저어분 사료 내 여러 동·식물성 단백질원의 혼합 및 첨가가 성어기 넙치(Paralichthys olivaceus)의 소화생리에 미치는 영향

Abstract

The protein requirement in the diet of olive flounder (Paralichthys olivaceus), the main farmed fish species in Korea, is up to over 60%. Protein plays an important role in providing the nutritional value of compound feed ingredients to the cultured fish and is primarily supplied by fishmeal. The demand for fishmeal is increasing due to the continuous development of aquaculture, but the supply is unstable. Therefore, it is necessary to sourced-out protein that can increase fish meal replacement in feed without detrimental effects to the cultured fish. However, most of the studies in olive flounder were conducted at the laboratory level. In this study, growth performance, growth related factors, digestive physiology, and the composition and diversity of gut microbiota were analyzed from olive flounder raised in aquaculture set-up fed diets formulated with decreasing fishmeal content. Four experimental diets were prepared, FM70 [control (CON), 70% fishmeal], FM45 (45% fishmeal), FM35A (35% fishmeal), and FM35B (35% fishmeal + insect meal), and fed to the fish for five months. The sampling period was carried out before the breeding experiment, two months and five months of breeding. Growth performance parameters were calculated after sampling of fish morphological measurements (body weight, total length, etc). Growth hormone and IGF-1 activity were analyzed using an ELISA kit from plasma after blood collection and centrifugation. In addition, IGF-1 mRNA expressed in the liver was analyzed using RT-PCR. The gastrointestinal organs (stomach, intestine, liver) were fixed in 10% formalin and subjected to histological analysis. Digestive enzyme activity was analyzed using ELISA kit, gut microbiota composition was analyzed through total bacterial genomic pyrosequencing and presented at the phylum and genus level, and differences among groups were evaluated through alpha and beta diversity analysis. The results showed that there were no significant differences among experimental groups in growth performance, histological analysis, and gut microbiota diversity. Although there was a significant difference in blood GH activity, there was no significant difference in hepatic IGF-1 mRNA and blood IGF-1 activity in all experimental groups. Trypsin and lipase showed similar activity in all experimental groups, but chymotrypsin was significantly higher in FM45 at 2 months. In addition, FM35B showed significantly low activity at 5 months. Based from the findings of this study, decreasing fish meal content can be utilized in feed formulation for olive flounder reared in typical culture setting without harmful effects on normal biological processes.