A multidimensional study on Spotted Sardinella: Biometric, ecological, and heavy metal perspectives from Negombo, Sri Lanka

Biometric parameters, feeding habits, heavy metal content, and fisheries aspects of Amblygaster sirm (Spotted sardinella) in the coastal waters off Negombo, Sri Lanka were studied from August 2022 to March 2023. Length-weight relationships for males, females, and the pooled data were W=0.0029 TL^3.3546, W=0.0035 TL^3.2819 and W=0.0030 TL^3.3459, respectively showing positive allometric growth. Fulton’s condition factors for males, females and pooled data were 0.9047 ± 0.1074, 0.94392 ± 0.08699, and 0.92331 ± 0.09995 respectively. Food mainly consisted of animal parts (77.56%) with crustacean larvae being the most abundant food item (25.51%). The gastro-somatic index showed the highest and lowest feeding intensities in the size classes of 17.5-18.5 cm and 12.5-13.5 cm respectively. Outboard fiberglass reinforced plastic boats and gillnets of mesh sizes 1¼ and 1½ inches are widely used for fishing. The results of the principal component analysis showed that variables such as total length, standard length, head length, body weight, gut length, and gut weight were positively associated with each other. The mean concentrations of Cr, Zn, Cu and Cd in the edible muscles of A. sirm were 10.067 ± 3.658 mg/kg, 7.878 ± 1.856 mg/kg, 5.3857 ± 0.0818 mg/kg and 0.5209 ± 0.0447 mg/kg respectively. These values did not exceed the permissible limits declared by FAO and WHO. Overall, the study found that the fishes were in good physical condition with safe levels of heavy metal content for human consumption.