Effects of different dietary γ-aminobutyric acid levels on growth, immunity and digestive enzyme activity in juvenile olive flounder, Paralichthys olivaceus

Abstract

치어기 넙치 사료 내 아미노뷰티르산 (Gamma aminobutyric acid, GABA)의 첨가효과를 평가하기 위해 8주간의 사육실험을 실시하였다. 평균 어체중 4.90 ± 0.1g (mean±SD)인 치어기 넙치를 21개의 수조 (40L, 0.153 m2) 에 각 실험구별 30미씩 무작위로 배치하였다 (0.960kg/m2). 실험사료는 GABA가 첨가되지 않은 기초사료 (GABA 92, 기존함량 92mg/kg), 기초사료에 항생제 4g/kg (OTC), 기초사료에 GABA 50 (GAB154), 100 (GAB229), 150 (GAB282), 200 (GAB327), 250 (GAB352) mg/kg 첨가하여 설계하였다. 사육실험 종료 후, 증체율(weight gain)과 일간성장률(specific growth rate)에 있어서 GAB229와 GAB282 실험구가 CON92, GAB154, GAB352, OTC 실험구에 비해 유의적으로 높게 나타났으나(P<0.05). GAB229와 GAB327 실험구간에는 유의적인 차이를 나타내지 않았다(P>0.05). 아밀라아제 소화효소 분석결과, GAB282 와 OTC 실험구가 타 실험구에 비해 유의적으로 높은 활성을 나타냈다(P<0.05). Lysozyme activity에 있어서는 GAB154, GAB229, GAB282 및 GAB327 실험구가 CON92 실험구에 비해 유의적으로 높았으며(P<0.05), Streptocococcus iniae를 접종하여 12일간 공격실험을 진행한 결과, OTC, GAB229, GAB282 실험구의 생존율이 타 실험구에 비해 유의적으로 높게 나타났으나(P<0.05), GAB154, GAB327, GAB352를 실험구간에는 유의적인 차이가 없었다(P>0.05). 따라서, WG을 토대로 한 회귀 분석 (polynomial) 결과 치어기 넙치 사료 내 적정 GABA첨가량은 145mg/kg (GABA 236)이며, GABA 적정 첨가 시 성장, 소화효소, 면역 및 질병 내병성의 효과뿐만 아니라 항생제 대체가 가능할 것으로 판단된다.

An 8-week feeding trial was conducted to determine an optimal dietary level for γ-Aminobutyric acid (GABA) and its effects in juvenile olive flounder, (Paralichthys olivaceus). A total of 630 fish with an average weight of 4.90 ± 0.1 g were stocked by groups of 30 fish into 21, 40 L (0.153 m2) seawater tanks resulting in a 38% coverage area (0.960 kg/m2), and assigned randomly to seven triplicate dietary treatment groups; a basal diet without supplemental GABA as a negative control containing 92 mg kg-1 endogenous GABA (CON92), a positive control composed of CON92 + 4g kg-1 oxytetracycline (OTC), and five other diets prepared by adding 50, 100, 150, 200, and 250 mg kg-1 GABA to the diet resulting in 154 (GAB154), 229 (GAB229), 282 (GAB282), 327 (GAB327) and 352 mg kg-1 (GAB352) respectively (named according to High Performance Liquid Chromatography results). At the end of the trial, results showed that the weight gain (WG) and specific growth rate of fish fed the GAB229 and GAB282 diets were significantly higher (P<0.05) than those of fish fed the CON92, OTC, GAB154, and GAB352 diets. However, there were no significant differences among fish fed the GAB229 and GAB327 diets. Intestinal amylase activity among fish fed the OTC and GAB282 diets had significantly higher enzyme activity than all other GABA supplemented diets. Lysozyme activity among fish fed the GAB154, GAB229, GAB282, and GAB327 diets were significantly higher than those of fish fed the CON92 diet. At the end of the Streptococcus iniae challenge test (day 12) the cumulative percent survival among fish fed the OTC, GAB229, and GAB282 diets were significantly higher than all other diets. However, there were no significant differences among fish fed the OTC, GAB229, and GAB282 diets. There were no significant differences among fish fed the GAB154, GAB327, and GAB352 diets, yet they had significantly higher cumulative survival than the fish fed the CON92 diet. The results of growth, intestinal amylase activity, lysozyme activity, and bacterial challenge indicated that GABA supplementation under the normal stocking density could replace dietary OTC, and improve pathogen resistance as well as growth and intestinal amylase activity in juvenile olive flounder. Based on the quadratic regression (polynomial) analysis of WG, the optimal dietary level could be 236.9 mg kg-1, which results in a supplementation level of 145 mg kg-1.