과급이에 의해 비만이 유도된 무지개송어(Oncorhynchus mykiss)의 면역생리학적 반응 연구

Abstract

Inappropriate feeding strategies including overfeeding could cause decreasing the feed efficiency, increasing feed wastage and bacterial loads, and obesity, which is induced due to an imbalance between energy consumption and expenditure. Although overfeeding is rather common and thus overfeeding-induced obesity is likely to occur in fish farming industry, most studies have been conducted using fish with high-fat diet-induced obesity. Therefore, the purpose of this study was to understand physiological and immunological changes in rainbow trout with overfeeding-induced obesity. In this study, three independent trials were conducted. In trials 1 and 2, fish were divided into three groups (normal, intermediate and overfed groups) and fed for 8 weeks, and various serum parameters and gene expression were determined to evaluate the effect of overfeeding. In trial 3, fish in the control and overfed groups were sampled at week 4 for transcriptome analysis. In all trials, body mass index (BMI), hepatosomatic index (HSI), and feeding rate were determined at week 0, 2, 4, and/or 8. Five fish from trial 1 were challenged with 2.66 x106CFU/fish of Flavobacterium psychrophilum strain FPRT1 by intraperitoneal (ip) injection and twenty fish exposure to heat stress by increasing water temperature (3˚C/day, final temperature 25˚C) for 10 days. Fish at week 4 and 8 in trial 2 were challenged with 4.06 x 106 CFU/fish and 1.78 x 106 CFU/fish of Aeromonas salmonicida strain 18KR23 by ip injection respectively. Fish at week 4 in trial 3 were challenged with 4.7 x 106 CFU/fish of Aeromonas salmonicida strain 18KR23 by ip injection. Overall, fish in the overfed groups showed significantly higher HSI, BMI, and values in serum parameters such as GOT and GPT. Also, fish in the overfed groups showed higher mortality and infection rate after they were challenged with bacterial pathogens. Granulocyte·macrophage/lymphocyte ratio from fish in the overfed group were significantly lower than those of fish in the control group. From histopathological analysis, fish in the overfed group sampled at week 4 harbor enlarged hepatocytes compared to control fish. From transcriptome analysis, genes involved in energy synthesis, fatty acid metabolism, and PPAR signaling and NOD-like receptor signaling were significantly up-regulated in overfed fish. This study demonstrates that overfeeding for even a short period of time could cause physiological and immunological imbalance in fish, leading them to be more vulnerable to infections. This study provides insights into systemic physiological changes in fish with overfeeding-induced obesity.