The Nile tilapia (O. niloticus) is the most cultivated freshwater species in Panama. To modernize the aquaculture sector, it is necessary to select phenotypes that show the best productive characteristics under stressful situations. It is known that fish, like mammals, exhibit variability in their behavior when faced with stressful agents. When these behavioral differences are related to different physiological responses, the fish might have different coping styles such as proactive or reactive. Therefore, this work aimed to assess whether the behavior is associated with a differential response in variables of performance and animal welfare.
Nile tilapia males with an average weight of 15 grams, previously separated by the proactive and reactive restriction test, were housed in 350 L tanks. The tanks were equipped with a recirculation system and an auxiliary oxygenation system. The Nile tilapia were fed with the same commercial pellet feed.
The physicochemical conditions of the water were monitored daily, and the photoperiod was established at 12:12 (light-dark) hours. The treatments were carried out in duplicate, housing 10 fish of each phenotype in the same tank. Fish were challenged to different hypoxic and temperature conditions on days 35 and 49 of the trial, respectively.
Exposure to different hypoxic conditions consisted of reducing dissolved oxygen levels from 6mg/L to 3mg/L for one hour. At the end of the time, 10 fish from each treatment were individually isolated to evaluate the latency to resume feeding as the time to consume a pellet, and the opercular movements per minute as a physiological evaluation of stress response.
The temperature challenge consisted of increasing the temperature from 28 to 30 °C for one hour, evaluating the same variables described during hypoxia. The final weight and the degree of erosion of the caudal fin were determined.
Proactive fish showed lower latency than reactive fish to resume feeding during hypoxia (p<0.001) and when challenged under increased temperature (p<0.01). Reactive fish showed higher values of opercular movements (p<0.001), and there was no difference in caudal fin erosion between groups (p>0.05). Proactive fish were heavier (p<0.001, Figure 1) than reactive fish at the end of the trial.
These results showed that Nile tilapias separated by their coping styles have differential responses to stressful situations that can affect well-being and productive performance.