Observations on the food and feeding of the Indian mackerel, Rastrelliger canagurta (Cuvier)

The study of the food and feeding of the mackerel,Rastrelliger canagurta was based on the periodical examination of stomach contents of the mackerel and the plankton of the coastal waters near Calicut during the years 1949 and 1950. The relative importance of various food elements have been determined by thenumber and thepoints methods. The mackerel has been observed to feed almost exclusively on plankton organisms. The main food constituents were copepods, cladocerans, larval and adult decapods, peridinians and diatoms. Post-larval bivalves, fish eggs and larvæ, polychæte larvæ, cirripede nauplii, appendicularians and pteropods were minor elements in the food. There was no appreciable difference between the food of the young and that of the adult mackerels. The composition of the food varied from season to season depending upon the fluctuations in the occurrence of various planktonic elements. There was a close correlation between the food constituents and the planktonic organisms of the inshore area. Non-edible forms like salps, medusæ, ctenophores, stomatopod larvæ, chætognaths and noctilucæ were avoided and to that extent there was selective feeding. There was feeding throughout the year although the feeding intensity varied from season to season. There was no marked period of fasting. The feeding intensity was low during the prespawning and spawning periods and comparatively high in the 16 to 20 cm. size group. It was maximum during the period from September to December when edible plankton was abundant