Interactive Effect of Dietary Gamma-Aminobutyric Acid (GABA) and Water Temperature on Growth Performance, Blood Plasma Indices, Heat Shock Proteins and GABAergic Gene Expression in Juvenile Olive Flounder Paralichthys olivaceus

Abstract

Gamma-aminobutyric acid (GABA) is an important inhibitory neurotransmitter in the central nervous system of living organisms and has the ability to reduce the magnitude of stress in humans and animals. In this study, we evaluated the supplemental effects of GABA on normal and high water temperature based on growth, blood plasma composition as well as heat shock proteins and GABA-related gene expression in juvenile olive flounder. For this, a 2 × 2 factorial design of experiment was employed to investigate the dietary effects of GABA at 0 mg/kg of diet (GABA0 diet) and 200 mg/kg of diet (GABA200 diet) in water temperatures of 20 ± 1 °C (normal temperature) and 27 ± 1 °C (high temperature) for 28 days. A total of 180 fish with an average initial weight of 40.1 ± 0.4 g (mean ± SD) were distributed into 12 tanks, of which, each tank contained 15 fish based on the 4 dietary treatment groups in triplicate. At the end of the feeding trial, the results demonstrated that both temperature and GABA had significant effects on the growth performance of the fish. However, fish fed the GABA200 diet had a significantly higher final body weight, weight gain and specific growth rate as well as a significantly lower feed conversion ratio than the fish fed the GABA0 diet at the high water temperature. A significant interactive effect of water temperature and GABA was observed on the growth performance of olive flounder based on the two-way analysis of variance. The plasma GABA levels in fish were increased in a dose-dependent manner at normal or high water temperatures, whereas cortisol and glucose levels were decreased in fish fed GABA-supplemented diets under temperature stress. The GABA-related mRNA expression in the brains of the fish such as GABA type A receptor-associated protein (Gabarap), GABA type B receptor 1 (Gabbr1) and glutamate decarboxylase 1 (Gad1) were not significantly affected by GABA-supplemented diets under normal or temperature stressed conditions. On the other hand, the mRNA expression of heat shock proteins (hsp) in the livers of the fish, such as hsp70 and hsp90, were unchanged in fish fed the GABA diets compared to the control diet at the high water temperature. Collectively, the present study showed that dietary supplementation with GABA could enhance growth performance, and improve the feed utilization, plasma biochemical parameters and heat shock proteins and GABA-related gene expression under the stress of high water temperatures in juvenile olive flounder.

Evaluation of Gamma-Aminobutyric Acid (GABA) as a Functional Feed Ingredient on Growth Performance, Immune Enhancement, and Disease Resistance in Olive Flounder (Paralichthys olivaceus) under High Stocking Density

“…As a result of the analysis of the current study, significantly higher SOD levels were obtained in the experimental groups to which GABA was added. It was found that GABA decreased oxidative stress and increased the activity of antioxidant enzymes in fish, as found in humans, rats, broilers, hens, and pigs, as well as similar to those found in fish and shellfish [15,[20][21][22][23][24][25][26][27][28][29]45]. The results of the present study indicate that dietary GABA can attenuate stress in fish due to high stocking density, which is in agreement with results found in the case of the antioxidant enzyme SOD in Roman hens exposed to heat stress [44], the glutathione (GSH) enzyme in largemouth bass fish exposed to ammonia stress and in turbot fed a high soybean meal diet [52,53].…”

“…Moreover, GABA has been known to possess antidiabetic, antioxidant, and immune-modulating properties [ 35 ]. Due to the well-reported biological activities, GABA as a functional feed additive has been widely used in the animal industry to improve growth performance and to prevent heat stress-related signs in farm animals [ 36 ], fish, and shrimp [ 23 , 24 , 25 , 26 , 27 , 28 , 29 ]. The results of this experiment showed that dietary GABA did not reduce the stocking density stress.…”

“…Although it is a feed additive that has not been largely researched in fish, studies on feed with GABA are also being conducted in aquaculture diets. According to previous research works [ 23 , 24 , 25 , 26 , 27 , 28 , 29 ], GABA has also been proven to have a positive effect on fish and shrimp. In juvenile grass carp, 87.5 mg/kg of GABA in feed had a positive effect on growth and antioxidant ability [ 24 ].…”

“…Olive flounder is one of the most consumed and commercially important marine demersal fish species cultured in East Asian countries like the Republic of Korea, Japan, and China [ 27 , 28 ]. Recently, a series of experiments have been conducted by our group [ 25 , 27 , 28 , 29 ] where we documented that dietary GABA had a beneficial effect on growth performance, feed utilization, hematology, innate immunity, and disease resistance in juvenile olive flounder, Nile tilapia, and whiteleg shrimp. In particular, we have demonstrated that dietary GABA at 200 mg/kg can ameliorate the high-temperature stress in olive flounder [ 28 ].…”

“…Recently, a series of experiments have been conducted by our group [ 25 , 27 , 28 , 29 ] where we documented that dietary GABA had a beneficial effect on growth performance, feed utilization, hematology, innate immunity, and disease resistance in juvenile olive flounder, Nile tilapia, and whiteleg shrimp. In particular, we have demonstrated that dietary GABA at 200 mg/kg can ameliorate the high-temperature stress in olive flounder [ 28 ]. Therefore, in this study, we envisaged to evaluate the growth performance, feed utilization ability, hematological analysis, non-specific immune response, and disease resistance that occurs during normal and high-density culture by adding different concentrations of GABA in feed for olive flounders, Paralichthys olivaceus , as a major domestic fish species in the Republic of Korea.…”