Background: Heat stress is one of the most important environmental stressors challenging poultry production worldwide. Understanding and controlling environmental stressors is crucial for successful poultry production. OBJECTIVES: The aim of the present study was to investigate the effects of melatonin supplementation and darkness regime on reducing the negative effects of heat stress in broiler chickens. METHODS: A total of 400 broiler chickens (Arian) were obtained and subjected to four different groups. The control chickens were grown in normal conditions without receiving any treatment. The positive control birds were grown similar to the control but exposed to an acute heat stress for 6 h/d from days 35 to 40. The dark group chickens were reared under a dark schedule and exposed to heat stress. The birds of the fourth group were reared similar to the positive control but received 40 ppm melatonin in the diet from days 30 to 40 of age. Dead birds were autopsied. The weekly growth performance of chickens was determined and blood samples were taken for hormonal analysis. RESULTS: The number of dead birds due to heat stress was significantly decreased in chickens subjected to the dark program and/or those which received melatonin in the diet compared with those of positive control chickens. Such differences were accompanied with the significantly lower levels of plasma T3, T3/T4 and corticosterone in these groups of chickens. Additionally, plasma thiobarbituric acid reacting substances level was significantly higher in positive control broilers compared to their counterparts. CONCLUSIONS: Our findings indicate a reduction of metabolic rate and heat production in dark regime and melatonin supplementation that can reduce the side effects of heat stress and, therefore, reduce the mortality rate.

Background: The transportation of fish is a common practice in aquaculture. However, the transportation of fish results in significant stress that can cause mortality and disease outbreaks due to compromised immune status. To ameliorate the effect of this stress, it is advocated that a suitable antioxidant be supplemented to fish before subjecting to transportation. Objectives: The present experiment was performed to evaluate the effect of melatonin on haematological parameters and water quality indices of Clarias gariepinus post-transportation.Methods: Forty adult C. gariepinus fishes, weighing an average of 450.46 g and measuring an average of 38.23 cm and 4.46 cm were used for the experiment. They were divided into two groups. Group I (MMF) was supplemented with melatonin in their feed every day for one month while group II (OMF) was not administered melatonin. The subjects were fed a commercial pelleted diet once a day throughout the experiment. They were maintained in a tank made of plastic, and water was originally provided through a flow-through system. Haematological and water quality parameters were determined before and after transportation.Results: After the transportation process, erythrocyte count and packed cell volume of the group I was significantly higher (P<0.05). In comparison to group II, the total leucocyte count, neutrophil count, and neutrophil/lymphocyte ratio of group I were all significantly lower (P<0.05). After transit, group II had considerably higher quantities of nitrite, nitrate, and ammonia (P<0.05) than group I. Following transportation, group II had significantly higher nitrite, nitrate, and ammonia (P<0.05) than group I. However, in group I, dissolved oxygen concentration was greater (P<0.05) than that of group II.Conclusion: Accordingly, it was concluded that melatonin affected various haematological and water quality variables in C. gariepinus and will ameliorate the stress of transportation.