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

The Indian mackerel (Rastrelliger kanagurta, Cuvier, 1817) is one of the commercial small pelagic fish in the Persian Gulf and Oman Sea. In the current research, feed preference index (FP), fullness index (FI), and stomach contents of Rastrelliger kanagurta were evaluated to assess the quantity and type of feed habits. A total of 573 specimens were collected randomly from Bandar - Abbas and Qeshm Island fishing sites from November 2011 to October 2012. The minimum and maximum total lengths were 13.9 and 35.5cm, respectively with the highest frequency in length group of 24-26cm. Results showed that 21.3% of stomachs were full, 44.5% were semi-full and 34.2% were empty. Planktons and fish were the main and random feed items of this species respectively. 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 feed of Rastrelliger kanagurta. Among the phytoplankton, Bacillariophyceae (86%) was the dominant feed followed by Cyanophyceae (8%) and Dynophyceae (6%). Copepods (88%) were dominant zooplanktonic feed items. Encrasicholina punctifer was the only bony fish observed. Maximum and minimum of GaSI index were estimated 2.57 and 1.12 in October and February, respectively.  Condition factor and relative guts length 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 feed.