We know that the body metabolism of animals work efficiently at optimal body temperature. Recently, the changing climatic pattern has left a question mark on the different physiological processes of aquatic organisms in general and cultured aquatic species in particular. Among cultured freshwater species, tilapia Oreochromis niloticus is a global species contributing nearly 8% to the total production in 2016 (FAO 2018). It is cultured in more than 87 countries with an annual growth rate of 3.1% (since 2000) in per capita fish consumption. Here, this study was conducted to evaluate the growth performance, feed utilization patterns and haematological changes of Nile tilapia, Oreochromis niloticus reared at different water temperatures.
A 60 days study using O. niloticus fingerlings was conducted in glass tanks. A total of 80 fingerlings (5.63 cm in length and 2.85 g in weight) were used in this study. Fingerlings were stocked in tanks having 150 litre capacities each at four water temperatures i.e. 28 °C, 30 °C, 32 °C and 34 °C. For each temperature treatment two tanks were used. The stocked fingerlings were fed with commercial floating diet (35% crude protein) twice daily. The faecal matter was collected daily to check the feed utilization efficiency. Water of each experiment unit was changed (50%) once in week. Length and weight of the fingerlings from each treatment was measured scale (nearest to 1 mm) and digital electronic weighing balance (nearest to 1 mg). The organ indices and haematological parameters were measured as per the standard protocols.
The weight gain, weight gain percent, specific growth rate, condition factor and yield were significantly (P<0.05) greater at 34°C than 28 °C, 30 °C and 32 °C. Better condition factor was noticed at 32 °C than other tested water temperature. Improved food conversion ratio was noticed at 34°C followed by 32 °C, 30 °C and 28 °C. However, 30°C is the elite temperature to rear the tilapia which was evidenced from the organ indices. The haematological parameters such as RBC, WBC, MCV and PCV were significantly (P<0.05) higher at 34 °C compared to the other tested temperatures. But, the MCH and MCHC were significantly higher (P<0.05) at 34 °C and 30 °C respectively. This study suggests that increasing water temperature upto 32°C does not significantly affect haematological parameters and growth. However, the feed utilization rate was more at 34 °C as seen from FCR.