암컷 넙치(Paralichthys olivaceus)의 성성숙에 저어분 사료가 미치는 영향

Abstract

The sexual maturity of fish is affected by the environmental  conditions and feed. The main source of protein in fish feed is fishmeal, and the price fluctuation is large due to environmental pollution and overfishing, and the use is gradually changing to a limited extent. Therefore, in this study, the development of gonadal and expression of endocrine hormones in the hypothalamus-pituitary-gonadal axis was confirmed to analyze the sexual maturity of the sub-adult female olive flounder fed a low-fishmeal diet. Fish averaging 26.5 ± 1.45 cm, 165.7 ± 22.65 g (mean ± SEM) were fed three experimental diets; a basal diet without fishmeal replacement was used as a control (CON), 20% of fishmeal replacement from CON (FM20) and 30% of fishmeal replacement from CON (FM30). Water temperature was 18.5 ± 1.01°C while the whole experimental period, 8th, 16th, and 20th weeks, growth performance were measured, and gonad, hypothalamus, pituitary gland, and liver tissue were sampled. The hematoxylin and eosin stains were used for the gonad tissues by the method of organizational analysis. The reverse transcription polymerase chain reaction (RT-PCR) was applied for the hypothalamus, pituitary gland, and liver tissues in the 20 week group to analyze the expression of sexual maturity hormone kisspeptin (Kiss)Ⅰ, gonadotropin releasing hormone (GnRH), preprosomatostatin (PSS)Ⅰ, growth hormone (GH), follicle-stimulating hormone (FSH)-β, luteinizing hormone (LH)-β, estrogen-receptor (ER)α, ERβ and vitellogenin (Vtg). The experimental result showed no difference in weight gain and specific growth rate, condition factor, feed intake, and survival among the experimental groups (P>0.05). Feed conversion ratio, protein efficiency ratio showed the most significantly higher value for the FM30 group (P<0.05). The gonad somatic index (GSI) displayed moderate increases of CON and FM20 in 16 weeks, while the FM30 increased rapidly after 16 weeks. As a result of confirming the female gonadal tissue, the development of oocyte was taking place. The oocyte size measurement result at 8 weeks indicated that the FM30 group had a significantly higher value (P<0.05) than other groups, and there was no significant difference at 16 weeks and 20 weeks. Regarding the sex-mature endocrine hormone analysis, the FM30 group had the lowest values in KissⅠ of the hypothalamus (P<0.05). GnRH is showed no significant difference between the initial and experimental groups (P>0.05). PSSⅠ showed the most significantly higher value for the FM30 group (P<0.05). The pituitary analysis showed no significant difference between the initial and experimental groups in GH (P>0.05). In FSH-β, the FM20 group showed significantly higher values than the initial and all experimental groups (P<0.05). In the LH-β, FM30 group showed significantly lower values ​​than the initial and all experimental groups (P<0.05). As a result of the liver analysis, ERα, ERβ, and Vtg of the FM20 group showed significantly higher values ​​than the initial and all experimental groups (P<0.05). Overall, it concludes that the FM20 group has a positive effect on the sexual maturity of the growing period in olive flounder, and additional studies are needed for each growth stage.