Mixed-sex tilapia culture model for sub-tropical Nepal.

Abstract Tilapia culture is recent in Nepal, where the subtropical zone allows a 10-month growing period. Water temperatures drop below 20°C for 2 months (mid-December to mid-February) and tilapia does not grow. A tilapia hatchery is required to produce mono-sex fry, but mixed-sex culture can be managed to supply fry for the next culture cycle and excess fry may be a source of fish to provide protein to supplement local feed. On the basis of a series of experiments conducted at the Institute of Agriculture and Animal Science (IAAS), Chitwan, Nepal, a model of a cage-pond integration system for mixed-sex tilapia culture has been developed. This system produces 250-300 g of harvest-size fish from 100-150 g fingerlings stocked in cages with feeding, and about 100-150 g harvest-size fish from stocking 20-30 g fingerlings in ponds without feeding, during one culture cycle of 5 months. Cage culture is for grow-out, whereas pond culture is for producing fingerlings for cage stocking as well as for grow-out. The model has two culture cycles in a year with a net yield of 3.5-4.0 t ha-1 cycle-1. The system produces new recruits for restocking in ponds. Excess recruits are used as feed with the small fish produced in the system supplying about 5% of the feed ingredients. This model yields 7-8 t ha-1 yr-1 in the subtropical climate of Nepal, which is three times higher than the average farmed fish productivity of the country.