Effects of size hierarchy on surfacing behaviour and conversion rate in an air-breathing fish Channa striatus

Abstract

Effects of size hierachy on surfacing behaviour and food conversion rate in relation to density and feeding frequency were studied in Channa striatus. In general, crowding increased surfacing frequency in all the weight classes, but affected the food conversion rate of small individuals alone. At any tested density, conversion rate of smaller individual was depressed by the presence of larger individuals; increased feeding frequency did not compensate the negative effects of density. The possible reasons for growth inhibition are: (1) The smaller individuals spend much of their time and energy to escape from the aggressive larger ones than on feeding, and (2) the smaller individuals spend a considerable amount of assimilated food energy on increased surface activity. Unlike density, frequency of feeding improved the conversion rate of both the weight classes and it suggests that the larger individuals could compensate the negative effects of crowding by increased feeding.