southern region of Bangladesh. Three visits were made in each month and necessary data were recorded. A range of fishing gears and methods including nets (veshal jal, khepla jal, ber jal and punti jal) and katha fishing were recorded. Restriction should be made against the use of harmful fishing gears and methods used in capturing studied species. Status of fish landing, marketing channel, profit analysis were also studied in this study. The present study showed the ecology, food and feeding habits, biochemical compositions and fishery of L. calcarifer, these findings would be helpful for the future researchers who will conduct further research on this fish species.