Resistance Of Rainbow Trout Research Articles

Acquired resistance in rainbow trout against Gyrodactylus derjavini

AbstractInvestigations were conducted on the host response in rainbow trout and the associated changes in mucous cell density during infection with the skin monogenean Gyrodactylus derjavini. Parasite populations increased on all naive hosts and peaked 4–5 weeks p.i. after which infection levels decreased. Introduction of naive fish into responding host populations resulted in heavy infections of the naive fish, whereas parasite expulsion continued in the responding host groups showing an acquired, non-sterile immunity. This non-sterile immunity lasted at least a month as these hosts were refractory to reinfection despite being exposed to a high infection pressure. Mucous cell hyperplasia was seen in some groups during the intermediary phase of infection, but at the termination of the study a significant depletion was evident. Passive immunization of naive host (with sera from immune hosts) did not confer protection. This indicates differences between host responses to G. derjavini compared to responses against other pathogens where such a passive immunity has been described.

Plasma proteins of rainbow trout (Oncorhynchus mykiss) isolated by binding to lipopolysaccharide from Aeromonas salmonicida

In an attempt to find plasma proteins that might be involved in the constitutive resistance of rainbow trout to furunculosis, a disease caused by Aeromonas salmonicida (AS), we purified serum and plasma proteins based on their calcium- and carbohydrate-dependent affinity for A. salmonicida lipopolysaccharide (LPS) coupled to an epoxy-activated synthetic matrix (Toyopearl AF Epoxy 650M). A multimeric family of high molecular weight (96 to 200-kDa) LPS-binding proteins exhibiting both calcium and mannose dependent binding was isolated. Upon reduction the multimers collapsed to subunits of approximately 16-kDa as estimated by 1D-PAGE and exhibited pI values of 5.30 and 5.75 as estimated from 2D-PAGE. Their N-terminal sequences were related to rainbow trout ladderlectin (RT-LL), a Sepharose-binding protein. Polyclonal antibodies to the LPS-purified 16-kDa subunits recognized both the reduced 16-kDa subunits and the non-reduced multimeric forms. A calcium- and N-acetylglucosamine (GlcNAc)-dependent LPS-binding multimeric protein (∼207-kDa) composed of 34.5-kDa subunits was purified and found to be identical to trout serum amyloid P (SAP) by N-terminal sequence (DLQDLSGKVFV). A protein of 24-kDa, in reduced and non-reduced conditions, was isolated and had N-terminal sequence identity with a known C-reactive protein (CRP) homologue, C-polysaccharide-binding protein 2 (TCBP2) of rainbow trout. A novel calcium-dependent LPS-binding protein was purified and termed rainbow trout lectin 37 (RT-L37). This protein, composed of dimers, tetramers and pentamers of 37 kDa subunits (pI 5.50–6.10) with N-terminal sequence (IQE(D/N)GHAEAPGATTVLNEILR) showed no close homology to proteins known or predicted from cDNA sequences. These findings demonstrate that rainbow trout have several blood proteins with lectin properties for the LPS of A. salmonicida; the biological functions of these proteins in resistance to furunculosis are still unknown.

Induced resistance in rainbow trout, Oncorhynchus mykiss (Walbaum), to gill disease associated with the microsporidian gill parasite Loma salmonae.

Branchial xenomas were detected by week 5 and disappeared by week 10 after naive juvenile rainbow trout, held at 14.5 °C, were fed or intubated with Loma salmonae-infected gill tissue preparations. Upon re-challenge with L. salmonae, these fish were protected from disease and branchial xenomas did not develop. Branchial xenomas were never detected in naive fish held at 10 °C and exposed to L. salmonae. When these fish were re-challenged with L. salmonae at 14.5 °C, they were also protected from the disease. Branchial xenomas also developed after naive fish, held at 14.5 °C, were injected intraperitoneally with a semipurified preparation of fresh spores, but generally did not develop after intraperitoneal injection with a preparation of spores subjected to freezing and thawing before use. Fish that had received fresh spores intraperitoneally were completely resistant to disease when re-challenged via oral delivery of spores, whereas those that had received frozen spores were incompletely, but significantly, protected from disease compared with naive fish. We conclude that infection with L. salmonae induces strong protection towards the disease upon re-exposure to spores, and that the protection does not depend on the completion of the parasite's life cycle, thus establishing the basis for further research on vaccine development for this disease.

Influence of combined vitamins C and E on non-specific immunity and disease resistance of rainbow trout, Oncorhynchus mykiss (Walbaum).

The effect of various combinations of vitamins C and E on immune response and disease resistance was investigated in rainbow trout, Oncorhynchus mykiss (Walbaum). The following combinations of vitamins were included in the diet (C/E): 0/0, 0/800, 2000/0, 30/30, 30/800, 2000/30, 2000/800. Liver ascorbic acid and alpha-tocopherol contents reflected the dietary treatments well. Complement levels showed no significant differences. The combination of the high dietary doses of vitamins C and E significantly stimulated lymphoproliferation induced by Concanavalin A when compared with fish fed a low level of both vitamins, but also when compared with fish fed a low level of vitamin C and a high level of vitamin E. The highest macrophage oxidative burst activity, measured by chemiluminescence, was found in fish receiving both vitamins at high levels. In the disease resistance experiments, the best survival rates in trout infected with viral haemorrhagic septicaemia virus were achieved with diets containing both vitamins at a high level, or at least one at a high and the other at a low level. Highest mortalities in fish infected with Yersinia ruckeri occurred in trout fed double-deficient or double low diets. The best survival of fish exposed to Ichthyophthirius multifiliis was achieved with diets high in one and low in the other, or high in both vitamins. However, differences were not statistically significant in the parasite experiment.

Comparative metabolism of 2-acetylaminofluorene by rainbow trout and rat liver subcellular fractions

In order to assess the cause of the resistance of rainbow trout ( Oncorhynchus mykiss), Shasta strain, to the hepatocarcinogenic effects of 2-acetylaminofluorene (AAF), we have investigated the metabolism of this model chemical by subcellular fractions from trout liver. Treatment of trout with 3-methylcholanthrene (3-MC) enhanced the rate of metabolism of AAF by liver microsomes. The major AAF metabolites produced by trout liver microsomes at saturating substrate concentration (34.3 and 19.5 μM AAF for control and 3-MC-induced microsomes, respectively) were 7-hydroxy-AAF and 5-hydroxy-AAF which represented 75 and 21% of total AAF metabolites, respectively for control microsomes, and 79 and 18% of total metabolites, respectively for induced microsomes. With both control and 3-MC-induced microsomes, N-hydroxy-AAF (the proximate carcinogen of AAF) was a minor metabolite accounting for less than 1% of total AAF metabolites. At a low substrate concentration (0.18 μM AAF), 7-hydroxy-AAF formation accounted for 95 and 91% of total metabolites for control and 3-MC induced microsomes, respectively, and a slight relative increase in N-hydroxy-AAF production (1.5–2.5%) was observed. Liver microsomes from untreated male Sprague-Dawley rats (a species susceptible to hepatocarcinogenesis by AAF) formed N-hydroxy-AAF in greater proportions (14-fold) and ring-hydroxylated metabolites in smaller proportions compared to trout liver microsomes. The activities of cytosolic N-hydroxy-AAF sulfotransferase and acyltransferase in trout liver (24 and 17 pmol/mg h −1, respectively) were found to be substantially lower than those reported for Sprague-Dawley rats. The low activity of hepatic enzymes implicated in the metabolic activation of AAF (AAF-N-hydroxylase, N-hydroxy-AAF-sulfotransferase, and N-hydroxy-AAF acyltransferase) coupled with a relatively high capacity of the trout liver for ring-hydroxylation (detoxification) of AAF may explain, in part, the resistance of rainbow trout to the hepatocarcinogenic action of AAF.

Spontaneous bactericidal and complement activities in serum of rainbow trout ( Oncorhynchus mykiss) genetically selected for resistance or susceptibility to furunculosis

Half-sib families of rainbow trout ( Oncorhynchus mykiss) selected for heritable susceptibility or resistance to furunculosis and belonging to 3 successive generations were reared in a fish farm and blood samples were periodically collected. Pooled and individual sera were screened for the effectiveness of two kinds of activity generally assigned to the alternative complement pathway: bactericidal activity was assessed against suspensions of an avirulent form of Aeromonas salmonicidaand spontaneous haemolytic activity (SH 50) was titrated using rabbit erythrocytes in the presence of EGTA and Mg 2+. Significant differences in serum bactericidal properties generally occurred between susceptible and resistant families of trout, although transient variations could occur. Seasonal fluctuations, irrespective of the age of the fish, were also observed. However, whereas correlation between the bactericidal activity or alternative complement pathway and the fish resistance could be observed, it was more difficult to demonstrate between the bactericidal activity and the alternative complement pathway. It is concluded that the alternative complement activity, although significant in natural defences, accounts only partly for furunculosis resistance and that bactericidal activity of serum is a more reliable marker of this resistance in rainbow trout.

Metabolism of 2-acetylaminofluorene by rainbow trout

In order to examine factors that may contribute to the reported resistance of rainbow trout, Shasta strain, to the well-known hepatocarcinogenic effects of 2-acetylaminofluorene (AAF), the in-vitro and in-vivo metabolism of [ 14C]AAF in trout has been examined. Trout (compared to rat) liver microsomes metabolized AAF more efficiently, producing 3-fold larger amounts of ring-hydroxylated metabolites (7-hydroxy-AAF and 5-hydroxy-AAF), but 5-fold less N-hydroxy-AAF. Freshly isolated trout hepatocytes extensively metabolized AAF to form the same ring-hydroxylated metabolites and their respective glucuronide and sulfate conjugates. N-OH-AAF (plus its conjugates) and covalently-bound AAF derivatives amounted, respectively, to < 1% and 1.4–1.6% of total metabolites. Liver DNA of trout treated with AAF contained a single AAF-DNA adduct identified as N-(deoxyguanosin-8-yl)-2-aminofluorene (the major persistent AAF-DNA adduct found in rat liver). The level of this adduct (12 attomoles/μg DNA) was about 1000-fold lower than the level of AAF-DNA adduct previously reported in rat liver. The data show that trout liver, compared to rat liver, is considerably less efficient in metabolizing AAF to carcinogenic metabolites, and more efficient in forming nontoxic products, thus possibly explaining, in part, the resistance of trout to AAF-induced hepatocarcinogenesis.

Enhancement of resistance to bacterial infection in rainbow trout, Oncorhynchus mykiss (Walbaum), by oral administration of bovine lactoferrin

Abstract Bovine lactoferrin was evaluated for its ability to enhance resistance of rainbow trout, Oncorhynchus mykiss (Walbaum), to infection with Vibrio anguillarum. Oral administration of lactoferrin (100 mg kg−1) to fish daily for 3 days prior to an intraperitoneal challenge with V. anguillarum resulted in increased survival rates, and enhanced resistance against Streptococcus sp., although to a lesser extent. In lactoferrin‐treated fish, an increase in phagocytic and chemiluminescent (CL) activities of pronephros cells against V. anguillarum was observed. The phagocytic and CL activities of cells against Streptococcus sp. were also significantly increased. However, no in vitro bactericidal activities of lactoferrin against V. anguillarum or Streptococcus sp. were observed. This suggests that the lactoferrin enhanced the resistance of the rainbow trout against bacterial infection through the activation of phagocytes.

ペプチドグリカンの長期経口投与がニジマス稚魚の抗病性と成長に及ぼす影響

Juvenile rainbow trout, weighing 0.12g on average, were fed on diets containing 0.2 and 2mg/kg of peptidoglycan (PG) derived from bifidobacterium thermophilum at a ratio of 3% body weight (BW) for 56 days, so that fish were given 6μg or 60μg PG/kg BW per day. On days 28 and 56, fish were challenged by immersing them in Vibrio anguillarum suspension, and the mortality was monitored for 21 days. PG did not influence the growth of fish at these doses. On day 28, PG-administrated groups showed a significantly higher survival rate compared with the control group. On day 56, however, no significant difference in the survival rates was observed between the PG-administrated group and the control group at either dose. These results indicate that the oral administration of PG enhances the resistance of rainbow trout against V. anguillarum infection, and a longer administration of more than 28 days may lead to a decrease in disease resistance.

Disease resistance in rainbow trout ( Oncorhynchus mykiss) selected for stress response

Two lines of rainbow trout, selected for either high or low stress response as measured by blood cortisol levels, were challenged by two bacterial pathogens, Aeromonas salmonicida, causing furunculosis and Vibrio anguillarum, causing vibriosis. In both challenge experiments, the survival rates during the experiment, and the total accumulated mortality at termination of the experiment, were significantly different between the two lines. Whereas in the furunculosis challenge the death rate in the high-stress response line was higher than in the low-stress response line, the opposite was true for the vibriosis challenge. Two non-specific immune components were analysed in the challenged fish: serum haemolytic activity, which was higher in low-stress fish than in high-stress fish; and lysozyme, which had higher measures in high-stress fish. The results of the present study indicate that selection for stress response affects the disease resistance of rainbow trout, albeit not in an unambiguous direction in respect to different diseases.

Paternal Association of Increased Susceptibility to Viral Haemorrhagic Septicaemia (VHS) in Rainbow Trout (Oncorhynchus mykiss)

Farming of rainbow trout (Oncorhynchus mykiss) in Europe is hampered by unacceptably heavy losses due to the severe infectious disease viral haemorrhagic septicaemia (VHS). Strain-dependent variation of VHS resistance exists. A long-term breeding programme to increase VHS resistance in rainbow trout has been started in Denmark. This programme will be based on experimental VHS challenge of the parental fish (n = 84) as well as their normal and gynogenetic offspring (16 fullsib F1 groups). We found a paternal influence on the average VHS resistance of the offspring; partial regression coefficients for sire-offspring were estimated at 0.30 ± 0.09 and for dam-offspring at −0.1 ± 0.12.

Dietary exposure of rainbow trout ( Salmo gairdneri) to Great Lakes coho salmon ( Oncorhynchus kisutch Walbaum). Bioaccumulation of halogenated aromatic hydrocarbons and host resistance studies

Great Lakes coho salmon ( Oncorhynchus kisutch walbaum) contain a gradient of halogenated aromatic hydrocarbons (HAHs) naturally bioaccumulated from their environment which have immunomodulatory potential. Juvenile rainbow trout ( Salmo gairdneri) were fed diets of coho salmon from Lakes Michigan and Ontario, the Pacific Ocean and control trout chow, for a 20 weak period. The body burdens of organochlorines bioaccumulated in rainbow trout were similar to levels in the dietary coho salmon. The effect on natural resistance was assessed by challenge with a titrated dose of Vibrio anguillarum (VA-58). The ability to mount a protective immune response was determined by immunization with a VA-58 bacterin followed by challenge with virulent VA-58. These parameters of host resistance of rainbow trout were not compromised following dietary exposure to Great Lakes coho salmon.

Effects of 2,3,7,8‐tetrachlorodibenzo‐p‐dioxin (TCDD) or Aroclor 1254 on the resistance of rainbow trout, Salmo gairdneri Richardson, to infectious haematopoietic necrosis virus

Abstract. Sublethal exposure of rainbow trout fry, Salmo gairdneri Richardson, to polychlorinated biphenyls (PCBs) or 2,3,7,8‐tetrachlorodibenzo‐p‐dioxin (TCDD) did not significantly affect mortality or mean time to death following challenge with infectious haematopoietic necrosis virus (IHNV). Rainbow trout fry were fed experimental diets containing 0, 5. 50 or 500 μg/g of the technical polychlorinated biphenyl mixture, Aroclor 1254, for 30 days or were injected intraperitoneally with graded single doses of TCDD. Fish from each treatment group were challenged by immersion exposure to IHNV. At early time points following virus challenge, histopathologic lesions due to virus disease were more severe and occurred more frequently in virus‐challenged fish which received either toxicant than in virus‐challenged control fish. Taken together, these findings suggest that rainbow trout are less sensitive than mammalian species to the sublethal effects of these structurally related toxicants on resistance to viral disease. However, a subtle effect of these chemicals on the pathogenesis of the virus disease is suggested by the histopathologic data.

Seasonal occurrence of the infectious stage of proliferative kidney disease (PKD) and resistance of rainbow trout, Salmo gairdneri Richardson, to reinfection

The seasonality of proliferative kidney disease (PKD) in rainbow trout, Salmo gairdneri Richardson, at the American River Hatchery, California was found to be primarily dependent on the presence or absence of the infectious stage in the water supply. This was determined by introducing sentinel trout into the hatchery water supply on a monthly basis, followed by their transfer to the laboratory for subsequent holding in 18° C, pathogen‐free water for one month prior to examination. These exposures demonstrated that infections were obtained from April through October at ambient temperatures 12–20° C. Trout which had recovered from clinical infections were found to be resistant to reinfection. Resistance was induced by active infection and not just previous exposure to the infectious stage. Trout surviving PKD were also found to harbour later sporogonic stages of the parasite for at least one year following initial infection, but fully formed spores, as judged by well‐developed valves, were not observed.

Selected indices of immunologic resistance in rainbow trout (Salmo gairdneri Rich.) during prolonged, subacute phenolic intoxication

Blastic transformation of the lymphocytes in peripheral blood and spleen, analysis of immunocompetent cells in the blood and haematopoietic organs of rainbow trout after phenolic intoxication (2 mg/dm3, 2 months, winter).

Thermal resistance of juvenile salmonids sublethally exposed to nickel, determined by the critical thermal maximum method

The thermal resistance of juvenile coho salmon (Oncorhynchus kisutch) and rainbow trout (Salmo gairdneri) sublethally exposed to nickel was subsequently examined by the critical thermal maximum (CTM) method. Tests were conducted at a temperature increase rate of 6°C/h, usually 24 to 48 h after chemical exposure. Exposure and initial test temperatures were 15°C for coho salmon and 8°C for rainbow trout. Comparisons with unexposed controls were based on time and temperature of loss of equilibrium and death. Exposure to as low as 1·5 mg/litre nickel for 7 to 21 days significantly suppressed resistance of rainbow trout to elevated temperatures, but 28-day exposure to 0·9 mg/litre nickel did not. Suppressed thermal resistance corresponded to a twofold increase of nickel burden in gill and liver tissue of exposed rainbow trout. Resistance was also suppressed for coho salmon surviving a 14-day exposure to higher, lethal nickel concentrations, but this was not statistically validated. Since sublethal exposure to nickel, one of the least toxic of the metals, lowered fish resistance to elevated temperatures, the same response might be induced by the more toxic metals. One deviant test showed lowered thermal resistance in rainbow trout exposed to 0·06 mg/litre chlorine for 14 days. The CTM method is an efficient and sensitive way of quantifying the thermal resistance of fish sublethally exposed to chemical stressors.

Thermal Resistance of Rainbow Trout from a Permanently Heated Stream, and of Two Hatchery Strains

Abstract Resistance times to high temperatures were determined for fingerling and juvenile rainbow trout (Salmo gairdneri) from the Firehole River, Yellowstone National Park, and from the Ennis and Winthrop hatchery strains, after acclimation to 5, 9, 13, 17, 21, and 24.5°C. Firehole and hatchery trout acclimated to 21 and 24.5°C had similar median resistance times and upper incipient lethal temperatures. After acclimation to the lower temperatures of 5, 9, 13, and 17°C, Firehole trout had longer median resistance times and slightly higher upper incipient lethal temperatures than did the hatchery trout. The ultimate upper incipient lethal temperature for the Firehole trout and for both hatchery strains was about 26.2°C. Rainbow trout inhabiting and reproducing in the heated waters of the lower Firehole River do not appear to have developed the ability to acclimate to higher temperatures.

Cryptobia catostomi: Incubation in plasma of susceptible and refractory fishes

The mechanism of resistance of rainbow trout to Cryptobia catostomi was studied in laboratory raised fish using the in vitro plasma incubation test. In this test a suspension of washed C. catostomi was incubated in freshly collected plasma for 3 hr at 4 C; after that, the mixture was examined for living C. catostomi. The plasma of six refractive fishes (goldfish, creek chub, hornyhead chub, rainbow trout, pike, and brown bullhead) had cryptobiacidal titers ranging from 1:2 to greater than 1:16. Heat inactivation (56 C for 30 min) of the trout plasma reduced the cryptobiacidal titer from 1:16 to 1:4. Selected removal of Mg 2+ and Ca 2+ ions from the plasma using EGTA and EDTA reduced the titer to 1:2 and 1:4; however, the titer was restored to 1:16 when the chelated plasmas were resupplemented with the ions. Zymosan treatment of the plasma also reduced the titer to 1:4. Even partial coagulation of the blood reduced the titer; the titer for serum was only 1:4 as compared to 1:16 for plasma. It is proposed that rainbow trout is refractive to C. catostomi because its blood contains a natural properdin system that is activated by the parasite. Thus the alternate pathway of complement activation is suggested as one of the mechanisms of “natural immunity” by vertebrates that are related to the susceptible host.

Resistance of rainbow trout to ulcerative dermal necrosis.

THE susceptibility of rainbow trout to ulcerative dermal necrosis1, an infectious disease of some salmonids, has become a matter of importance to fish farmers. We have shown that the aetiological agent of ulcerative dermal necrosis is filterable2 although some workers have suggested that specific bacteria3,4 or fungi5 may be the primary pathogens. Preliminary experiments indicated that rainbow trout exposed to a salmon affected by ulcerative dermal necrosis did not show symptoms of the disease whereas a healthy salmon in the same tank as the trout did. The siphoning technique successfully used to reproduce ulcerative dermal necrosis in salmon2 was adapted to the experiments described here, which were designed to ascertain the susceptibility of rainbow trout to the disease. Further experiments, also described, were carried out to show whether rainbow trout can act as symptomless carriers.

The effect of temperature on the acute toxicity of phenol to rainbow trout in hard water

The resistance of rainbow trout to poisoning by phenol increases with increase in temperature up to at least 18° C, at which temperature the 48-hr LC50 is almost twice that at 6° C. A similar relationship exists with gas-liquor phenols. The response of test populations showed the least variability at 12° C.