Effects of environmental temperature on the growth performance of a tropical Oreochromis esculentus (Graham, 1928). Implications for the species conservation

Climate variability and change are currently recognised global challenges. However, the impacts of rising temperatures may be greatest on tropical freshwater fish, which already exist in warm environments and may be living close to their critical thermal maximum. However, there is limited species-specific information on tropical species' adaptive capacity to increased temperature. This study examined various growth attributes in juvenile populations (farmed, L. Kacheera and L. Nabisojjo) of a critically endangered tropical Oreochromis esculentus to determine its adaptive potential. Fish were acclimated at 25, 28, 31 and 34 degrees C for 28 days. Overall, survival rates were high. Growth coefficient b was not significantly different from three (b = 3) in all treatments, implying isometric growth. The specific growth rates (SGRs), body condition K, and hepato-somatic indices (his) declined as the acclimation temperatures increased. Although SGR showed significant variations only among populations, the highest in L. Nabisojjo, K and HSI showed significant variations among treatments. Overall, the growth attributes declined at higher acclimation temperatures, but remained within acceptable ranges, implying that the species may attain normal growth at elevated temperatures experienced in outdoor aquaculture systems, despite its warm environmental background. Hence, we recommend selective breeding for temperature resilience and species introduction into aquaculture using broodstock from L. Nabisojjo.