Rohu - Natural food and feeding habits

Feeding behaviour
During the fry stage rohu is predominantly a planktivorous surface feeder. From the fingerling stage onwards the feeding habit changes and the fish feed in the water column and on the bottom, mainly on filamentous algae, decomposed vegetation, mud and sand (Chondar, 1999). The mouth with its soft fringed lips and sharp cutting edges also indicate that rohu feed on aquatic vegetation. The modified gill rakers suggest that the species is also capable of filter feeding (Chondar, 1999).

Feeding intensity varies with size, the reproductive cycle, season and environment. On average fish in smaller size classes feed more intensively than larger fish and in general, the feeding intensity of juvenile is high throughout the year with a slight drop during the winter months. In adults, the feeding intensity is affected by gonadal recrudescence. Both the males and females feed well when they are immature and there are considerable increase in the feeding intensity as they progress to the maturing stages.  In the mature stages, there is reduction in feeding. After spawning, the spent fishes again start feeding actively. This increase and decrease is more prominent in females than males (Khan and Jhingran, 1975).

Natural food
Rohu fry feed mainly on zooplankton. Juveniles and adults show a strong positive selection for phytoplankton, vegetable debris and aquatic plants and a negative selection for all zooplanktonic organisms (Chondar, 1999). Ontogenic dietary shift of rohu are presented in Table 1. Interestingly, it has been reported by Rahman et al. (2006) that under culture conditions when rohu are fed on formulated feeds they shift their natural food preference from phytoplankton to zooplankton.