Feeding ecology of the freshwater fish rohu Labeo rohita(Hamilton 1822): a case of intelligent feeding in the periphyton-based environment

Feeding preferences of rohu Labeo rohita(Ham) were studied in two environments (an open area without substrate; a closed area with bamboo substrate) in a traditional fish pond. Diet breadth indices of Levins, Smith and DB (χ2) were compared for three resources (plankton from the open area; plankton and periphyton from the closed area). The fish exhibited a greater diet breadth in the closed area. Initially it preferred plankton, but later it shifted to both food resources. Food selectivity studies using DB (χ2) against the ratio of the observed gut content mean to the resource mean suggest that rohu utilizes both plankton and periphyton from the closed area efficiently. The feeding rate of rohu, which is a water column feeder without any specialized mouth adaptation for grazing on periphyton, might have increased due to the existence of the plankton-periphyton interface zone in proximity to substrate in the substrate-based area. The fish intelligently shifted its food niche from plankton to the plankton-periphyton interface zone accelerating ingestion of planktonic food.