Effect of protein source on the reproductive performance of female rainbow trout, Oncorhynchus mykiss (Walbaum)

Two-year-old rainbow trout, Oncorhynchus mykiss (Walbaum), females were fed three different diets containing animal protein R1 or vegetable protein R2 and R3 over 12 months from March 1993 until February 1994. Diets containing vegetable protein slightly depressed broodstock growth rates, although the final weight differences among groups were not statistically significant. The mean total fecundity (eggs female^?1) was significantly higher (P<0.05) in group R1. With regard egg composition, amino acids levels in group R3 were significantly lower (P<0.05) than in the other groups. Although the total amino acids of eggs from the R1 and R2 groups presented a similar pattern, the essential amino acids lysine, threonine, cystine and isoleucine were lower in the R2 group. The ω 6 and ω3 fatty acid levels of the eggs were also affected by the protein source of the diet. In both the R2 and R3 groups, the plasma levels of 17β-estradiol reached a maximum level one month later than the R1 group. For the R2 and R3 groups, plasma levels of vitellogenin peaked after a one-month delay; peak values were significantly lower (P< 0.05) than in the R1 group. Similarly, the vitellogenin content of the eggs was in accordance with plasma levels in broodstock females. The results of the present study demonstrated that the composition of diet significantly affected reproductive indices and composition of the eggs.     

Immunogenicity of amoebic antigens in rainbow trout, Oncorhynchus mykiss (Walbaum)

Abstract. Rainbow trout developed a humoral immune response against numerous antigens of sonicated amoebae which were emulsified with Freund's complete adjuvant and injected into the peritoneum. The amoebae were cultured from the gills of Atlantic salmon, Salmo salar L., affected by amoebic gill disease. Antibodies in fish sera were detected by both enzyme-linked immunosorbent assay (ELISA) and immunoblotting. Non-spedfie reactivity in fish serum against Escherichia coli, the bacterium used in co-cultivation of amoebae in vitro, was removed by immunoadsorption. Results obtained using ELISA and immunoblotting were comparable and indicated no significant difference in response to immunization with 10, 50 or 250 μg of sonieatcd amoebic protein. Amoebae contained immunogenie components of > 100, 100, 89, 49, 37 and 34kDa.     

Virulence of Flavobacterium psychrophilum isolates in rainbow trout Oncorhynchus mykiss (Walbaum)

Flavobacterium psychrophilum, the causative agent of bacterial cold‐water disease (BCWD) in freshwater‐reared salmonids, is also a common commensal organism of healthy fish. The virulence potential of F. psychrophilum isolates obtained from BCWD cases in Ontario between 1994 and 2009 was evaluated. In preliminary infection trials of rainbow trout juveniles, significant differences (0% to 63% mortality) in the virulence of the 22 isolates tested were noted following intraperitoneal injection with 10⁸ cfu/fish. A highly virulent strain, FPG 101, was selected for further study. When fish were injected intraperitoneally with a 10⁶, 10⁷ or 10⁸ cfu/fish of F. psychrophilum FPG 101, the 10⁸ cfu/fish dose produced significantly greater mortality (p < 0.05). The bacterial load in spleen samples collected from fish every 3 days after infection was determined using rpoC quantitative polymerase chain reaction amplification and by plate counting. Bacterial culture and rpoC qPCR were highly correlated (R² = 0.92); however, culture was more sensitive than the qPCR assay for the detection of F. psychrophilum in spleen tissue. Ninety‐seven per cent of the asymptomatic and the morbid fish had splenic bacterial loads of <2.8 log₁₀ gene/copies and >3.0 log₁₀ gene copies/reaction, respectively, following infection with 10⁸ cfu/fish.     

Oxygen-induced gas bubble disease in rainbow trout, Oncorhynchus mykiss (Walbaum)

Abstract. An Aquatector oxygen injection unit was used to supersaturate a hatchery water supply to 200% oxygen saturation (18–20mg/l) and increase the total gas pressure to 120% of saturation. Nitrogen saturation was reduced to near 100%. Rainbow trout, Oncorhynchus mykiss (Walbaum), held in the treated water developed signs of gas bubble disease in 4 days, and 50% died within 20 days. We demonstrated that supersaturated total gas pressure due to excessive oxygen saturation causes gas bubble disease in the absence of supersaturated nitrogen gas. It is recommended that users of oxygen injection systems closely adjust the amount of oxygen added to the water to keep the total gas pressure near saturation.     

Effects of dietary keto-carotenoids (canthaxanthin and astaxanthin) on the reproductive performance of female rainbow trout Oncorhynchus mykiss (Walbaum)

The aim of this study was to clarify further the relationship between dietary keto-carotenoids (canthaxanthin and astaxanthin) and reproductive performance in female rainbow trout. Three experiments were undertaken in three successive breeding seasons. In addition to a control diet, fish were fed a canthaxanthin-supplemented diet (200 mg canthaxanthin kg⁻¹ feed, designated as 6mC200) for 6 months prior to spawning (experiment A); the same diet as in A but for either 3 months (3mC200) or 6 months (6mC200) before spawning (experiment B); diets with one of two levels of astaxanthin supplementation, 50 mg (6mA50) or 100 mg (6mA100) kg⁻¹ feed, or a diet with 100 mg canthaxanthin kg⁻¹ feed (6mC100) fed for 6 months (experiment C).
There was no significant influence of carotenoid supplementation on either the frequency of maturing females or the date of maturation. The number of ova per kg of female body weight averaged 2700 and did not vary significantly among fish fed the different diets. Across experiments A, B and C there was no significant difference in egg and larval survival among fish fed carotenoid-supplemented and control diets. In experiment A, 6mC200 females produced smaller eggs than controls but this result was not confirmed in experiments B and C. In general, eyed egg yield appeared partly dependent upon egg size. Alevin weight was also correlated with egg weight. The growth test conducted on fingerlings from experiment B failed to provide any evidence of an effect of feeding carotenoid supplemented diets to the female parent. Pigment analyses conducted on alevins revealed that canthaxanthin fed to the female parent was transferred into the eggs and therefore to the larvae, although canthaxanthin was metabolized within a few weeks after hatching.     

Indirect estimation of stomach volume of rainbow trout Oncorhynchus mykiss (Walbaum)

The main hypothesis of this study was that if stomach volume is correlated with food intake it can be estimated without laborious and destructive direct measurement. Rainbow trout, Oncorhynchus mykiss (Walbaum), ca. 500–1300 g, were starved for 1, 4, 8 or 16 days at 15°C after which they were fed in excess with dry pellets containing known amounts of X‐ray‐dense markers. Immediately after feeding the fish were killed, X rayed and weighed. Then the stomach was dissected, its contents removed and weighed, and stomach volume was measured. X‐ray plates were developed and feed intake was estimated based on the amount of marker. All measured variables correlated positively with stomach volume. The best fit for linear regression models was obtained for fish starved for 4 days, where stomach content (dry mass) explained 94%, food intake (based on X‐ray measurement) 77% and fish mass 62% of the variation in stomach volume. However, as stomach content measurement can be a lethal, or at least very stressful, event for the fish, the accuracy of food intake measurement (X‐ray) could be increased using multiple regression. In multiple linear regressions, R²‐values varied between 0.79 (16‐day starvation) and 0.91 (1‐day starvation) with food intake and fish mass as explanatory variables for stomach volume. These results indicate that the stomach volume in rainbow trout can be estimated satisfactorily using indirect methods, which are not detrimental to the fish, although feeding history may affect the accuracy of the estimates.     

Computer-controlled freezing of rainbow trout Oncorhynchus mykiss (Walbaum) spermatozoa for routine programmes

The effects of extender composition and freezing rate on cryopreservation efficiency of refrigerated spermatozoa of rainbow trout Oncorhynchus mykiss (Walbaum) were evaluated in order to test the suitability of a computer-controlled ultrafreezer to cryopreserve milt samples obtained in field conditions and stored for several hours. A very highly significant first-order interaction between freezing rate and the type of extender was found. Six of the eight experimental variants did not differ significantly, resulting, after fertilization of eggs with cryopreserved sperm, in a range of 62.3–74.8% of eyed embryos. This procedure was effective for samples stored at 1 °C for 2 days.     

Use of probiotics to control furunculosis in rainbow trout, Oncorhynchus mykiss (Walbaum)

Aerobic heterotrophic bacteria were isolated from the intestinal contents of Atlantic salmon, Salmo salar , rainbow trout, Oncorhynchus mykiss , and turbot, Scophthalmus maximus , on tryptone soya agar and De Man Rogosa and Sharpe agar, of which 11 of 177 (6% of the total) of the isolates were antagonistic to Aeromonas salmonicida . Four of these cultures, which were identified tentatively as A. hydrophila , Vibrio fluvialis , Carnobacterium sp. and an unidentified Gram-positive coccus, were beneficial to fish when fed singly or as an equi-mixture. Feed supplemented with the putative probiotics indicated survival of the organisms in the gastrointestinal tract for 7 days. Feeding with the probiotics for 7 and 14 days led to better survival following challenge with A. salmonicida . There was no indication of serum or mucus antibodies to A. salmonicida , but there was an increased number of erythrocytes, macrophages, lymphocytes and leucocytes, and enhanced lysozyme activity in the fish.     

Attachment of Vibrio pathogens to cells of rainbow trout, Oncorhynchus mykiss (Walbaum)

Abstract. The attachment of Vibrio pathogens to cells of rainbow trout, Oncorhynchus mykiss (Walbaum), was studied by use of species-specific monoclonal antibodies and indirect FITC- immunofluorescence microscopy. Vibrio anguillarum, V. ordalii and V. parahaemolyticus attached to cultured cells of rainbow trout gonads, various tissues of cryostat sections of whole fish, and smears of gills, intestine, buccal mucosa and skin. The attachment was inhibited by prior incubation of bacteria with monoclonal antibodies at titres of 1:32, or less. Other Vibrio pathogens used in this study did not attach to any trout cells. The research provides approaches to study the mechanisms of bacterial attachment in the onset of Vibrio infections.     

Hexamitiasis leads to lower metabolic rates in rainbow trout Oncorhynchus mykiss (Walbaum) juveniles

This study assessed the effects of Hexamita salmonis (Moore) on metabolism of rainbow trout Oncorhynchus mykiss (Walbaum) and its effect on the host's susceptibility to infectious pancreatic necrosis virus (IPNV) after antiparasitic treatment. Rainbow trout naturally infected with H. salmonis were treated with 10 mg metronidazole kg fish^?1 per day, and their physiological recovery was assessed through measuring resting metabolism on the 7th, 14th, 21st and 28th day after treatment. In addition, we exposed the naïve fish to H. salmonis and measured the resting metabolism (oxygen consumption as mg O₂ kg^?1 per hour) on the 10th, 20th and 30th day after the exposure to assess the variation in metabolic rates after infection. Significantly lower rates of metabolic activity (P < 0.05) were anticipated 20 days after infection with H. salmonis compared with the fish infected with H. salmonis for 10 days or with the parasite‐free fish. Similarly, the treated fish needed about 20 days to fully recover from hexamitiasis. The susceptibility of rainbow trout to IPNV remained unchanged in the presence of H. salmonis. Weight loss was significantly higher (P < 0.05) in infected than that in the parasite‐free fish. Fish should be examined regularly for H. salmonis and treated immediately whether found to prevent economic losses and excessive size variation.     

Red blood cell indices of rainbow trout Oncorhynchus mykiss (Walbaum) in aquaculture

A direct non‐parametric method was used to calculate reference (physiological) haematology values for farmed 10–12‐month rainbow trout of the Kamloops strain (mean weight: 330±131 g) with respect to red blood cell counts (RBCc), haematocrit values (Hct), haemoglobin concentrations (Hb), mean corpuscular volume (MCV), mean corpuscular haemoglobin (MCH) and mean corpuscular haemoglobin concentrations (MCHC). The fish in the selected reference group (n=798) were given dry pelleted diets that contained 37–47% crude protein, 7–18% crude fat and 108–300‐mg vitamin E, 1.08–5‐mg folic acid, 0.018–0.05‐mg vitamin B₁₂, 48–64.5‐mg iron, 4.5–8.4‐mg copper and 0.18–0.24‐mg selenium supplied per kg of diet. Ethoxyquin and butylhydroxytoluol were used to protect the fat component against oxidation. The fish were kept at a stocking density of 50kg per cubic metre in tanks provided with running freshwater (dissolved oxygen 8.4–11.5 mg L^?1, with O₂ saturation of 77–98%) at an ambient temperature of 0.2–16°C. Blood was sampled between September and November at a photoperiod of 9–13 h:11–15 h (light:dark). Reference ranges for the preceding haematological indices were as follows in immature females (males): RBCc, 0.77–1.42T L^?1 (T – tera, 10¹²) (0.98–1.55T L^?1); Hct, 0.304–0.502 (0.34–0.546); Hb, 54–93 g L^?1 (59–97 g L^?1); MCV, 282–469 fL (279–434 fL); MCH, 51–86 pg (47–78 pg); MCHC, 0.15–0.22 (0.15–0.2). In males, values for RBCc, Hct and Hb were significantly higher (P=0.01 and 0.0000 respectively) and those for MCV, MCH and MCHC were significantly lower (P=0.01 and 0.0002 respectively) than in immature females. Nutritional and environmental factors affecting erythropoiesis in trout and some correlations between haematological (RBCc, Hb, Hct) and biochemical indices of the blood plasma (total protein, cholesterol) are discussed.     

Preliminary study for description of bone tissue responsiveness to prolonged dietary phosphorus deficiency in rainbow trout,Oncorhynchus mykiss (Walbaum)

Prolonged dietary phosphorus (P) deficiency induces a generalized demineralization of bone tissues; however, the differential responsiveness of the diverse tissues to P deficiency remains unknown. Triploid all‐female juvenile rainbow trout (initial mass ~60 g) were fed two practical diets (0.26% and 0.52% digestible P for P‐deficient and P‐sufficient diets) until P‐sufficient fish reached 850 g (241 days; 12°C; 18:6 D:L). Early P‐deficient fish were fed from day 0 the low P‐diet, while late P‐deficient only started feeding at day 134. Growth performance was assessed monthly and carcass samplings were performed at day 0, 134 and 241 to assess mineralization characteristics of different tissues. Ash and content of phosphorus, calcium and magnesium of scales, operculae, ribs and vertebrae as well as the occurrence of abnormalities in ribs and vertebrae were assessed. The tissues most affected by P deficiency were: vertebrae > scales > opercula > ribs. P deficiency affects bone tissues differentially based on the physiological and biomechanical roles of the tissues. As scales were found to be a better indicator to predict abnormalities, understanding of scale metabolism could facilitate P status estimation in fish.     

The ability of clove oil and MS-222 to minimize handling stress in rainbow trout (Oncorhynchus mykiss Walbaum)

The effects of 60‐mg L^?1 clove oil and 60‐mg L^?1 tricaine methanesulphonate (MS‐222) on the blood chemistry of rainbow trout were compared after exposure to handling stress via caudal puncture blood sampling. Fish sampled by caudal puncture and subsequently exposed to anaesthetics showed a typical handling stress response over a 48‐h period. There were no significant differences between the responses of fish exposed to equal concentrations of clove oil and MS‐222, with the following exceptions: the blood glucose at full anaesthesia, and lactate at full recovery increased significantly in the clove oil‐exposed fish. In a subsequent experiment, the stress response observed in fish sampled by caudal puncture and exposed to clove oil and MS‐222 was compared with a non‐anaesthetized control group. The increases in plasma cortisol levels were significantly lower at recovery in fish treated with either anaesthetic compared with the control fish. Fish exposed to MS‐222 had significantly higher cortisol levels at 1 h. These findings show that few differences exist between the anaesthetic effects of clove oil and MS‐222 on the physiological response of fish to stress. However, clove oil is more effective at reducing the short‐term stress response induced by handling and blood sampling, and is recommended as an alternative fish anaesthetic.     

Relationships between growth and disease resistance in rainbow trout,Oncorhynchus mykiss (Walbaum)

Rainbow trout from 23 families were evaluated for growth and resistance to the bacterial coldwater disease (BCWD) caused by Flavobacterium psychrophilum and infectious haematopoietic necrosis (IHN) caused by IHN virus. Average family weights were between 161 and 263 g with an average of 225 g at 213 days post‐fertilization with specific growth rates ranging from 2.37 to 2.88. Per cent survival of fish challenged with F. psychrophilum was between 18% and 100%, while for those challenged with IHNV, the range was between 12% and 93%. Significant positive correlations were found for end body weight and resistance to IHN (P < 0.05) and for early body weight and resistance to BCWD (P < 0.1). However, no significant correlations were detected between resistance to both pathogens or disease resistance and overall genetic diversity or diversity within the major histocompatibility locus.