• Korean Journal of Ichthyology
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• v.29 no.1
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• pp.75-79
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• 2017

About 10% mortality occurred in cultured rainbow trout Oncorhynchus mykiss at a marine farm in Jeju in 2014. Diseased fish showed markedly abdominal distension and distended stomach. Although parasites, bacteria or viruses were not isolated from diseased fish, numerous Candida sp. were isolated from distended stomach. In experimental infection with Candida sp., mortality was not observed in most fish and clinical sign of distended stomach was not observed in the fish. These results suggest that Candida sp. may not be the etiologic agent of stomach distension syndrome. This is the first report of stomach distension syndrome in seawater farmed rainbow trout in Korea.

• Fisheries and Aquatic Sciences
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• v.3 no.2
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• pp.135-142
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• 2000

In order to clarify the role of gonadal sex steroids in the synthesis of gonadotropin (GTH) subunits in immature rainbow trout, we examined in vitro and in vivo effects of testosterone (T) on the pituitary mRNA levels of GTH I $\beta$, GTH II$\beta$ and a subunits by Northern blot analysis and on the pituitary content levels of GTH I$\beta$ and GTH II$\beta$by radioimmunoassay (RIA). The mRNA levels of the a subunit in T-treated fish were not changed more dramatically than those in control fish both in vivo and in vitro. Interestingly, the mRNA levels of GTH I$\beta$ in T-treated fish were shown to be slightly lower than those in the control fish under these experimental conditions, but no differences were observed in pituitary GTH I$\beta$ contents. In contrast, the mRNA levels and pituitary contents of GTH II$\beta$ subunit were strongly increased by T both in vivo and in vitro. These results demonstrate that the expressions of GTH I$\beta$ and II$\beta$ subunit genes in immatue rainbow trout pituitary are subjected to differential regulation by T.

• Fisheries and Aquatic Sciences
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• v.11 no.3
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• pp.125-132
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• 2008

The development of a fish that functionally provides both antioxidant and fat-reducing effects is an important goal in nutrition and aquaculture research. Dietary conjugated linoleic acid(CLA) can be successfully incorporated in fish muscle and viscera, but CLA and carotenoids have not been evaluated in such fish. An 8 weeks growth trial was conducted using rainbow trout, and all fish were fed twice daily with experimental diets containing graded amounts of CLA(1% and 5%). At the end of the experiment, the daily growth index, feed conversion rate, lipid class, and fatty acid composition were determined. Dietary CLA did not enhance the growth parameters of rainbow trout but did improve the feed conversion rate. The muscular polar lipid content decreased during the feeding period, while the content was stable in the viscera. In addition, a diet high in CLA decreased the polyunsaturated fatty acid content, but had no effect on the content of monounsaturated and saturated fatty acid in muscle.

• Journal of fish pathology
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• v.16 no.2
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• pp.81-90
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• 2003

High mortality with signs similar to viral haemorrhagic septicemia (VHS) such as severe haemorrhages in the skin, muscle and air bladder occurred in the farmed adult rainbow trout, Oncorhynchus mykiss, in Ku-mi and Je-chun area in Korea. The isolates were neutralized by an antiserum against IHNV but not by antisera against VHSV. Electron micrograph of an ultrathin section showed large numbers of bullet-shaped virus particles. The newly isolated rhabdovirus was composed of five structural proteins. In the western blot analysis Ihe anti-DiNV serum strongly reacted with G. N and MI protein. The cumulative mortalities of RTK infected rainbow trout (10-12cm.9-12g) with $10^{3.5}\;and\;10^{1.5}TCID_{50}/m{\ell}$ were 80% and 30%. respectiveIy_ RTJ infected fish showed 50% mortality by infection with $10^{3.5}TCID_{50}/m{\ell}$. Control group and IHNVChAb exhibited no mortality. From these results, the viruses were identified lHNV although diseased fish showed similar sign. with VHS and caused high mortality in large-sized fish.

• Journal of fish pathology
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• v.33 no.1
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• pp.23-34
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• 2020

In recent years, global warming is causing dramatic environmental changes and deterioration, such as hypoxia, leading to reduced survival rate and growth performance of farmed aquatic animals. Hence, understanding systemic immuno-physiological changes in fish under environmental stress might be important to maximize aquaculture production. In this study, we investigated physiological changes in rainbow trout exposed to hypoxic stress by monitoring changes in blood chemistry, leukocyte population, and expression levels of related cytokine genes. Hematological and serological factors were evaluated in blood obtained from rainbow trout sampled at a dissolved level of 4.6 mg O₂ L^-1 and 2.1 mg O₂ L^-1. Blood and head kidney tissue obtained at each sampling time point were used to determine erythrocyte size, leukocyte population, and cytokine gene expression. The level of LDH and GPT in fish under progressive hypoxia were significantly increased in plasma. Likewise, the (Granulocyte + Macrophage)/lymphocyte ratio (%) of fish exposed to hypoxia was significantly lower than that in fish in the control group. Such changes might be due to the rapid movement of lymphocytes in fish exposed to acute hypoxia. In this study, significant up-regulation in expression levels of IL-1β and IL-6 gene appeared to be involved in the redistribution of leukocytes in rainbow trout. This is the first study to demonstrate the involvement of cytokines in leukocyte trafficking in fish exposed to hypoxia. It will help us understand systemic physiological changes and mechanisms involved in teleost under hypoxic stress.

• Korean Journal of Ichthyology
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• v.11 no.2
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• pp.126-133
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• 1999

Ultrastructure of the zona radiata and the micropyle of ripe eggs in the rainbow trout (Oncorhynchus mykiss), catfish (Silurus asotus) and loach (Misgurnus anguillicaudatus) were examined by light, scanning and transmission microscopes. The egg micropyle of rainbow trout and catfish consists of a funnel-shaped vestibule and a tapered canal transversing the zona radiata. The micropyle of rainbow trout and catfish showed the similar structure with flat pit and long canal. The micropylar wall showed the clockwise spiral structure in rainbow trout. The micropyle of the loach showed the type with a hollow pit leading into a short canal and the micropylar wall showed the counterclockwise spiral structure. There are numerous and various size pores at the surface area around the opening in every experimented fish. Interconnecting ridges were observed in the unfertilized eggs of every fish.

• Journal of Aquaculture
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• v.12 no.4
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• pp.293-301
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• 1999

This study was conducted to evaluate the possible utilization of 5 different animal protein sources in juvenile rainbow trout, Oncorhynchus mykiss. Meat and bone meal (MBM), feather meal (FM), squid liver powder (SLP), poultry by-product(PBP) and blood meal (BM) were chosen to be the candidate for the possible ingredients for the dietary fish meal replacer in rainbow trout feed. Six different diets were formulated of isonitrogenous and isocaloric basis of $48\textperthousand$ crude protein and 16.7 kJ/g diet: diet 1, $100\textperthousand$ white fish meal (WFM); diet w, $80\textperthousand$ WFM +20% MBM; diet 3, 80% WFM +20% FM; diet 4, 80% WFM+20% SLP; diet 5, 80% SFM+20% PBP; diet 6, 80% WFM +20% BM. As the dietary protein sources, each diet containing 34.7% of animal protein were supplied by WFM with and without MBM, FM, SLP, PBP or BM and approximately 64.2% of plant protein. After one week of conditioning period, fish averaging 2g were divided into six groups and fed one of the experimental diets for 8 weeks. After eight weeks of feeding trials, there were no significant differences in weight gain and feed conversion ratio among groups of fish fed diet 1, 3, 4, 5 and 6(P>0.05). However, weight gain of fish fed diet 2 were significantly lower than those of fish fed diet 1, 3, 4, 5 and 6(P<0.05). These results indicated that FM, SLP, PBP and BM can be used as a dietary fish meal replacer up to 20% in juvenile rainbow trout.

• IMMUNE NETWORK
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• v.8 no.3
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• pp.67-74
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• 2008

Background: The effects of the dietary administration of two heat-inactivated whole bacteria from the Vibrionaceae family, singly or combined, on innate immune response of the rainbow trout were studied. The two bacteria (Pdp11 and 51M6), which were obtained from the skin of rainbow trout, showed in vitro characteristics that suggested they could be considered as potential fish probiotics. Methods: The fish were fed four different diets: control (non-supplemented), or diets supplemented with heat-inactivated bacteria at $10^8$ cfu/g Pdp11, $10^8$ cfu/g 51M6 or with $0.5{\times}10^8$ cfu/g Pdp11 plus $0.5{\times}10^8$ cfu/g 51M6 for 4 weeks. Six fish were sampled at weeks 1, 2, 3 and 4, and then the main humoral (natural haemolytic complement activity and serum peroxidase content) and cellular innate immune responses (leucocyte peroxidase content, phagocytosis, respiratory burst and cytotoxicity) were evaluated. Results: The serum peroxidase content and the natural haemolytic complement activity increased with time, reaching the highest values in the third and fourth weeks of feeding, respectively. The phagocytic ability of specimens fed the mixture of the two inactivated bacteria was significantly higher than in the controls after 2 and 3 weeks of treatment. The same activity increased significantly in rainbow trout fed the Pdp11 diet for 2 weeks or the 51M6 diet for 3 weeks. Respiratory burst activity was unaffected by all the experimental diets at all times assayed. Cytotoxic activity had significantly increased after 3 weeks in fish fed the 51M6 diet. Conclusion: Our results demonstrated the usefulness of incorporating inactivated probiotic bacteria into fish diets.

• Korean Journal of Ichthyology
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• v.12 no.2
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• pp.111-117
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• 2000

There were observed the histomorphological alterations such as chloride cell hyperplasia, branchial lamellar epithelial separation, the increased cellular turnover of chloride cells, glomerular shrinkage and blood congestion in rainbow trout (Oncorhynchus mykiss) during the seawater adaptation. The ultrastructure by scanning electron microscope (SEM) indicated that the gill secondary lamella of rainbow trout exposed to seawater, were characterized by rough convoluted surfaces during the adaptation. There were observed a large number of mitochondria with the elongate and well-developed cristae in chloride cells exposed to seawater by transmission electron microscope (TEM). The presence of two mitochondria- rich cell types is discussed with regard to their possible role in the hypoosmoregulatory changes which occur during seawater-adaptation. Glomerulus shrinkage and blood congestion were occurred higher in nephrons of seawater-adapted fish than those living in freshwater. Our findings demonstrated that rainbow trout tolerated moderately saline environment and the increased body weight living in seawater was relatively higher than that living in freshwater in spite of histopathological changes.

• Journal of fish pathology
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• v.35 no.2
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• pp.157-165
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• 2022

Single-cycle viruses generated by reverse genetic technology are replication-incompetent viruses due to the elimination of gene(s) essential for viral replication, which provides a way to overcome the safety problem in attenuated viruses. Infectious hematopoietic necrosis virus (IHNV) is a major pathogen causing severe damage in cultured salmonid species. In the present study, we generated a single-cycle IHNV lacking the transmembrane and cytoplasmic domain in the G gene (rIHNV-GΔTM) and evaluated the prophylactic potential of rIHNV-GΔTM in rainbow trout (Oncorhynchus mykiss). To produce rIHNV-GΔTM, IHNV G protein-expressing Epithelioma papulosum cyprini (EPC) cells were established. However, as the efficiency of rIHNV-GΔTM production in EPC cell clones was not high, fish were immunized with a low-tittered single-cycle virus (1.5 × 10² PFU/fish). Despite the low dose, the single-cycle IHNV induced significant protection in rainbow trout against IHNV infection, suggesting high immunogenicity of rIHNV-GΔTM. No significant difference in serum ELISA titers against IHNV between the rIHNV-GΔTM immunized group and the control group suggests that the immunized dose of rIHNV-GΔTM might be too low to induce significant humoral adaptive immune responses in rainbow trout. The involvement of adaptive cellular immunity or innate immunity in the present significantly higher protection by the immunization with rIHNV-GΔTM should be further investigated to know the protection mechanism.