Brook charr, Salvelinus fontinalis (Mitchill), and cryptobiosis: a potential salmonid reservoir host for Cryptobia salmositica Katz, 1951

Abstract. Laboratory-raised Cryptobia -susceptible brook charr, Salvelinus fontinalis (Mitchill), and rainbow trout, Oncorhynchus mykiss (Walbaum), were vaccinated intraperitoneally with a live Cryptobia salmositica vaccine (250000 parasites per fish), and 4 weeks later were challenged with the pathogen (250000 parasites per fish). Unvaccinated and infected brook charr had high parasitaemias but no clinical signs of disease, while unvaccinated and infected rainbow trout had anaemia and general oedema. Vaccinated and challenged fish had very low parasitaemias compared to unvaccinated and infected brook charr and rainbow trout. Complement fixing antibodies were detected in vaccinated and challenged fish 2 weeks after challenge. Unvaccinated and infected brook charr had consistently higher litres of complement fixing antibody than unvaccinated and infected rainbow trout. Parasitaemias were lower in all fish in which titres of complement fixing antibody were high. In a second experiment, brook charr inoculated intraperitoneally or intramuscularly with 100000 C. salmositica per fish had high parasitaemias but no anaemia or other clinical signs. The results show that susceptible brook charr do not suffer from cryptobiosis and may serve as reservoir hosts for C. salmositica in areas where the disease is prevalent. Vaccination to reduce the parasitaemia when fish become infected may be a control strategy in these areas.     

Interaction between ovine growth hormone and triiodo-L-thyronine on metabolic reserves of rainbow trout,Salmo gairdneri

Rainbow trout (Salmo gairneri) were given slow-release coconut oil implants which contained triiodo-L-thyronine (T3) and were subsequently administered ovine growth hormone (oGH) (either 0.24 or 2.5 g/g body weight) or saline every seventh day for four injections. The purpose of the study was to examine the interactions between oGH and T3 on several aspects of the metabolism in rainbow trout.Trout treated with T3 alone had higher carcass water content, lower liver glycogen, higher plasma T3 levels and lower plasma cholesterol, triglyceride and protein levels compared with the controls implanted with coconut oil implants alone. Trout treated with oGH alone had higher condition factors, lowered carcass total lipid content, elevated liver lipid and RNA content, and elevated plasma T3 and L-thyroxine (T4) levels compared with the coconut oil-implanted and saline-injected controls. Trout treated with T3 and oGH had lower liver glycogen content, higher plasma T3 and fatty acid levels and lower plasma T4, cholesterol and triglyceride levels compared with the controls given coconut oil implants and saline injections alone. There were no apparent effects of either hormone alone or in combination on liver: body mass ratios, liver DNA content, liver RNA:DNA ratios, liver RNA:protein ratios, liver protein:DNA ratios and liver protein content.The data suggest an interaction between oGH and T3 as regards the regulation of condition factor, carcass water content, carcass and liver total lipid content, liver RNA content, plasma fatty acid and plasma protein content.     

Vaccination of rainbow trout, Oncorhynchus mykiss (Walbaum), against cryptobiosis: efficacy of the vaccine in fresh and sea water

Adult rainbow trout, Oncorhynchus mykiss (Walbaum), maintained in either fresh or sea water were vaccinated with a live Cryptobia salmositica vaccine. All vaccinated fish were protected 4 weeks later against the cryptobiosis, while unvaccinated rainbow trout developed the disease (e.g. high parasitaemia and severe anaemia) after challenge with virulent C. salmositica . There was also no disease in vaccinated fish when they were transferred from fresh to sea water immediately after vaccination. Complement fixing antibodies (CFAbs) were detected in vaccinated fish and the CFAbs lysed parasites under in vitro conditions. The antibody titres increased rapidly at one week post-challenge in vaccinated fish in fresh water and vaccinated fish transferred from fresh water to sea water after vaccination. However, the production of CFAbs was delayed by one week in vaccinated fish in sea water and the antibody titre was significantly lower than that in fish maintained in fresh water.     

An enzyme-linked immunosorbent assay (ELISA) for the detection of antibodies against the pathogenic haemoflagellate, Cryptobia salmositica Katz, and protection against cryptobiosis in juvenile rainbow trout, Oncorhynchus mykiss (Walbaum), inoculated with a live vaccine

Abstract. An enzyme-linked immunosorbent assay using dried blood on filter paper, was developed for the detection of antibodies against the haemoflagellate Cryptobia salmositica in juvenile rainbow trout, Oncorhynchus mykiss (Walbaum). Each fish (average weight about 5g) in three experimental groups was either inoculated with 20000 attenuated live C. salmositica vaccine, or inoculated with 2000 or 20000 pathogenic parasites per fish. The vaccine was effective in protecting juvenile trout 4 weeks after vaccination and antibody titers were higher in vaccinated and challenged fish than in unvaccinated and infected ones. Specific antibodies were detected one week post-infection (w.p.i.) with the pathogen and declined to low levels at 6 w.p.i. The high-dose group (20000 per fish) had antibody titres comparable to those of the vaccinated and challenged fish.     

Effects of chronic exposure to γ-HCH (Lindane) on brain serotonergic and gabaergic systems,and serum cortisol and thyroxine levels of rainbow trout,Oncorhynchus mykiss

Rainbow trout (Oncorhynchus mykiss) were implanted intraperitoneally with 0.5 ml.100 g^–1 body weight of coconut oil alone (controls) or coconut oil contaning 0.05 mg of -HCH (Lindane). After 18 days, changes in brain serotonin and GABA metabolism, as well as in serum cortisol and thyroxine levels, were measured. A lower final body weight was observed in -HCH treated fish when compared with control fish. No significant differences were found for serum thyroxine levels between control and treated fish, but a significantly higher cortisol level was found in the -HCH-implanted trout. Although GABA levels did not differ significantly in any brain region in the two treatment groups, the activity of the serotonergic system was significantly altered by the pesticide in both the hypothalamus and the telencephalon.     

Impact of a pathogenic haemoflagellate, Cryptobia salmositica Katz, on the metabolism and swimming performance of rainbow trout, Oncorhynchus mykiss (Walbaum)

Abstract. Oxygen consumption of juvenile rainbow trout (5 g at 13°C) at moderate swimming speeds did not change significantly when infected with Cryptobia salmositica. However, significant reductions of as much as 44% of the maximum aerobic scope for activity and 24% of the critical swimming speed were observed when the parasitaemia reached a maximum of 57.6 × 10⁶ ml⁻¹ fish blood at 3 weeks post- infection. Blood haematocrit was significantly reduced from the initial 34.1 to 19.7% at 4 weeks post- infection, probably as a result of haemolysis by the parasite. The destruction of red blood cells clearly led to lower oxygen carrying capacity, and reduced respiratory and swimming performance.     

Immunosuppression in rainbow trout, Salmo gairdneri Richardson, caused by the haemoflagellate Cryptobia salmositica Katz, 1951

Abstract. An experimental Cryptobia salmositica infection in rainbow trout, Salmo gairdneri Richardson, produced suppression of the humoral response against sheep red blood cells as measured by direct haemagglutination. Two-month and 5-month infections produced equal suppression. The parasite also produced suppression of the humoral response against a bacterial pathogen, Yersinia ruckeri . Anti- Y. ritckeri titres were significantly lower in most fish infected with C. salmositica than in non-infected fish. Immunosuppression became evident when C. salmositica first appeared in the blood (first 2 weeks of infection), Immunosuppression was confirmed by challenge with Y. ruckeri . Mortality at challenge occurred in 64·3% to 83·3% of the fish already infected with C. salmositica at the time of initial Y. ruckeri exposure. There was no mortality at challenge if fish were not infected with C. salmositica at initial bacterial exposure, nor in those concurrently infected with both pathogens. Antigenic competition may have caused the immunosuppression.     

Effect of replacements of fishmeal and fish oil on growth and dioxin contents of rainbow trout

Eight experimental diets were prepared to determine the effect of replacements of fishmeal and fish oil with plant protein and palm oil on the growth and dioxin contents in rainbow trout. The first four diets (FP0, FP5, FP10, and FP15) included fishmeal (55%) with increasing replacement of fish oil by palm oil (0, 5, 10, and 15%). Four other diets (AP0, AP5, AP10, and AP15) were substituted with an alternative protein source and with increasing palm oil content (0, 5, 10, and 15%). Dietary dioxin contents increased as fish oil level increased. Thirty rainbow trout (mean weight 38 g) were fed the experimental diets for 12 weeks. No significant differences in growth performance and feed utilization were observed. Dietary dioxin contents influenced the dioxin contents in the whole body. These results suggest that palm oil could effectively replace fish oil in rainbow trout diets, and reduce the dioxin contents in fish.     

Cortisol-induced changes in oxygen consumption and ionic regulation in coastal cutthroat trout (Oncorhynchus clarki clarki) parr

The influence of cortisol on oxygen consumption and osmoregulatory variables was examined in coastal cutthroat trout (Oncorhynchus clarki clarki) parr kept in fresh water (FW) and transferred to seawater (SW). Intraperitoneal implants containing cortisol (50 g g^–1) in vegetable oil resulted in elevated plasma cortisol titres similar to those observed in fish following a 24h SW exposure. Cortisol treatment significantly increased the oxygen consumption and plasma glucose levels of trout in FW, consistent with the glucocorticoid role of cortisol. Cortisol treatment did not cause any changes in plasma ion concentrations or gill Na⁺,K⁺-ATPase activity in FW after 10 days. Cortisol-implanted fish exposed to SW for 24h showed slightly improved ion regulatory ability compare to non-implanted controls. The results of this study suggest that during SW transfer in juvenile salmonids, increases in cortisol may act as both a mineralocorticoid and a glucocorticoid, depending on the developmental state of the fish (e.g., smolt versus parr). Furthermore, the relative energetic costs of osmoregulation and that of the stress associated SW transfer cannot be discerned using whole-animal oxygen consumption rates.     

Influence of reward level on vertical distribution and growthof rainbow trout Oncorhynchus mykiss fed on demand with self-feeders

ABSTRACT:   The influence of reward level on vertical distribution and growthwas examined in rainbow trout fed on demand with self-feeders. Groupsof 15 trout with initial body weight of 140 g were maintainedat 14°C and feed access was restricted to a 12-h photophase.The trout received three reward levels with triplicates: 0.051 (low),0.089 (medium) and 0.267 g/kg fish/triggeractuation (high). Vertical distribution in the higher reward groupswas generally more even than that in the lower-reward groups, butthe behavioral characteristics of some individuals in a group couldplay an important role in determining vertical distribution. Moreover,no fish including the individuals responsible for trigger actuation,occupied the vicinity of a trigger. The small groups of 15 troutreceiving the medium-reward level obtained as much feed and grewas fast as the high-reward groups, but this was not the case forthe low-reward groups.     

Biological characterization of a monoclonal antibody against a surface membrane antigen on Cryptobia salmositica Katz, 1951

A monoclonal antibody (IgG 1) (designated as MAb-001) was produced against the pathogenic haemoflagellate Cryptobia salmontica Katz. The antibody agglutinated live parasites under in vitro conditions. Live C. salmositica, incubated with MAb-001 at 10 °C, did not multiply and were dead within 4 weeks in culture. About 50% of juvenile rainbow trout, Oncorhynchus mykiss (Walbaum), inoculated intraperhoneally with C. salmositica, incubated in MAb-001 prior to inoculation, did not become infected, while in adult rainbow trout, the peak parasitaemia was reduced. These results indicate that MAb-001 is a protective monoclonal antibody and the antigen it recognizes is located on rhe surface membrane of C. salmositica. The antibody also inhibits multiplication and affects viability of the parasite under in vitro conditions.     

Cortisol does not affect hepatic α- and β-adrenoceptor properties in rainbow trout (Oncorhynchus mykiss)

Distribution and function of hepatic - and -adrenoceptors were examined in rainbow trout (Oncorhynchus mykiss) injected with slow release hydrogenated coconut oil implants alone (sham) or containing cortisol. - and -Adrenoceptors were assayed on purified hepatic membranes 10–14 days post-implantation using ³H-prazosin () and ³H-CGP (). At 10–14 days, plasma cortisol values were significantly elevated to approximately 220 compared with 35.0 ng ml^-1 in cortisol implanted vs. sham trout. No significant differences were found between any of the experimental groups for either the affinity (K_d) or maximal number of binding sites (B_max) for either receptor type. Epinephrine significantly stimulated glucose release from hepatocytes isolated from sham injected trout, but not from cortisol-treated fish. Epinephrine-induced glucose release was blocked by both - and -antagonists. These studies do not support the hypothesis that rainbow trout exposed to chronic cortisol alter properties of hepatic adrenoceptors.     

Intraperitoneal injection of sulfur amino acids enhance the hepatic cysteine dioxygenase activity in rainbow trout (Oncorhynchus mykiss)

As part of the investigation into cysteine metabolism in fish, sulfur amino acids and their derivatives were injected intraperitoneally to fingerling rainbow trout (Oncorhynchus mykiss) to examine how the doses of these compounds affect the hepatic cysteine dioxygenase [EC 1.12.11.20] in this species. A dose of 0.25 mmol L-cysteine per 100 g body weight induced the enzyme activity as much as 2.5 times that of the control fish within 4h after the injection. The activity increased proportionally to the increasing dose of cysteine up to the dose of 0.15 mmol per 100 g body weight. The induction was observed to be rather specific to L-cysteine. These findings suggested that the cysteine sulfinate pathway might play an important role in the metabolism of excess cysteine in rainbow trout. The dosage of L-cysteine larger than 0.50 mmol per 100g body weight led to mortality of the fish. The pathway of cysteine catabolism was considered to function to prevent toxic accumulation of cysteine in rainbow trout, as in the case of mammals.     

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...     

Evaluation of Experimental and Practical Diets for Bluegill Lepomis macrochirus and Hybrid Bluegill L. cyanellus × L. macrochirus

Two experiments were conducted to identify appropriate experimental and practical diets for bluegill Lepomis macrochirus and hybrid bluegill L. cyanellus × L. macrochirus reared in aquaria. In the first study, four experimental diets and five commercial diets were evaluated in juvenile hybrid bluegill initially weighing 4.8 g/fish. The experimental diets contained casein (CAS), casein + gelatin (CAWGEL), casein + L‐arginine‐HCI (CAS/ARG), or casein + gelatin + crystalline amino acids (CAS/AA) as sources of crude protein. The commercial diets included three diets formulated to meet the nutritional requirements of rainbow trout Oncorhynchus mykiss and two diets formulated to meet the nutritional requirements of channel catfish Ictalurus punctatus. Each diet was fed twice daily at a rate of 4% of body weigh/d to triplicate groups of fish. At the end of the 8‐wk feeding trial, weight gain was significantly higher in fish fed the best commercial rainbow trout diets (205–217%) compared to fish fed diets formulated for channel catfish (87–104%). Weight gain and feed efficiency (FE) of fish fed the experimental diets (5346% and 0.19–0.32, respectively) were significantly lower than those of fish fed the commercial rainbow trout diets (143–217% and 0.49–0.64, respectively). In the second experiment, the same dietary treatments were fed for 8 wk to juvenile bluegill initially weighing 3.7 g/fish. Each diet was fed twice daily at a rate of 4% of body weight/d to triplicate groups of fish. Weight gain was significantly higher in fish fed commercial trout diets (291–402%) compared to fish fed diets formulated for channel catfish (164–191%). Weight gain and FE of fish fed CAS/ARG were significantly higher than those of fish fed the commercial catfish diets, but significantly lower than those of fish fed the best commercial trout diets. Results of this study indicate that commercial rainbow trout diets are preferable to commercial channel catfish diets for culture of bluegill and hybrid bluegill. More research is needed to identify appropriate experimental diets for this group of fishes.     

Enhancing highly unsaturated ω‐3 fatty acids in phase‐fed rainbow trout (Oncorhynchus mykiss) using Alaskan fish oils

Rainbow trout, average weight 185–187 g, were fed feeds containing menhaden oil, canola oil or fish oils (pollock, pink salmon or rockfish) produced from Alaskan seafood processing waste as the added oil for 8 weeks, at which time the fish weighed 391–411 g (average 404 g, pooled SE = 5.7). The fish were previously fed from 75 g average weight fed commercial feed containing poultry oil as the added oil. No significant differences were measured in final weight or feed conversion ratio among dietary treatment groups. Significant differences were found in fillet ω‐3 fatty acid (FA) levels from fish receiving fish oil‐supplemented feeds compared to those from fish receiving feeds containing canola oil. Fillet contents of eicosapentaenoic acid (EPA; 20:5ω3) and decosahexaenoic acid (DHA; 22:6ω3) were highest in the pollock oil treatment group, although all fish oils increased highly unsaturated ω‐3 FA contents (mg 100 g^?1) of fillets. Fish oil used through the production cycle was reduced by 25% by supplementing feeds with poultry oil during the middle phase of production (75–175 g) compared to using feeds containing fish oil throughout the production cycle. Fish oils recovered from Alaskan seafood processing waste were suitable alternatives to conventional fish oil as ingredients in rainbow trout production feeds.     

Effect of Dietary Safflower and Canola Oil on Growth Performance,Body, and Fatty Acid Composition of Rainbow Trout (Oncorhynchus mykiss)

The objective of the present study was to evaluate the effects of the diets enriched with safflower and canola oil on growth, feed utilization, body composition, liver, and muscle fatty acid composition of rainbow trout (Oncorhynchus mykiss). Rainbow trout having approximate initial weight of 97.03 ± 0.10 g were fed the experimental diets containing only fish oil (Group 0SFO), safflower oil (50% safflower oil, Group 50SFO and 33% safflower oil, Group 33SFO), and vegetable oil blend (33% safflower and 33% canola oil, Group 66SFCO) for 45 days. Twenty-five fish were randomly assigned for triplicate treatments and offered the test diets two times daily to apparent satiation. At the end of the experiment, survival was 100% in all treatments. No significant differences in the weight gain, specific growth rate, feed conversion ratio, and protein efficiency ratio were found between fish fed with the different experimental diets. The highest hepatosomatic index (HIS) and viscerasomatic index (VSI) was obtained in 50SFO and 33SFO groups, respectively. The moisture, protein, lipid, and ash content in the body composition of the fish increased in all experimental groups. The lipid content was not significantly different among the groups (p > 0.05); however, there was a significant difference in ash content between the control and the other groups (p < 0.05). The experimental diets containing vegetable oil (50SFO and 33SFO groups) and vegetable oil blend (66SFCO group) had significantly higher concentrations of n-6 fatty acids, predominantly in the form of linoleic acid (LA). The n-3 fatty acids were present in significantly higher concentration in the control treatment (0SFO). The fatty acid composition of fish fillet and liver were reflective of the dietary lipid source. While the fillet and liver of fish fed the 50SFO diet was high in linoleic acid (18:2 n-6), fish fed the 66SFCO diet had high concentrations of oleic acid (OA; 18:1 n-9). The present study suggests that fish oil can be replaced by up to 50% with safflower oil and by up to 66% with safflower + canola oil blend in rainbow trout diets with no significant effect on growth.     

Plasma levels of insulin,glucagon and glucagon-like peptide in salmonids of different weights

Plasma levels of insulin in rainbow trout,Oncorhynchus mykiss, Atlantic salmon,Salmo salar, and Pacific coho salmon,Oncorhynchus kisutch and plasma circulating levels of glucagon and glucagon-like peptide, in rainbow trout and Atlantic salmon, were measured by homologous radioimmunoassays. Hormonal levels were compared against the average body weight of the same group of fish. Plasma insulin levels were significantly correlated (r=0.56, 0.46 and 0.42 respectively) with body weight in all three salmonid species. Moreover, rainbow trout from fast-growing families had significantly higher (p<0.005) plasma insulin levels than did fish from slow-growing families. Plasma titres of glucagon and glucagon-like peptide were always lower than insulin titres and did not correlate with body weight.Reported in part at Satellite Symposium on Applications of Comparative Endocrinology to Fish Culture, Almunecar, Spain (Sundby, 1989).     

Changes in Dietary Protein to Metabolizable Energy Needs of 17α-Methyltestosterone Treated Juvenile Rainbow Trout1,2

Two consecutive feeding trials were used to examine optimum dietary protein to metabolizable energy (P:ME) and ME needs of juvenile rainbow trout fed semipurified diets supplemented with 2.0 mg 17^α-methyltestosterone (MT)/kg of dry ingredients. In trial 1, five diets containing 80,100, 120, 140, and 160 mg protein/kcal ME of dry diet at a constant 390 kcal ME/100 g of dry diet were used. In trial 2, four diets were prepared with 300, 340, 370, and 390 kcal dietary ME at a P:ME ratio of 100. Diets were prepared with and without MT and fed for 8 weeks to 5.4 g initial weight fish in trial 1 and 3.7 g initial weight fish in trial 2. Proximate composition of the whole body (WB) and empty carcass (EC = an eviscerated whole body) of fish was measured at the end of both trials. In trial 1, maximum efficient protein gain (MEPG) values of MT treated fish were correspondingly higher than the values obtained for controls at all dietary P:ME ratios fed except for those fish fed at a P:ME ratio of 80. The optimum P:ME ratio for MT treated fish was 100 and for control fish was 120. In trial 2, all MT treated fish fed diets containing 340 kcal ME/100 g and above had a higher MEPG value than all control fish. The diet containing an ME level of 340 kcal was considered optimum for growth of MT treated fish fed a dietary P:ME ratio of 100. MT treatment increased EC, but did not change WB fat content of fish in both trials.     

The immune response of rainbow trout, Salmo gairdneri Richardson, to the haemoflagellate, Cryptobia salmositica Katz, 1951

Abstract. Rainbow trout that recovered from experimental Cryptobia salmositica infection 6 and 10 weeks earlier were protected against multiple intraperitoneal challenges of 50 000 and 10 000 parasites isolated from infected fish. The immunity was non-sterile; low parasitaemias were detected following a larger challenge (112 000 parasites). The indirect haemagglutination test was used to detect C. salmositica -specific agglutimns. Antibody titers increased during the first 18 weeks of infection. The infectivity of cultured C. salmositica was neutralized by incubation in heat-inactivated immune plasma. Infectivity of C, salmositica from infected fish was not neutralized by similar treatment. Complement fixing antibody was detected using the in vitro immune lysis test. Immune lysis occurred when cultured C. salmositica were used. Adoptive transfer of both leucocytes and plasma from immune fish conferred partial protection against the parasite in naive recipients. Complement fixing antibody may be important during early acute infection while phagocytosis may be important during the later chronic phase.