Food and feeding habits of Indian mackerel (Rastrelliger kanagurta) in the southern part of Qeshm Island, Persian Gulf

The study investigated the stomach contents of Indian mackerel (Rastrelliger kanagurta) from the southern part of Qeshm Island in the Persian Gulf from April 2016 through March 2017. The food and feeding behavior of R. kanagurta with a fork length of 17.8 to 22.5 cm was assessed from the analysis of gut contents. The frequency of occurrence and numeric methods were used for stomach content analysis. R. kanagurta fed on diatoms, dinoflagellates, crustaceans, molluscs, forams and ciliates. Organisms of plant origin including diatoms (Bacillariophyceae) and dinoflagellates (Dinophyceae) were the main prey constituting about 72% of food items by number and 66.67% by the occurrence. Coscinodiscus sp. were found to be the most preferable food of plant origin constituting 46.92% by number and 12.88% by occurrence, followed by Guinardia sp. which constituted 9.74% and 7.58% by number and occurrence, respectively. Among zooplankton, crustaceans were the dominant prey contributing to 19.58% of the food items by number and 24.61% by occurrence. Copepoda was the most preferable crustacean constituting 7.57% by occurrence and 5.72% by number. Gastro-Somatic Index (GaSI) was found to be the highest in autumn and the least in winter that is before and after the spawning season. The stomach emptiness index was 36.15% indicating the comparatively gluttonous behavior of the fish. Overall R. kanagurta in the southern part of Qeshm Island in the Persian Gulf is planktonivorous and feeds on a wide range of planktonic organisms.