Influence of Different Temperatures and Sexes on the Survival and Stress Responses of Nile Tilapia (Oreochromis niloticus L.)

This study was conducted to assess the influence of different water temperature ranges and sexes on the stress response of Nile tilapia. Sixteen proactive males and sixteen proactive female fish were used in the study. There were eight combinations of factors, and each combination was replicated four times. Changes in eye color pattern (ECP), ventilation rate (VR), and skin color of the fish were monitored after reaching the treatment temperature of the environment. Mortality of fish was also monitored. Results showed that the ECP of fish was significantly (P<0.01) affected by water temperature and sex of fish. Similarly, VR of fish was also significantly (P<0.01) affected by water temperature and sex of fish. Decreased dissolved oxygen (DO) was observed in increasing water temperature which may have also contributed to the stress response of Nile tilapia besides the increasing water temperature. Two out of four fish in T4M died after 6-12 hours of exposure while in T4F three out of four fish died after 2-4 hours. There was a decrease in the final weight of fish in all combinations of factors. On body color, both male and female fish exposed to increasing water temperatures exhibited an intense body color (presence of vertical stripes). From the results of this study, male fish had significantly lower (P<0.01) ECP scores and VR values than female fish when exposed to different ranges of water temperature. Likewise, male fish exposed to high temperatures (39-40°C) survived longer than female fish. Therefore, it can be concluded that male fish are more tolerant to increasing water temperature up to 37°C than female fish since males can easily cope with stress.