Flesh qualities and muscle fiber characteristics in triploid and diploid rainbow trout

Analyzed with regard to their slaughter weights and flesh quality 78‐month‐old diploid and triploid rainbow trout (full sibs) were reared together in a pond after tagging at an age of 12 months. Triploids had higher body weights and carcass percentages than diploids (6 kg vs 4 kg and 66% vs 52%). Triploid fish also displayed lower electrical conductivity values and darker (L* value) and redder (a* value) flesh color. The fillets of the triploid trout contained more crude fat and less moisture than the diploids (6% vs 3% and 68% vs 74%, respectively). No effect of ploidy was found with regard to the protein contents. Triploid rainbow trout had larger mean white and intermediate muscle fiber areas than diploid fish in the dorsal and pelvic fin regions. In the pelvic fin part, the white muscle fiber areas were larger than in the dorsal fin part. In conclusion, adult triploid rainbow trout grow faster especially by fiber hypertrophy and have better flesh quality parameters than diploid fish.     

Effects of whirling disease on selected hematological parameters in rainbow trout

Hematological responses to whirling disease in rainbow trout (Oncorhynchus mykiss) were investigated. Two-mo-old fingerling rainbow trout were exposed to cultured triactinomyxon spores of Myxobolus cerebralis at 9,000 spores/fish in December, 1997. Twenty-four wks post-exposure, fish were taken from infected and uninfected groups for peripheral blood and cranial tissue sampling. Histological observations on cranial tissues confirmed M. cerebralis infection in all exposed fish. Differences in hematological parameters between the two groups included significantly lower total leukocyte and small lymphocyte counts for the infected fish. No effects on hematocrit, plasma protein concentration, or other differential leukocyte counts were noted.     

Red muscle recruitment during steady swimming correlates with rostral-caudal patterns of power production in trout

Rainbow trout (Oncorhynchus mykiss) and brook trout (or charr, Salvelinus fontinalis) display different rostral-caudal patterns of power production by the red or aerobic muscle during steady swimming. The anterior muscle of rainbow trout produces much less power for swimming than the posterior, while in brook trout there is no variation in power output. To determine if red muscle recruitment is associated with anterior-posterior patterns of power production, electromyography (EMG) was used to record red muscle activity at three body positions across a range of swimming speeds in fish of each species. The initial recruitment of the anterior red muscle in swimming rainbow trout was predicted to lag behind, i.e. occur at higher speeds, that of the posterior due to the variation in power production, but no variation in recruitment was expected for brook trout. Burst of red muscle EMG activity occurring with each tailbeat was analyzed for frequency (tailbeat frequency), duty cycle (DC) (duration of burst relative to the period of the tailbeat) and burst intensity (BI) (magnitude of the measured EMG activity). Brook trout swam with higher tailbeat frequencies and longer values of DC than rainbow trout. Both species showed a pattern of longitudinal variation in DC, with longer DC values in the anterior red muscle. BI also differed significantly along the length of rainbow trout but not brook trout. In the former, BI of anterior muscle was significantly less than the posterior at lower steady swimming speeds. The EMG data suggest that power production and muscle recruitment are related. In rainbow trout, where there is longitudinal variation in muscle power output, there are also significant rostral-caudal differences in red muscle recruitment.     

Seasonal variations of lipid fatty acids of boreal freshwater fish species

1. The fatty acid levels of muscle and liver lipids of perch, vendace and rainbow trout (Salmo gairdneri) cultivated in the same area (for comparison) were monitored. 2. The total lipid content in the muscle of perch (Perca fluviatilis) and vendace (Coregonus albula) was less than 50% of that in rainbow trout and a seasonal variation was clear only in vendace. 3. The relative amounts of polyunsaturated fatty acids as well as omega-3 acids were higher in vendace and perch than in cultivated rainbow trouts. Arachidonic acid content was much higher in vendace and perch than in rainbow trout. The content of monoenes was considerably higher in rainbow trout than in free freshwater fish. 4. The seasonal variations in the degree of unsaturation were small in fish muscle. 5. In the muscle of rainbow trout the relative amount of polyunsaturated fatty acids diminished with the increase of total lipids.     

Changes in selected blood component values of rainbow trout, Salmo gairdneri Richardson, following the blocking of the cortisol stress response with betamethasone and subsequent exposure to phenol or hypoxia

Cortisol was undetectable in rainbow trout plasma 24 h after the fish had been injected with betamethasone. This drug is known to suppress ACTH release and, consequently, cortisol production in teleosts. The blood glucose, chloride, sodium, potassium and total protein concentrations were not significantly affected by betamethasone. However, significantly increased blood packed cell volume values were found.
Betamethasone-injected fish when exposed to hypoxia or phenol had a pattern of blood component changes similar to those found in sham-injected fish also exposed to the pollutants. These changes in turn were similar to those found in exposed but uninjected and unhandled fish. Suppression of rainbow trout plasma cortisol concentrations with betamethasone apparently has no effect on the fish's short-term blood component responses to pollutants under the conditions used in these experiments, but does prevent a stressormediated increase in plasma cortisol concentrations.     

An experimental study of ontogenetic and seasonal changes in the temperature preferences of unfed and fed brown trout,Salmo trutta

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Glucose 6-phosphate dehydrogenase in rainbow trout

Electrophoretic analysis of glucose 6-phosphate dehydrogenase from liver and blood of rainbow trout revealed a complex series of bands, which could differ between fish. The partial interconvertible nature of these bands was demonstrated with enzyme that had been incompletely inactivated at pH 8.4. In a single population of 40 fish, a homozygote and a heterozygote for an electrophoretic variant allele were found. We suggest that G6PD in rainbow trout liver and blood is determined by two alleles at a single locus, with posttranslational modification responsible for the complex electrophoretic patterns seen. The basis for this variation appears to be NADH binding to the protein molecule. Another variant and other properties of the enzyme are described.Supported in part by the State of California Department of Mental Hygiene and by USPHS Grants GM-15253, HD-04612, HD-00315, HD-05615, and HL-15125. One of us (S.D.C.) was a Special Postdoctoral Fellow of NIAMD (No. 1F03AM-40, 329-01) during part of this work.     

Important considerations for methaemoglobin measurement in fish blood: assay choice and storage conditions

Spectrophotometric assays of methaemoglobin (metHb) in rainbow trout Oncorhynchus mykiss , channel catfish Ictalurus punctatus , tilapias Tilapia niloticus and Tilapia zillii and white sturgeon Acipenser transmontanus , under baseline conditions, were low (<4%) for each species, and yet higher than human values (<1%). MetHb results for a given fish species varied significantly between assays and two assays were deemed unacceptable for particular animals. For rainbow trout, white sturgeon, and the two species of tilapia, the Dubowski method gave uncharacteristically high estimates of metHb. MetHb could not measured in tilapia blood using the Evelyn & Malloy method due to spectral interference. Only the Horecker & Brackett assay worked well for all species. Storage conditions were extremely important in the quantification of metHb in rainbow trout blood. For consistent values, samples can be stored up to 4 h on ice (0° C) or at least 20 days under liquid nitrogen (− 196° C). Auto-oxidation, however, elevates rainbow trout metHb at − 20 and − 80° C. It should not be assumed that the blood of fishes and humans perform similarly during assays of metHb.     

Circulatory system of rainbow trout Oncorhynchus mykiss (Walbaum): a corrosion cast study

The present study describes and visualizes the circulatory system of rainbow trout with emphasis on the heart and main blood vessels, employing corrosion cast methodology. Ten rainbow trout (Oncorhynchus mykiss (Walbaum) of 1000 g average weight were obtained from a commercial fish farm. Fish were anaesthetised using a benzocain solution in ethanol. After 40 min, the fish were killed using an overdose of the benzocain solution. The aorta caudalis and aorta coeliaco‐mesentric were cannulated and attempts were made to fill the blood vessels and heart with fluid artificial resin made on the basis of methylmetacrylate. The fish were further prepared by submersion for 12–24 h in a room temperature waterbath until polymerisation and hardening of the methylmetacrylate was complete. This was followed by 24–48 h submersion in a 25% solution of KOH to obtain full maceration of the organic tissues. Various parts of the heart and blood vessels were retained in their natural positions, thereby demonstrating the anatomical details of the main circulatory system. Main elements depicted included the sinus venosus, atrium, ventricle, bulbus arteriosus and related vessels such as the dorsal aorta, subclavian vein, hepatic vein, common cardinal vein, coeliaco‐mesenteric artery, gastero‐intestinal artery, and dorsal intestinal artery. Related smaller vessels were also determined.     

Temperature dependent activation of leucocyte populations of rainbow trout, Oncorhynchus mykiss, after intraperitoneal immunisation with Aeromonas salmonicida

The temperature dependence of in vivo activation of rainbow trout Oncorhynchus mykiss, leucocyte populations after intraperitoneal injection (i.p.) of fish with a T-cell independent antigen Aeromonas salmonicida (strain MT423) was investigated using a proliferation assay and flow cytometric analysis with mab specific for trout leucocyte surface markers. In trout kept at 15-17 degrees C a prominent activation of blood and spleen leucocytes was found. Also, drastic changes of the percentage of the leucocyte populations in blood and spleen occurred: the amount of monocytes in the blood increased between day 2 and day 7 post injection (p.i.), whereas in spleen the amount of monocytes stayed at a high level (approximately 35%) after a depression between day 4 and day 7 p.i. The percentage of B-lymphocytes was increased first in spleen and then in blood. The percentage of granulocytes in blood was elevated during the whole experiment compared to control fish. In trout kept at 10-12 degrees C only blood leucocytes showed a weak activation after i.p. injection of A. salmonicida, whereas spleen leucocytes showed nearly no reaction. Only the percentage of granulocytes in the blood (day 2-14 p.i.) and of monocytes in the spleen (day 2 and day 8 p.i.) was changed compared to phosphate buffered saline (PBS)-injected fish. However, the development of A. salmonicida specific antibodies was contrary to the cellular reaction. Whereas antibodies could first be detected after 16-18 days p.i. in both groups the amount of antibodies was significantly higher in sera of trout kept at 10-12 degrees C at day 22 and day 28 p.i. than in sera of trout kept at 15-17 degrees C. These results indicate stronger A. salmonicida induced activation of monocytes, granulocytes and B-lymphocytes at higher temperature. However, the development of a specific antibody response against A. salmonicida seemed to be more effective at lower temperatures.     

Effects of sampling on blood parameters in the rainbow trout, Salmo gairdneri Richardson

The effects of sampling and short-term storage of blood samples on the blood parameters of rainbow trout were evaluated by comparing values obtained from resting fish sampled via cannulae and from fish sampled by cardiac puncture. Sampling stress causes an increase in haematocrit value and a decrease in mean cellular haemoglobin concentration, indicating red cell swelling. These changes are aggravated by consecutive storage of samples. Also, blood ionic balance is affected. The K⁺ concentration of plasma increases and plasma Cl⁻ concentration decreases owing to sampling. During storage the plasma K⁺ concentration decreases far below resting levels in samples taken by cardiac puncture, whereas plasma Cl⁻ level returns to pre-stress levels. Owing to the sampling- and storage-induced changes in blood parameters, care must be taken to ensure that similar sampling procedure is employed throughout to allow reliable comparisons between groups to be made.     

Effect of stress on blood coagulation and haematology in rainbow trout (Salmo gairdneri)

The effect of short-term stress on blood clotting times, cell counts, haematocrits, and blood glucose levels was studied in a hatchery strain and wild type rainbow trout, Salmo gairdneri. Blood clotting times declined and thrombocyte counts, haematocrits, and blood glucose levels increased after stress in both strains of trout. The wild type of rainbow trout, however, required less time to recover from the stress than the hatchery strain of rainbow trout. The implications of a stress activated blood coagulation system in fish are discussed.     

Age- and weight-dependent susceptibility of rainbow trout Oncorhynchus mykiss to isolates of infectious haematopoietic necrosis virus (IHNV) of varying virulence

The virulence of 5 European and 1 North American isolate of infectious haematopoietic necrosis virus (IHNV) was compared by infecting female sibling rainbow trout ('Isle of Man' strain) of different weights and ages (2, 20 and 50 g). The fish were exposed to 10(4) TCID50 IHNV per ml of water by immersion, and the mortality was recorded for 28 d. Two new IHNV isolates from Germany were included in the investigation. One was isolated from European eels kept at 23 degrees C (+/- 2 degrees C) and the other was not detectable by immunofluorescence with commercially available monoclonal antibodies recognising the viral G protein. The results showed that IHNV isolates of high or low virulence persisted in rainbow trout of all ages/weights for 28 d, with the exception of fish over 15 g in the eel IHNV (DF [diagnostic fish] 13/98)-infected groups from which the virus could not be reisolated on Day 28. The smallest fish were most susceptible to an infection with any of the IHNV isolates. The lowest cumulative mortality (18%) was observed in fingerlings infected with the North American isolate HAG (obtained from Hagerman Valley), and the highest mortality (100%) in DF 04/99 infected fish. The DF 04/99 and O-13/95 viruses caused mortality in fish independent of their weight or age. The isolates FR-32/87 and I-4008 were virulent in fish up to a weight of 20 g and caused no mortality in larger fish. In the IHNV HAG- and DF 13/98 (eel)-infected rainbow trout, no signs of disease were observed in fish weighing between 15 and 50 g. An age/weight related susceptibility of rainbow trout was demonstrated under the defined conditions for all IHNV isolates tested.     

Detection of Yersinia ruckeri in rainbow trout blood by use of the polymerase chain reaction

We evaluated a polymerase chain reaction (PCR) method for detecting Yersinia ruckeri, the bacterial pathogen causing enteric redmouth disease (ERM), in blood of rainbow trout Oncorhynchus mykiss. Identification of the PCR product was confirmed by Southern blot hybridization with a 32P-labeled oligonucleotide probe matching a sequence within the small subunit ribosomal RNA gene of Y. ruckeri. Following a 1 h immersion of rainbow trout in water with 4.5 x 10(6) colony-forming units of Y. ruckeri l(-1), the PCR was positive for all blood samples from 1 h (first sample) to 5 d and was negative from 9 to 30 d (last sample). Fish in this experiment did not show signs of disease, probably because they had been vaccinated against Y. ruckeri. To test this method with naturally infected fish, 42 rainbow trout from hatcheries were examined. Four of these fish had clinical signs of ERM and were infected with Y. ruckeri based on bacteriological culture. The PCR method detected Y. ruckeri in blood, intestine, liver, and trunk kidney from the 4 fish with ERM and from 5 additional rainbow trout that were bacteriologically negative for Y. ruckeri. Three of 5 rainbow trout from streams receiving effluent from hatcheries were positive for Y. ruckeri when tested with PCR, although there was no growth of Y. ruckeri on culture plates inoculated with the same samples. Samples were successfully stored for 1 wk in lysis buffer at 25 degrees C. This study demonstrated that a non-lethal blood sample can be used with PCR to detect Y. ruckeri.     

Meristic variation among world hatchery stocks of rainbow trout,Salmo gairdneri Richardson

Synopsis Sixteen meristic characters were examined among 10 stocks of rainbow trout to establish their inter- and intrastock variability and relative discriminating power. The number of vertebrae, dorsal fin rays, scales above and below and lateral line, oblique scale rows and pectoral fin rays were found to be the most useful meristic characters in identifying stocks. Examination of the extent of meristic divergence among 10 hatchery or naturalized stocks from various regions of the world, using analysis of variance, the generalized distance function and per cent overlap, revealed that each stock exhibited highly significant differences in at least one meristic character, thereby demonstrating a high degree of intraspecific variability in meristic expression.In multivariate terms, stocks from Idaho and Alaska were almost totally divergent from all other stocks examined. Multivariate analysis of meristic features proves to be a useful method for identifying the extent of phenotypic variability among and within divergent stocks of rainbow trout. The observed meristic variability in test stocks of hatchery fish is seemingly genetically set within the limits previously described for native populations of rainbow trout.     

Influence of dietary composition on gluconeogenesis from L-(U-14C)glutamate in rainbow trout (Salmo gairdneri)

The effect of dietary composition (high-protein, high-carbohydrate and high-fat diets) and starvation on in totum gluconeogenesis from L-(U-14C)glutamate was studied in the rainbow trout. High-fat and high-carbohydrate diets produced a significant hyperglycaemia. Lower blood glucose values were obtained in trout fed on a high-protein diet. Liver glycogen levels were significantly lower in trout fed on carbohydrate-free diets (high-protein and high-fat diets) and in starved fish. Gluconeogenesis from L-(U-14C)glutamate was markedly reduced in fish given the high-carbohydrate diet and significantly enhanced in starved fish. Radioactive liver glycogen was higher in starved fish, although the amount of radioactivity incorporated into glycogen was very low.     

Avoidance response of two-year-old rainbow trout, Salmo gairdneri Richardson, to air-supersaturated water: hydrostatic compensation

Vertical swimming responses of 2-year-old rainbow trout were tested with air saturated and air supersaturated water in tank experiments. The level of supersaturation varied between 115 and 125% total gas pressure. Control groups offish were kept in tanks with saturated water. No consistent vertical avoidance response was observed in the fish tested, but the mortality of fish restricted to the upper 30 cm of the tanks was significantly greater than fish free to sound to the whole depth of the tanks. It is concluded that the Norwegian stock of rainbow trout do not avoid air-supersaturation at levels from 115 to 125% TGP by active hydrostatic pressure compensation. An incidental type of hydrostatic pressure compensation seemed to be taking place during these experiments, as indicated by different levels of mortality in tanks with different depths. This incidental type of hydrostatic compensation may explain the observed difference in tolerance to supersaturation between wild fish and fish kept in experimental tanks.     

Microsatellite DNA analysis of rainbow trout (Oncorhynchus mykiss) from western Alberta, Canada: native status and evolutionary distinctiveness of “Athabasca” rainbow trout

Molecular genetic assays can contribute to conservation of aquatic taxa by assessing evolutionary and taxonomic distinctiveness, levels of genetic variation within and between populations, and the degree of introgression with introduced taxa. The Athabasca River drainage of␣western Alberta, Canada is one of only three (and the largest) drainages flowing east of the continental divide that contain native populations of rainbow trout (Salmonidae: Oncorhynchus mykiss). The “Athabasca” rainbow trout has been considered a preglacial relict worthy of special conservation measures. In addition, the native range of Athabasca rainbow trout has seen many instances of introductions of non-native populations since the beginning of the 20th century. We assayed rainbow trout from the Athabasca River drainage, from hatchery populations, and from representative populations in adjacent regions (N = 49 localities) for variation at 10 microsatelite loci to assess the level of evolutionary distinctiveness of Athabasca rainbow trout, and to assess the levels of introgression with non-native hatchery fish. We found that native Athabasca rainbow trout did not form a distinctive genetic assemblage and that the greatest amount of allele frequency variation was attributable to contemporary drainage systems (29.3%) rather than by a Athabasca/non-Athabasca distinction (12.6%). We found that 78% of all fish were confidently assigned to a “wild” rather than a “hatchery” genetic grouping and that most of the inferred introgression with hatchery fish was restricted to a few localities (N = 6). Our results suggest that: (i)␣Athabasca River rainbow trout are likely postglacial immigrants from adjacent populations of the Fraser River, and (ii) that there is no evidence of widespread introgression of hatchery alleles into native Athabasca River drainage rainbow trout.     

Crowding causes prolonged leucopenia in salmonid fish, despite interrenal acclimation

Crowding for 3 weeks significantly reduced the coefficient of condition of both brown trout and rainbow trout. However, acclimation of the hypothalamic-pituitary-interrenal (HPI) axis, as assessed by changes in plasma cortisol levels, occurred within 6 days for brown trout and within 10 days for rainbow trout. Blood lactate levels were significantly reduced in the crowded fish of both species throughout the experiment. Sexual maturation of the male fish significantly elevated the number of circulating red blood cells in both species, reduced the lactate levels in brown trout and elevated cortisol levels in the rainbow trout. Despite the relatively rapid interrenal acclimation, the numbers of thrombocytes and lymphocytes in the blood of both species were significantly reduced during the period of crowding and it is concluded that changes in the composition of circulating blood cells are more reliable indicators of chronic crowding stress than are plasma cortisol levels. These findings are discussed in relation to the role of the HPI axis in suppressing the defence systems of salmonid fish during periods of chronic stress.     

Effects of fish size and ration level on the growth and food conversion efficiency of rainbow trout, Salmo gairdneri Richardson

The growth rates of rainbow trout, Salmo gairdneri , which ranged in size from 0.6 to 5.2 g and were provided rations of three different sizes, were measured during a 15-day study. The relative maintenance rations (food/gram of fish at zero growth rate) decreased with increases of fish size. Consequently when fish were kept at low ration levels the growth rates and gross efficiencies of food conversion of 'large' fish were greater than those of 'small' fish. However, as ration level increased, the effects of fish size grew at the same rates or slower than small fish. With increases of ration to the highest levels (9–12%/day) gross efficiency values for large fish began to decline while those for small fish continued to increase.