In a composite fish culture, catla remains as a ________.

Reason: Catlas serve as surface feeders in a composite fish culture. The practice of growing four to five fish species in a single fish pond is known as composite fish culture. In such systems, these species are selected so that there does not exist any competition for food among them having different types of food habits, e.g. catlas are surface feeders, rohus feed in the middle zone of the pond, mrigals and common carps are bottom feeders, and grass carps feed on the weeds. These species, when together, can use all the food in the pond without competing with one another. This increases the fish yield from the pond.