Effect of temperature on oocyte development of Oreochromis karongae (Trewavas, 1941)

Oreochromis karongae (Trewavas, 1941) is one of the indigenous Tilapia species exhibiting favourable traits for aquaculture in Malawi. However, commercial fingerling production is still a problem. An experiment was carried out to investigate the effect of raising ambient temperature to 27degreesC on oocyte development of the fish. Female O. karongae were reared under two temperature regimes: at room (20.3+/-0.8degreesC) and at raised (26.5+/-0.5degreesC) temperature for 90 days. Changes in gonadosomatic index (GSI) and oocyte developmental stages were determined every 45 days. Fish samples from the pond (22.5+/-3.4degreesC) from which experimental fish were collected were used for comparison. Results showed that raising temperature to 26.5+/-0.5degreesC significantly enhanced oocyte development. Higher GSIs (Pless than or equal to0.05) were obtained after 45 and 90 days in fish cultured at elevated temperature (0.82+/-0.66 and 1.13+/-0.47%, respectively) than at room temperature (0.06+/-0.03 and 0.37+/-0.05%, respectively). GSI of fish samples from the pond were not different from that of fish from room temperature. After 45 days, relative frequency of mature oocytes was higher (Pless than or equal to0.05) in fish from raised temperature (60.42+/-3.63%) than in fish from room (1.76+/-0.84%) and pond temperature (2.43+/-1.38%). After 90 days, the frequency of mature oocytes in fish from raised temperature was not different from pond fish (8.68+/-2.40 and 10.99+/-3.41%, respectively). Fish from room temperature had a low (Pless than or equal to0.05) frequency of mature oocytes (3.12+/-2.03%). The results suggest that O. karongae has the potential to spawn throughout the year when the temperature is manipulated.