Determination of an optimum dietary gamma-aminobutyric acid level and plasma metabolite changes in response to acute temperature stress in juvenile rainbow trout (Oncorhynchus mykiss)

Abstract

Climate change, which is linked to global warming, results in swift environmental alterations, such as rising water temperatures, leading to fatalities, diseases, and epidemics in aquaculture practices. Due to climate change, a study was conducted on rainbow trout (Oncorhynchus mykiss), a significant fish species in aquaculture, to determine the optimal level of GABA supplementation in the diet for growth performance and to investigate physiological responses under temperature stress. Gamma-aminobutyric acid (GABA) used in diet, is an important inhibitory neurotransmitter in the nervous system. It has the ability to reduce stress in humans and animals. The purpose of this research; the current study was conducted to evaluate effects of graded dietary GABA levels on growth performance and stress responses under acute temperature exposure in juvenile rainbow trout. A total of 315 with an average weight between 18.71 ± 0.08 g (mean±SEM) to were randomly divided into 15 groups of , stocked in 15 different glass tanks. For 8 weeks, the 15 tanks represented that were assigned the 5 different GABA (0,50,100,150,200) experimental diets. For the acute stress test, another set of six fish from each tank were exposed to two different temperatures. These 6 fish were distributed in different tanks with water temperatures of 15℃, 20℃, respectively.The fish were exposed to these temperatures for 2 hours followed by a 2 hour recovery period in different tanks filled with water at 15℃. Broken line analysis for weight gain showed that the optimum dietary GABA level could be approximate 140 mg/kg diet in rainbow trout. The results showed that, final body weight (FBW),weight gain (WG), specific growth rate (SGR), protein efficiency ratio (PER) increased significantly (p < 0.05) with GABA level, indicating a dose-dependent relationship. No significant differences were observed Survival (SR), condition factor (CF), hepatosomatic index (HIS), visceral somatic index (VSI) of fish fed all experimental diets (P >0.05). The addition of GABA had no significant effect on crude protein, lipid, and ash content of fish fed all experimental diets (P > 0.05). However, there were significant differences in whole body moisture content; fish fed CON had significantly higher moisture content than fish fed GABA 150 (P < 0.05). Plasma metabolites after of rainbow trout feed the experiment diets 8 weeks, there were no significant differences in glutamic oxaloacetic transaminase (GOT), glutamic pyruvate transaminase (GPT) , total protein (TP), triglyceride (TG) , total cholesterol (TCHO), Glucose (GLU) between fish fed all experimental diets (P > 0.05). A total of 25 amino acids were analyzed and the results showed that GABA supplementation did not lead to any significant change in the different inclusion levels (P > 0.05). A total of 24 whole brain free amino acids were analyzed, and the results showed that GABA supplementation did not lead to any significant change in the different intake levels (P > 0.05). Acute temperature stress, there is no interaction effect of temperature and GABA supplementation levels on the plasma metabolites analysis (P>0.05). Cortisol, GABA 200 at 20℃ showed a significantly higher levels than that of the control diet (P < 0.05). All the remaining diets at the temperatures examined showed increased cortisol levels when compared to the control. Alterations in temperature and the levels of GABA supplementation have been noted to exert a pronounced influence on cortisol and plasma concentrations in fish. Collectively, the present study the addition of dietary GABA supplementation appears to enhance the growth performance of rainbow trout. It is possible that GABA plays a role in influencing the fishes stress response and hormonal regulation. When consider together the study results indicating that GABA supplementation can enhance the growth performance of rainbow trout and that temperature fluctuations may have a significant impact on the levels of GABA supplementation and cortisol levels in fish, these findings provide a meaningful context.