Comparative sensitivity of carp, Cyprinus carpio L. and rainbow trout, Salmo gairdneri Richardson, to Renibacterium salmoninarum

Abstract. The pathogenicity of Renibacterium salmoninarum to carp, Cyprinus carpio L., and rainbow trout, Salmo gairdneri Richardson, was investigated. All carp injected with 4·8 × 10⁸ cells/fish, or 4·8 × 10⁷ cells/fish survived for 38 days. R. salmoninarum was isolated from all moribund fish, but not from the kidney of surviving fish, although R. salmoninarum antigen was detected in several of these fish by the dot blot assay. On the other hand, mortality in rainbow trout was 95% in the fish injected with 4·8 × 10⁸ cells/fish, and 15% in those which received 4·8 × 10⁷ cells/fish. R. salmoninarum antigen was detected by the dot blot assay in all surviving rainbow trout. The number of R. salmoninarum cells was immediately decreased by carp or rainbow trout serum, and the serum bactericidal activity of carp was higher than that of rainbow trout. Carp blood leucocytes had higher phagocytic activity than those of rainbow trout.     

Effect of Oyster Mushroom,Pleurotus ostreatus,Extract on Hemato‐Immunological Parameters of Rainbow Trout,Oncorhynchus mykiss

The current study investigated the effects of oyster mushroom Pleurotus ostreatus, extract on immunological and hematological parameters of rainbow trout, Oncorhynchus mykiss. The fish were fed diets containing 0 (control), 1, and 2% supplementation of the oyster mushroom extract for 6 wk. Blood samples were collected weekly for the first 6 weeks. After 6 wk of feeding, the fish were challenged with Lactococcus garvieae and mortality was recorded. The results of this study showed that feeding rainbow trout an oyster mushroom extract–supplemented diet stimulated phagocytic activity of phagocytic cells, lysozyme activity, and myeloperoxidase activity in serum, but it did not significantly affect the total serum immunoglobulin level. At the same time, a significant increase was found in the number of neutrophils, monocytes, and total white blood cells. Fish fed the diet supplemented with oyster mushroom extract showed reduced mortalities following L. garvieae infection compared with controls. These results show that supplementation of fish diets with oyster mushroom extract at 1 and 2% concentrations significantly imrpoves hematological parameters and modulates the immune response against L. garvieae in rainbow trout.     

Changes of Non-Specific Immune Parameters in Rainbow Trout,Oncorhynchus mykiss,After Exposure to Antimicrobial Agents Used in Aquaculture

Changes of plasma lysozyme and serum bactericidal activity, ceruloplasmin, total plasma protein, serum glucose, hematocrit and leucocrit levels in rainbow trout (Oncorhynchus mykiss) were studied after exposure to formalin and chloramine-T, which are used in aquaculture as anti-ectoparasitic and antibacterial agents. Fish were exposed to formalin at a concentration of 250 ppm for 60 min and exposed to chloramine-T for 5 ppm for 3 h. The parameters were analyzed for rainbow trout exposed to formalin and chloramine-T soon after treatments and rainbow trout exposed to freshwater after 24 h (return) following the treatments. Plasma lysozyme activity decreased after exposure to formalin; however, it was not affected by chloramine-T exposure. Serum bactericidal activity reduced after both formalin and chloramine-T exposure and did not change after returning to freshwater. Ceruloplasmin and total plasma protein were not affected by both treatments. Serum glucose levels of exposed fish elevated and remained at higher levels during recovery period when compared to control values. Hematocrit values of fish exposed to formalin increased; however, no significant change was observed in fish exposed to chloramine-T. Leucocrit levels of fish treated with both formalin and chloramine-T were higher than that of controls.     

In vitro and in vivo effects of rabbit anti-thymocyte serum on circulating leucocytes and production of complement fixing antibodies in thymectomized Oncorhynchus mykiss (Walbaum) infected with Cryptobia salmositica Katz 1951

Rabbit anti-thymocyte serum (RATS) against thymocytes of rainbow trout was toxic to leucocytes from intact and thymectomized rainbow trout at 10 °C under in vitro conditions. The total number of leucocytes decreased significantly in 24 h after RATS was injected intraperitoneally into intact rainbow trout, but the number returned to pre-injection level within 1 week. RATS destroyed a lower percentage of leucocytes in thymectomized fish than in intact fish under both in vitro and in vivo conditions and the recovery in the number of leucocytes was slower in thymectomized fish. The parasitaemia, packed cell volume and production of complement fixing antibody in thymectomized and intact fish (injected with RATS before Cryptobia salmositica infection) were not significantly different from control fish (not injected with RATS), and they both acquired protective immunity against cryptobiosis on recovery. This indicates that RATS is not cytotoxic to B-like cells in the lymphoid tissue which produce complement fixing antibody against C. salmositica and that the protective antigen in C. salmositica seems to be thymus-independent.     

Beneficial effects of thyme (Thymus vulgaris) extract on oxytetracycline‐induced stress response,immunosuppression, oxidative stress and enzymatic changes in rainbow trout (Oncorhynchus mykiss)

The aim of the present study was to investigate the effects of thyme extract (TE) and oxytetracycline (OTC) on rainbow trout (Oncorhynchus mykiss) stress response, immune parameters, oxidative stress and enzymatic changes. The fish were assigned into eight treatments receiving diets with OTC (0 and 2.5 g/kg) and TE (0, 5, 10 and 20 g/kg) for 2 weeks. Thereafter, serum characteristics and gut oxidative status were evaluated. OTC significantly increased serum alanine aminotransferase (ALT) and aspartate aminotransferase (AST) activities, and cortisol and glucose levels; however, TE significantly suppressed these changes. OTC significantly decreased, but TE significantly increased gut catalase (CAT) and glutathione peroxidase (GPx) activities. OTC significantly decreased gut superoxide dismutase (SOD) and increased gut glutathione‐s‐transferase (GST) activities, malondialdehyde (MDA) content and blood monocyte percentage; TE significantly mitigated these changes. TE significantly increased serum total protein, total Ig, lysozyme and ACH50, and blood WBC; however, OTC significantly decreased serum lysozyme and ACH50 activities and blood WBC and neutrophil percentage. In conclusion, OTC administration causes immunosuppression, which might be related to deterioration of fish health. TE augments trout innate immune and antioxidant status and is capable to counteract OTC‐induced health and immune deterioration.     

Experimental validation of geosmin uptake in rainbow trout,Oncorhynchus mykiss (Waldbaum) suggests biotransformation

The bioconcentration of waterborne geosmin in rainbow trout, Oncorhynchus mykiss (Waldbaum) was assessed. Fifty rainbow trout with a mean (SD) weight of 226.6 (29.0) g and lipid content of 6.2 (0.6) % (w/w) were exposed to geosmin in static water for 0, 2, 4, 6, 8, 12, 24, 36, 48 and 120 hr, with one tank containing five fish for each exposure period. Geosmin concentrations were measured in fish tissue and water samples collected over time. With time the geosmin concentration in the fish increased and decreased in the water. However, the total absolute amount of geosmin in the system declined over time which could be explained by induction of biotransformation. This is in accordance with the decreasing lipid normalized geosmin levels in the liver compared with the liver‐free carcass. Geosmin distribution within rainbow trout clearly is not exclusively governed by the lipid content of tissues. In vivo geosmin bioconcentration in rainbow trout is slower and the body burden reached is lower than the generally accepted theoretical model predicts.     

Effects of sulfamerazine on selected haematological and immunological parameters in rainbow trout (Onchorhynchus mykiss, Walbaum, 1792)

In the present study, effects of sulfamerazine on some haematological and immunological parameters of rainbow trout ( Oncorhynchus mykiss ) were examined. Four groups of rainbow trout were fed experimental diets containing either no sulfamerazine (control) or supplemented with sulfamerazine at 100 mg kg⁻¹ (Exp-A), 200 mg kg⁻¹ (Exp-B) or 400 mg kg⁻¹ (Exp-C) for 21 days. Blood samples were taken for the haematological and immunological parameters from fish on the third, seventh, 14th and 21st days of feeding. Haematological parameters [haematocrit, leucocrit, numbers of erythrocytes (RBC) and leucocytes (WBC), haemoglobin (Hb), mean corpuscular volume (MCV), mean haemoglobin concentration (MHC) and mean corpuscular haemoglobin concentration (MCHC)] and immunological parameters [phagocytic ratio (PR) and index (PI), glass-adherent NBT-positive cell activation, total plasma protein and total immunoglobulin (Ig)] were evaluated during the experimental trial. It has been observed that MCV ( P <0.05), PR and PI ( P >0.05) were increased and haematocrit and leucocrit value, numbers of erythrocytes and leucocyte, haemoglobin, MHC and MCHC values and total plasma protein and total Ig levels were decreased in rainbow trout after application of three different doses of sulfamerazine.     

光照颜色对虹鳟行为反应、血浆皮质醇和生化指标的影响

光照是影响鱼类行为、生理以及生长的主要环境因子之一.为研究光照颜色对虹鳟行为反应、血浆皮质醇、生化指标的影响,实验根据鱼类行为学研究方法,分别将白、红、黄、蓝和绿5种光照颜色灯带铺设在室内试验水槽中央底部,将虹鳟放置在水槽同一侧,观察虹鳟在水槽中穿越灯带尾次数及行为反应;根据行为生理学研究方法,分析比较在不同光照颜色下...     

Epidemiology of epizootic haematopoietic necrosis virus (EHNV) infection in farmed rainbow trout, Oncorhynchus mykiss (Walbaum): findings based on virus isolation, antigen capture ELISA and serology

Abstract. The epidemiology of epizootic haematopoietic necrosis virus (EHNV) infection was studied in farmed rainbow trout, Oncorhynchus mykiss (Walbaum). Estimates of mortality during five outbreaks on a commercial farm from 1986 to 1992 ranged from 0033 to 0.2% per day and total mortality did not exceed 3–4% in any outbreak. Affected fish were 0+ and less than 125 mm forklength. Clinical signs were non-specific, and laboratory examination was required to confirm the diagnosis. At the height of the outbreak in 1992, EHNV was demonstrated by virus isolation and antigen capture ELISA in 89% of clinically affected fish and 51% of dead fish, while the prevalence of infection in apparently healthy in-contact fish was 4%. Two and 4 months later the virus was not detected in a group of apparently healthy fish that had been affected earlier. Antibodies specific for EHNV were not found in rainbow trout from the infected farm; however, strong humoral responses were detected by ELISA in two immunized fish, indicating that the virus was immunogenic. These data suggested that EHNV was poorly infective but highly virulent in rainbow trout. Clinical EHNV infection was positively correlated with high rearing density and a low rate of water exchange, and therefore, with presumed poor water quality. Water temperature, which ranged from 11 to 17°C during outbreaks, did not appear to determine the incidence of clinical infection. EHNV infection in farmed rainbow trout was preceded by infection in free-living redfin perch, Perca fluviatilis L., in the water catchment, but it was uncertain whether this represented the source of infection for rainbow trout.     

Alternative matrices for cortisol measurement in fish

Plasma cortisol is the most commonly used indicator of stress in fish but, as the blood sampling procedure itself can be a source of stress, it would be helpful to measure cortisol using less invasive matrices. It is also necessary to find alternative matrices as stress indicators in dead fish in which blood sampling is impossible. In the present study, we investigated transport stress in three aquaculture species, European sea bass (Dicentrarchus labrax L.), common carp (Cyprinus carpio L.) and rainbow trout (Oncorhynchus mykiss Walbaum), by cortisol determination (radioimmunoassay) in plasma and other matrices (skin mucus, gut content, lateral muscle and caudal fin). Cortisol significantly increased after transport in all species and matrices, except in the sea bass gut content, where it remained unchanged. The three species responded to transport stress by producing different cortisol levels. In conclusion, the significant correlation found between plasma cortisol and most of the other matrices opens up the possibility of using them to evaluate stress in fish: mucus sampling is a less invasive method than blood sampling, and in addition to muscle and fin sampling, it can be used in postmortem fish.     

Yersinia ruckeri—A threat not only to rainbow trout

Yersinia ruckeri (Y. ruckeri) can cause mortalities that are contributing to substantial economic losses in the rainbow trout (Oncorhynchus mykiss) aquaculture sector. Because of its most characteristic clinical signs, the disease in rainbow trout caused by this pathogen is called enteric redmouth disease. Although it is considered to affect mainly salmonids, there are reports in the available literature of isolating this bacterium from other fish species, both clinically healthy and diseased. The aim of this study was to analyse the available data concerning yersiniosis in non‐salmonid fish. The analysed data indicate that Y. ruckeri is a threat not only to rainbow trout. Some of the affected species have high commercial importance and mortalities may contribute to high economic losses. The disease symptoms may not be specific and can be different from those characteristic for enteric redmouth in trout, which may lead to misdiagnosis. Collected information indicates that infection with Y. ruckeri should be taken into account in the diagnostic procedures not only in salmonids.     

The Efficacy of a Novel Microbial 6‐Phytase Expressed in Aspergillus oryzae on the Performance and Phosphorus Utilization of Cold‐ and Warm‐Water Fish: Rainbow Trout,Oncorhynchus mykiss,and Nile Tilapia,Oreochromis niloticus

The efficacy and tolerance of a novel microbial 6‐phytase were investigated in rainbow trout, Oncorhynchus mykiss, and Nile tilapia, Oreochromis niloticus. Reference diets were sufficient in available phosphorus (P). The test diet limiting in available P was supplemented with phytase at 500, 1000, or 2000 phytase units/kg feed. The enzyme was effective in increasing total P apparent digestibility coefficient in relation to increasing the dose of phytase in rainbow trout and Nile tilapia. Zinc apparent digestibility improved in relation to phytase supplementation in rainbow trout. P release due to phytase supplementation ranged from 0.06 to 0.18% P/kg feed in rainbow trout and from 0.13 to 0.26% P/kg feed in Nile tilapia. A 58‐d performance trial was conducted to evaluate tolerance of fish to phytase supplementation. Dietary treatments consisted of a basal diet without phytase or supplemented with 2000 and 200,000 phytase units/kg feed. Results indicate that this novel microbial 6‐phytase is well tolerated by fish. Significant improvements for growth as well as feed conversion ratio were observed when the phytase was fed at 2000 phytase units/kg feed. This phytase is proven efficient in releasing P from phytate and could be added when plants are used for fish meal replacement in diets for salmonid and omnivorous fish.     

A comparative tissue distribution study of oxytetracycline in rainbow trout, Oncorhynchus mykiss (Walbaum), and chinook salmon, Oncorhynchus tshawytscha (Walbaum)

Oxytetracycline (OTC), a broad-spectrum antibiotic, is used widely to treat bacterial diseases in farmed fish. In the present study, the time course of OTC concentrations in freshwater rainbow trout, Oncorhynchus mykiss (Walbaum), and seawater chinook salmon, Oncorhynchus tshawytscha (Walbaum), were compared, tissue by tissue, after receiving a bolus dose of the antibiotic (5 mg kg^–1 or 50 mg kg^–1) intra-arterially (i.a.). The OTC concentration–time profiles of rainbow trout tissues were found to be very similar to those of the corresponding tissues in chinook salmon. Therefore, neither water salinity nor fish species seemed to play an important role in the disposition and elimination of OTC in these salmonids. In a separate experiment, rainbow trout were implanted surgically with a urinary cannula and received a single dose of OTC (50 mg kg^–1) i.a. Urine was collected from the cannula daily for 13 days. The amount of OTC excreted into the bile was found to be larger than that eliminated by the urine. These results show the similarity of OTC pharmacokinetics in freshwater rainbow trout and seawater chinook salmon and render support in using a single fish species to study the pharmacokinetics of a drug for other species in the same taxon.     

Evaluation of 100% Fish Meal Substitution with Chicken Concentrate,Protein Poultry By‐Product Blend,and Chicken and Egg Concentrate on Growth and Disease Resistance of Juvenile Rainbow Trout,Oncorhynchus mykiss

The ability of poultry products to replace fish meal in diets for rainbow trout, Oncorhynchus mykiss, depends on their nutrient composition, cost, and consistency. The aim of this study was to assess the ability of three commercially available poultry products (chicken concentrate, CC, poultry by‐product blend, PBB; or chicken and egg concentrate, CE) to maintain growth and disease resistance when substituted for fish meal in a rainbow trout starter diet. A control diet was formulated to contain 48% crude protein and 18% crude lipid; 100% of the fish meal in test diets was replaced with CC, PBB, or CE. At stocking, fry were counted into groups (50 fish/tank) with six replicate tanks for each diet and fed their respective diets four times daily for 8 wk. All the poultry‐based diets supported growth (over 1600% increase over initial weight), nutrient retention, and feed conversion ratios of rainbow trout fry equal to or greater than those observed for fry fed with the fish meal‐based diet. No effect of diet on survival was observed following subcutaneous injection challenge with Flavobacterium psychrophilum. These data suggest that the examined products can be used in place of fish meal for rainbow trout fry without lowering growth and disease resistance.     

Fly Prepupae as a Feedstuff for Rainbow Trout, Oncorhynchus mykiss

Fly larvae may provide an effective method to mitigate two large and growing global concerns: the use of fish meal derived from capture fisheries in aquaculture diets and manure management in livestock and poultry facilities. A 9‐wk feed trial was conducted to determine whether fly larvae could be used as a partial fish meal and fish oil replacement in rainbow trout, Oncorhynchus mykiss, diets. A trout diet was formulated to contain 40% crude protein and 15% fat. Sixty‐seven percent of the protein in the control diet was derived from fish meal, and all the fat was derived from fish oil. Two of the test diets included using the black soldier fly, Hermetia illucens, prepupae, which are 40% protein and 30% fat, as 25 and 50% replacement for the fish meal component of the control diet. The total protein derived from black soldier fly prepupae in these two test diets was 15 and 34%, respectively. A third test diet included using housefly, Musca domestica, pupae, which is 70% protein and 16% fat, as 25% replacement for the fish meal component of the control diet. Data suggest that a rainbow trout diet where black soldier fly prepupae or housefly pupae constitute 15% of the total protein has no adverse effect on the feed conversion ratio of fish over a 9‐wk feeding period. In addition, the diet with black soldier fly prepupae permitted a 38% reduction in fish oil (i.e., from 13 to 8%); however, fish fed black soldier fly diets low in fish oil had reduced levels of omega‐3 fatty acids in their muscle fillets. The findings from this study suggest that either the black soldier fly or the housefly may be a suitable feedstuff for rainbow trout diets.     

Distribution and prevalence of T. bryosalmonae in Austria: A first survey of trout from rivers with a shrinking population

The first evidence of proliferative kidney disease (PKD) in an Austrian river (the River Kamp) was documented in 2016, and no information on the PKD infection status of trout in other rivers was available. Since then, brown trout (Salmo trutta fario) and rainbow trout (Oncorhynchus mykiss) have been collected from rivers in Upper and Lower Austria for different diagnostic purposes. In this study, we summarize the recent findings of a first survey concerning the distribution of Tetracapsuloides bryosalmonae, the causative agent of proliferative kidney disease (PKD), from these samples. Between September 2015 and October 2017, a total of 280 brown trout and 39 rainbow trout were collected from 21 rivers in the provinces of Upper and Lower Austria. T. bryosalmonae was detected by PCR of kidney tissue in 17 of 21 sampled rivers and in 138 of 280 brown trout as well as in 11 of 39 rainbow trout. Pathological signs of PKD (e.g., hypertrophy of the kidney) were observed in 33 analysed brown trout and six rainbow trout samples. No correlations between fish infected by T. bryosalmonae and the parameters size and age class, condition factor, geological origin of the streams and distribution within the river course were found, while positively tested fish are significantly increased at sampling sites exceeding water temperatures of 15°C for median periods of 115 days. The prevalence within the affected streams or stream sections is highly variable, and in single rivers, infection rates of up to 90% are confirmed.     

Quantifying risks of volitional consumption of New Zealand Mudsnails by Steelhead and Rainbow Trout

To assess the risk of transferring alien, invasive New Zealand mudsnails (NZMS) Potamopyrgus antipodarum with shipments of live rainbow or steelhead trout Oncorhynchus mykiss, we conducted laboratory trials to quantify and determine the volitional ingestion of snails from the bottom of laboratory tanks. Approximately, 2000 snails were placed on the bottom of a test tank and groups of 10 fish were added to each tank. After 48 h, the fish were removed, euthanized and the snails in the gastrointestinal tract were counted, and the proportion of snails remaining in each tank was measured. We found that both rainbow trout and steelhead consumed NZMS, but rainbow trout consumed nearly twice the number of snails that were consumed by steelhead trout. Feeding fish a maintenance diet increased the total consumption of snails by fish to an average of 64.5 snails per rainbow trout. Our study suggests that management strategies that depurate fish without feed for 48 h to reduce the risk of transfer of NZMS are not viable in preventing the transport of snails if rearing waters contain snails.     

Triacylglycerol-, wax ester- and sterol ester-hydrolases in midgut of Atlantic salmon (Salmo salar)

Bile salt‐dependent lipase (BSDL) is assumed to be the predominant lipid hydrolase in fish digestive tracts where it hydrolyses dietary triacylglycerols (TAG), sterol esters (SE) and wax esters (WE). BSDL is known to hydrolyse TAG at much faster rates than SE and WE in both fish and mammals. An assay for BSDL has previously been developed for rainbow trout (Oncorhynchus mykiss). However, this setup may not be valid in other fish species. Accordingly, the present study aimed at optimizing previous assays in rainbow trout for use on intestinal luminal contents of Atlantic salmon (Salmo salar L.). Crude intestinal extracts from midgut were desalted before the assay and concentrated bile salts supplemented. In general, the rank order for the degree of hydrolysis in Atlantic salmon was TAG > WE > SE. The optimal assay conditions were determined as being 100 μg protein, 125 μm lipid substrate and 20 mM bile salt (taurocholate) during the 4 h of incubation. Atlantic salmon and rainbow trout of 1500 g showed similar lipolytic activity, while salmon smolts of 300 g showed a significantly lower activity. Furthermore, the inhibition of intestinal lipase activities, especially triacylglycerol hydrolase and sterol ester hydrolase, observed in trout intestinal extracts at bile salt concentrations around 10 mm , was not observed in salmon. This could indicate that the activities in these two salmonids may display different enzyme biochemistry.