Evaluation of some feeding habits of Rastrelliger kanagurta (Cuvier, 1817) in the Persian Gulf (Hormozgan Province)

The Indian mackerel (Rastrelliger kanagurta) is one of the commercial pelagic fish in the Persian Gulf and Oman Sea. In the current research, food preference index (FP), fullness index (FI), and stomach contents of Rastrelliger kanagurta were evaluated to assess the quantity and type of food which this species consumes in the study area. The samples were collected randomly from Bandar - Abbas and Qeshm Island landing sites. A total of 573 specimens were collected during 2011-2012 of which 299 specimens were female and other 274 specimens were male. The minimum and maximum total lengths were 13.9 and 35.5cm, respectively with the highest frequency in length group of 22-24cm. Results showed that 21.3% of stomachs were full, 44.5% were semi-full and 34.2% were empty. Planktons as well as random food such as bony fish were the main food of this species. Fullness index and Vacuity index for this species were calculated 21.3 and 34.2, respectively. Stomach contents analysis revealed that phytoplankton (66%) and zooplankton (34%) form the main food of Rastrelliger kanagurta. Among the phytoplankton, Bacillariophyceae (86%) was the dominant food followed by Cyanophyceae (8%) and Dynophyceae (6%). Copepods (88%) were dominant zooplanktonic foods. Encrasicholina punctifer was the only bony fish observed. Maximum and minimum of GaSI index were 2.57 (October) and 1.12 (Februrary), correspondingly. Also, condition factor and relative length gut were calculated 1.76 and 2.38, respectively. The results indicated that this fish is a relatively frugal species which consumes plankton as the main food and there is no difference in feeding of male and female.