Rainbow Trout Fingerlings Research Articles

Determination of the Effects of Fislh vs Plant and Feather Meal-based Diets on the Growth and Health of Rainbow Trout

Rahnema, S. and Borton, R. 2007. Determination of the effects offish vs plant and feather meal-based diets on the growth and health of rainbow trout. J. Appl. Anim. Res., 32: 113–117. Two hundred and forty fingerling rainbow trout were used in an experiment to compare performance of rainbow trout receiving diets containing various levels offish meal (FM) and/or plant and feather meal protein (PFMP) based diets. Fish were fed once per day all the feed that they would eat within 15 minutes. Feed consumption and fish weights (by cage) were measured seven times over a 90-day period. At the end of the feeding trial, two fish from each cage were harvested, frozen in water and stored at −25C. After thawing one trout from each cage was wrapped in aluminum foil and baked in an oven at 163C for 30 min for organoleptic evaluation. The ash content as well as calcium, phosphorus, magnesium, potassium and sodium content of the diets declined as the amount of PFM was increased. Fish consuming a diet containing 67% PFMP consumed less feed (P<.02) than fish on FM or 33% PFMP diets with similar ADG. Also, fish on 100% PFMP consumed less feed (P<.02) than fish on either FM or 33% PFMP diets and gained less (P<.001) than the other three treatments. Feed-to-gain ratios showed a similar effect as the ADG. Taste panel analysis showed no significant differences (P>.413) for the various parameters tested. This study showed that PFMP can be substituted for 67% of fish meal with no adverse effect on the performance of rainbow trout.

Detection of naphthenic acids in fish exposed to commercial naphthenic acids and oil sands process-affected water

Naphthenic acids are a complex mixture of carboxylic acids that occur naturally in petroleum. During the extraction of bitumen from the oil sands in northeastern Alberta, Canada, naphthenic acids are released into the aqueous phase and these acids become the most toxic components in the process-affected water. Although previous studies have exposed fish to naphthenic acids or oil sands process-affected waters, there has been no analytical method to specifically detect naphthenic acids in fish. Here, we describe a qualitative method to specifically detect these acids. In 96-h static renewal tests, rainbow trout (Oncorhynchus mykiss) fingerlings were exposed to three different treatments: (1) fed pellets that contained commercial naphthenic acids (1.5mg g(-1) of food), (2) kept in tap water that contained commercial naphthenic acids (3mg l(-1)) and (3) kept in an oil sands process-affected water that contained 15mg naphthenic acids l(-1). Five-gram samples of fish were homogenized and extracted, then the mixture of free fatty acids and naphthenic acids was isolated from the extract using strong anion exchange chromatography. The mixture was derivatized and analyzed by gas chromatography-mass spectrometry. Reconstructed ion chromatograms (m/z=267) selectively detected naphthenic acids. These acids were present in each fish that was exposed to naphthenic acids, but absent in fish that were not exposed to naphthenic acids. The minimum detectable concentration was about 1microg naphthenic acids g(-1) of fish.

Evaluation of an Exposure Assay to Measure Uptake of Sediment Pah by Fish

The ecological risks of polynuclear aromatic hydrocarbons (PAH) in aquatic sediments will vary with both toxicity and bioavailability to aquatic biota. While there are standardized protocols to test the acute toxicity of sediment-borne compounds to aquatic invertebrates, there are none for assessing bioavailability to fish. We found that sediment-borne PAH caused an exposure-dependent induction of cytochrome P450 (CYP1A) enzymes in rainbow trout (Oncorhynchus mykiss) fingerlings exposed in semi-static 96 h bioassays, as shown by increased activity of ethoxyresorufin-o-deethylase (EROD). Assuming that PAH are taken up by trout due to partitioning from organic and inorganic constituents of sediments, we tested the effect of different test variables on bioaccumulation using induction as an index of exposure. EROD activity increased with exposure of fish to increasing volumes of sediments containing PAH, i.e., with increasing ratios of sediment to water. Uptake of single compounds from sandy sediments did not differ from uptake from clay or low organic (7% LOI - loss on ignition) sediments, but decreased when organic content was very high (58% LOI). Maximum induction was observed within 24 h of exposure and at 7.5 degrees C relative to 15, 22, or 28 degrees C. Storage and handling techniques had minor effects on sediment EROD induction potency. Absolute EROD activity was greater in white sucker (Catostomus commersoni) a benthic species, than in trout, a pelagic species. However, when basal (negative control) activity was accounted for, there was no difference in response between the species. Together, these experiments provide a basis for developing a standard protocol to test the bioavailability to fish of sediment-borne PAH.

Genotyping and Pathogenicity of Viral Hemorrhagic Septicemia Virus from Free-Living Turbot ( Psetta maxima ) in a Turkish Coastal Area of the Black Sea

Viral hemorrhagic septicemia (VHS) is one of the most serious fish viral diseases for cultured rainbow trout (Oncorhynchus mykiss), although VHS virus (VHSV) seems to be ubiquitous among marine fishes. In the present study, VHSV isolation was performed with free-living and cultured turbot (Psetta maxima) in the Trabzon coastal area of the Black Sea to evaluate participation of VHSV in mass mortalities of seed-produced turbot larvae. VHSV was detected in 14 of 66 free-living spawners (positive ratio, 21.2%), 1 of 65 free-living immature fish (1.5%) and 7 of 40 cultured brood stock (17.5%), respectively. Based on a partial glycoprotein gene nucleotide sequence, Turkish VHSV isolates were classified into the class I-e of genotype I and were the most closely related to the GE-1.2 isolate (>98% identity), which was found >20 years ago in Georgia. Thus, it was revealed that Turkish VHSV isolates were not introduced from European countries, it could be an indigenous type of VHSV distributing in the Black Sea environment. In pathogenicity tests, the Turkish isolates did not induce mortality in turbot larvae and rainbow trout fingerlings. Mass mortalities at a rate of approximately 90% occurred in turbot larvae produced by experimental seeding, although VHSV was not detected in any dead fish. Thus, it was concluded that mass mortality in the seed-produced turbot larvae was not caused by VHSV infection.

The Effects of Whirling Disease on Growth and Survival of Snake River Cutthroat and Colorado River Rainbow Trout Fingerlings

AbstractTwo sizes of fingerling Snake River cutthroat trout Oncorhynchus clarkii behnkei and Colorado River rainbow trout O. mykiss were raised at hatcheries testing negative for Myxobolus cerebralis and stocked into the Dolores and Cache la Poudre rivers from 1999 to 2001. Populations were resampled over a 2‐year period to determine which species and size combination had the highest growth and survival rates. Fish were tested for M. cerebralis via polymerase chain reaction and pepsin−trypsin digest analyses. Growth and survival rates between the species and size groups were not significantly different in either river. In the Dolores River, annual survival for both species and sizes of fish combined ranged from 0.063 to 0.12. In the Cache la Poudre River, survival for both sizes of rainbow trout was 0.004; survival for cutthroat trout ranged from 0.182 to 0.53. Larger fish had higher growth rates than smaller fish, and cutthroat trout had higher rates than similar sizes of rainbow trout. In both rivers, a higher percentage of the rainbow trout sample was infected than in the cutthroat trout sample. Rainbow trout also had a higher mean number of spores per head than cutthroat trout, and small rainbow trout had higher spore counts than large rainbow trout. Survival rates for cutthroat trout in the Cache la Poudre River were the highest of any of the groups, suggesting a difference that is biologically significant. Raising fingerlings to sizes greater than 100 mm can improve poststocking survival. If rainbow trout are stocked into contaminated waters, raising fingerlings to a larger size does not appear to improve growth or survival rates. Stocking rainbow trout in the spring could maximize growth rates but will expose fish to greater triactinomyxon densities, resulting in higher intensities of infection.

Mass-Marking Rainbow Trout and Brown Trout Fingerlings with Oxytetracycline

ABSTRACT We immersed fingerling rainbow trout (Oncorhynchus mykiss) and brown trout (Salmo trutta) in a 500-mg/L solution of oxytetracycline (OTC) for 6 h to determine marking efficacy. The technique marked 100% and 92% of rainbow trout and brown trout otoliths, respectively. In a blind test using known marked and unmarked otoliths, one reader correctly identified 99% of rainbow trout and 95% of brown trout otoliths as either marked or unmarked. Reading errors for rainbow trout (1 out of 78) and brown trout (8 out of 167) were of omission. Mortality of OTC-marked trout was less than 3.5% and statistically similar to control groups. Thirty-five thousand fingerling brown trout stocked into two Tennessee tail waters were treated on the hatchery truck with 500 mg/L OTC and all of the fish in a subsample (n = 95) that was held for 30 d were marked. When fish were recaptured up to 14 months post-stocking, OTC marks were subsequently detected on all brown trout otoliths known be treated (n = 23). We concluded that OTC immersion is an effective technique for mass marking fingerling rainbow trout and brown trout during short-term stocking evaluations.

Determination of the Effects of Fish vs Plant vs Meat Protein-based Diets on the Growth and Health of Rainbow Trout

Rahnema, S., Borton, R. and Shaw, E. 2005. Determination of the effects of fish vs plant vs meat protein-based diets on the growth and health of rainbow trout. J. Appl. Anim. Res., 27: 77–80. One hundred eight fingerling rainbow trout were used in an experiment to compare feed consumption, growth rate, gain-to-feed efficiency and live and carcass characteristics for rainbow trout receiving diets containing fish meal (FM), plant protein (PP), or feather meal and meat meal (FMMM), based diets. Six trout were housed in an 18″ × 18″ × 22″ cage (18 total cages) and nine of these cages (three per treatment) were placed in each of two 1000-gallon tanks. Fish were fed twice per day all the feed that they would eat within 30 min. Feed consumption and fish weights (by cage) were measured once every other week. At the end of the feeding trial, one fish from each cage was harvested, frozen in water and stored at −25C. The left half of each trout was excised, wrapped in aluminium foil and baked in an oven at 163C for 30 min. The trout were then divided into approximately 1.0 cm 3 cubes (about 20 g) and presented to the panel for evaluation of flavour, off flavour, tenderness, juiciness and overall acceptability of the meat. The right half of each trout was excised and used for laboratory analyses of moisture, fat, ash and protein content. The Ca content of the PP was lower than FM and FMMM diets. Fish consuming the PP diet had consumed less feed (P<0.00) and had a lower average daily gain (P<0.02) than the fish on FM or FMMM diets. Feed-to-gain ratios for PP and FM diets were similar and both were lower (P<0.00) than that of the FMMM diet. There were no differences due to treatment for moisture, fat, crude protein or ash content of the trout. Trout fed the FM diet were juicier and tenderer than the trout fed the PP diet. It is concluded that a meat scrap ration may substitute for the commercial fish meal ration if it is economically available.

Effect of Pseudomonas sp. MT5 baths on Flavobacterium columnare infection of rainbow trout and on microbial diversity on fish skin and gills

Use of Pseudomonas sp. strain MT5 to prevent and treat Flavobacterium columnare infection was studied in 2 experiments with fingerling rainbow trout Oncorhynchus mykiss. In the first experiment, length heterogeneity analysis of PCR-amplified DNA fragments (LH-PCR) was used to assess the effect of antagonistic baths on the microbial diversity of healthy and experimentally infected fish. In the 148 samples studied, no difference was found between bathed and unbathed fish, and 3 fragment lengths were detected most frequently: 500 (in 75.7% of the samples), 523 (62.2%) and 517 bp (40.5%). The species contributing to these fragment sizes were Pseudomonas sp., Rhodococcus sp. and F. columnare, respectively. A specific PCR for detection of Pseudomonas sp. MT5 was designed, but none of the tissue samples were found to be positive, most likely indicating poor adhesion of the strain during bathing. LH-PCR was found to be a more powerful tool for detecting F. columnare in fish tissue than traditional culture methods (chi2 = 3.9, df = 1, p < 0.05). Antagonistic baths had no effect on the outbreak of infection or on fish mortality. F. columnare was also detected in healthy fish prior to and after experimental infection, indicating that these fish were carriers of the disease. In the second experiment, intensive Pseudomonas sp. MT5 antagonistic baths were given daily to rainbow trout suffering from a natural columnaris infection. Again, the antagonistic bacteria had no effect on fish mortality, which reached 95 % in both control and antagonist-treated groups in 7 d.

Effect of conjugated linolenic acid (cis-9, trans-11, cis-13-18:3) on growth performance and lipid composition of fingerling rainbow trout Oncorhynchus mykiss

: This study investigated the effect of conjugated linolenic acid (CLNA) on the growth and lipid composition of fingerling rainbow trout Oncorhynchus mykiss. Thirty individuals in each tank with three dietary treatments and duplicate groups were subjected to three dietary levels (0:4, 2:2, 4:0) of CLNA and linolenic acid (LNA) at 16°C in the laboratory for a period of 9 weeks. Punicic acid (cis-9, trans-11, cis-13–18:3) and linseed oil were used as sources of CLNA and LNA, respectively. The hepatosomatic index and body lipid content of the 2% CLNA dietary treatment increased significantly (P < 0.05) with respect to the control (LNA treatment). But the specific growth rate and percent gain did not improve significantly. After 6 weeks’ observation, the 4% CLNA dietary treatment exhibited higher mortality and liver weight but lower weight gains (1.1–1.9 g). No significant differences were observed in the results of the feed efficiency and moisture as well as the protein content of the whole body among the treatments. Incorporation of CLNA into fish tissues was at a distinctly higher level in neutral lipids than in polar lipids. Increased levels of 22:6n-3 were found in the 4% CLNA treatment but decreased levels were found in the 2% CLNA treatment in both neutral and polar fractions. In the CLNA treatments, saturated fatty acid was relatively unaffected, the level of 18:1 was increased and the level of 18:2n-6 was decreased. These results indicate that the lower level (2%) of CLNA had no significant effect on the growth and the higher level (4%) of CLNA caused higher mortality as well as attenuating the growth of the fish. Dietary CLNA accumulated in a greater amount in the neutral lipids and modulated the fatty acid composition in the whole body of rainbow trout fingerlings.

Identification and molecular characterization of the rainbow trout calpains (Capn1 and Capn2): their expression in muscle wasting during starvation

Calpains are calcium regulated proteases involved in cellular functions that include muscle proteolysis both ante- and postmortem. Here, we describe the molecular characterization of the rainbow trout catalytic subunits of the μ- and m-calpains, respectively. The cDNA sequence for Capn1 encodes a protein of 704 amino acids with a calculated molecular mass of 79.9 kDa. The amino acid sequence shows 66% and 86% identity with the mouse and zebrafish Capn1, respectively. The Capn2 cDNA codes for a protein consisting of 701 amino acid residues with a calculated molecular mass of 78.2 kDa. The protein shows 65% amino acid sequence identity with the mouse and chicken Capn2. The two isozymes of rainbow trout have the characteristic domains: I (propeptide), II (cysteine catalytic site), III (electrostatic switch), and IV (contains five EF-hands). Because starvation induces muscle wasting, the hypothesis of this study was that starvation could affect regulation of the calpain system in muscle. Starvation of rainbow trout fingerlings (15–20 g) for 35 days stimulated the expression of Capn1 (2.2-fold increase, P<0.01), Capn2 (6.0-fold increase, P<0.01), and calpastatins (1.6-fold increase, P<0.05) as measured by quantitative real-time RT-PCR. The mRNA changes led to a 1.23-fold increase in the calpain catalytic activity. The results suggest a potential role of calpains in protein mobilization as a source of energy under fasting condition.

Effect of Stocking Density on Growth, Yield, and Costs of Producing Rainbow Trout, Oncorhynchus mykiss, in Cages

Rainbow trout, Oncorhynchus mykiss, were raised in culture cages (1 m3) to determine the effect of stocking density on growth, survival, and percentage of market-size fish. Large fingerling rainbow trout (20-25 cm, 232 g average weight) were stocked into six cages located in a 0.4-ha pond. Two stocking densities (100 or 200 fish/cage) were used, and fish were grown for 140 days (2000-April 2001). Average total harvest weight (35.0 kg) in the low-density cages was approximately one-half the average total harvest weight (61.2 kg) in the high-density cages. Average weight gain (11.7 kg to 15.1 kg) and feed conversion (1.2 to 1.5) were also smaller for the low-density cages. Average survival was 96.7% for the low-density cages and 94.2% for the high-density cages, with the percentage of market-size fish (< 29 cm) averaging 50.3% and 52.0%, respectively. Production costs for the actual experiment and the revenues from fish sold at the end of the study were collected. An enterprise budget based on the experimental results for the two densities was developed to determine if a culture operation of this size would produce a net return. Production costs and revenues from the experiment resulted in a large negative return (-$3,124) and high breakeven price ($13.53/kg).

Dietary Uptake of Polychlorinated Biphenyls (PCBs) by Rainbow Trout

AbstractThe presence of detectable levels of polychlorinated biphenyls (PCBs) in commercially produced fish feed has raised a concern about the degree of biomagnification of these contaminants in hatchery‐reared trout. Our objectives were to (1) define the relationship between concentrations of PCBs in fish feed and in fish tissue and (2) estimate the relative contributions of feed and hatchery supply water to PCB concentrations in fish. We conducted a 6‐month feeding trial with fingerling rainbow trout Oncorhynchus mykiss fed commercial diets with four concentrations of PCBs: a low‐PCB diet (69 ng/g); a typical commercial diet (126 ng/g); and the typical diet spiked with PCBs at two levels (220 and 280 ng/g). The concentrations of PCBs in fillets after 1 month were commensurate with those in the feeds and remained relatively stable for the next 5 months; mean PCB concentrations in fillets ranged from 54 to 94 ng/g. Low levels of PCBs were detected in the hatchery supply water. We used the concentrations of PCBs in the feeds, absorption rates of PCBs, and two different rates of PCB depuration to estimate the potential uptake of PCBs from supply water. When we used a low depuration rate (half‐life = 219 d), the computed body burdens of PCBs could be entirely attributed to the feeds. When a high depuration rate (half‐life = 66 d) was used, some uptake of PCBs from the supply water was likely, but most of the total body burden originated from the feeds. We concluded that rainbow trout fed a diet with 126 ng/g PCBs would have a PCB concentration of about 60 ng/g in their fillets, which is high enough to warrant issuance of a consumption advisory (no more than one meal of fish per week) under a protocol adopted by some Great Lakes states.

Antagonistic effects of branched-chain amino acids induced by excess protein-bound leucine in diets for rainbow trout ( Oncorhynchus mykiss)

Three feeding experiments were conducted to evaluate the antagonistic effects induced by excess leucine (Leu), derived from intact protein (zein or corn gluten meal (CGM)), on growth and protein utilization of fingerling rainbow trout ( Oncorhynchus mykiss). In Experiment 1, three semipurified diets containing wheat gluten+limiting essential amino acids (EAA), zein+EAA, or zein+EAA+isoleucine (Ile)+valine (Val), were fed for 6 weeks by self-feeders. In Experiment 2, the three diets used in Experiment 1 and a zein diet with EAA and levels of Ile and Val enrichment at one half the amounts used in Experiment 1 were fed by hand for 6 weeks. In Experiment 3, a fish meal diet and three non-fish meal diets containing 23.5% CGM supplemented either with non-essential amino acids, EAA, or EAA+Ile+Val, were fed by hand for 60 days. In Experiment 1, growth and N retention of fish fed the zein diets, regardless of the Ile and Val enrichment, were inferior ( P<0.05) to fish fed the wheat gluten diet due largely to reduced feed intake. In Experiment 2, fish fed zein diets with both levels of Ile and Val enrichment attained growth and N retention not significantly different ( P>0.05) from those of fish fed the wheat gluten diet. In Experiment 3, fish fed the two non-fish meal diets with EAA supplementation, regardless of the Ile and Val enrichment, showed identical growth and protein utilization to those of fish fed the fish meal diet. Free Ile and Val concentrations in the plasma, liver and muscle of fish fed the zein and CGM diet without Ile and Val enrichment were lower than those of fish fed the wheat gluten diet and fish meal diet, respectively, whereas the Ile and Val enrichment restored the concentrations. These results suggest that antagonisms induced by excess Leu from zein occur in rainbow trout. A practical level of CGM inclusion had no adverse effect on growth performance in a 60-day feeding, however, certain antagonisms appear in tissue branched-chain amino acid (BCAA) concentrations.

Simulated Thermal Tempering versus Sudden Temperature Change and Short-Term Survival of Fingerling Rainbow Trout

We examined the effects of thermal shock on poststocking survival of fingerling rainbow trout Oncorhynchus mykiss (mean total length, 99 mm; mean weight, 10 g), some of which were thermally tempered at stocking and others not. In one experiment we assessed survival when fish experienced increases in water temperature from 8°C to 24°C at two tempering rates (4°C/h and 8°C/h) and by an immediate transfer. In a second experiment we assessed survival when water temperatures were cooled to 0.3°C for 2 h and fish were subsequently transferred into 8°C and 24°C water without tempering. Both experiments were conducted with controls at 8°C that were subjected to the same handling procedures without any changes in water temperature. Fingerling rainbow trout were found to be very tolerant of all treatments, with few or no mortalities during the treatments or during the 2 weeks following treatment. Our experiments suggest that rapid changes to high but sublethal temperatures will not directly cause high mortalities of fingerling rainbow trout stocked into waters for sport fisheries, but short-term behavior anomalies or other stressors may affect poststocking survival in the wild.

Virulence stability in Flavobacterium psychrophilum after storage and preservation according to different procedures.

Experimental infections and lethal dose 50% (LD 50) evaluation were conducted in rainbow trout fingerlings, using a virulent strain of Flavobacterium psychrophilum processed and stored or maintained in different ways; lyophilisation, freezing at -80 degrees C, maintenance in enriched Anacker and Ordal (EAO) medium at 4 degrees C, revival and subsequent in vivo passages in fish. Experiments were performed 1, 8 and 23 months after storing the bacteria. Out of a total of 12 cultures revived for experimentation, one failed to grow and another was found to express modified properties including decreased virulence in spite of in vivo passages. In all other cases, whatever the conditions of preservation, virulence was fairly well maintained after 1 and 8 months of storage. In the last test, after 23 months, the bacteria maintained in the EAO medium at 4 degrees C were found significantly attenuated. Conversely, lyophilised and frozen bacteria only expressed a slight increase in LD0. It was concluded that virulent strains of F. psychrophilum were likely to retain their properties without special provisions within limited periods of time, and that both lyophilisation and freezing at -80 degrees C were reliable methods for long-term preservation of virulence.

Bioavailability to juvenile rainbow trout (Oncorynchus mykiss) of retene and other mixed‐function oxygenase‐active compounds from sediments

Retene (7-isopropyl-1-methylphenanthrene) is a naturally formed polycyclic aromatic hydrocarbon (PAH) that causes teratogenicity in fish larvae and induction of cytochrome P450 (CYP1A) enzymes. Retene occurs at high concentrations (< or =3,300 microg/g dry wt) in surface sediments contaminated by resin acids from pulp mill effluents. To assess the environmental risks of retene, it is important to evaluate conditions affecting its bioavailability and accumulation by fish. Fingerling rainbow trout were exposed to retene-spiked or naturally contaminated sediments and sampled after 4 d to determine liver CYP1A activity and concentrations of retene metabolites in bile as indicators of retene accumulation. Industrially contaminated sediments collected near a bleached kraft pulp and paper mill discharging to Lake Saimaa, Finland, significantly induced trout liver CYP1A activity, indicating accumulation of arylhydrocarbon receptor (AhR)-active ligands. Bile of these fish contained retene metabolites, providing direct evidence that retene is bioavailable, presumably via desorption from sediments. Induction of CYP1A in fish exposed to sediments spiked with retene or benzo[k]fluoranthene supported this conclusion. While the extent of CYP1A induction by spiked sediments declined after storage (i.e., aging), a portion of the spiked PAHs remained bioavailable. However, retene was not the sole CYP1A inducer in industrially contaminated sediments, as shown by induction in fish injected with sediment extracts oxidized to remove labile PAHs but not persistent organochlorine compounds such as chlorinated dioxins and furans.

Bioavailability of amino acid-chelated and glass-embedded manganese to rainbow trout, Oncorhynchus mykiss (Walbaum), fingerlings

Feeding experiments were conducted to determine the bioavailability of new types of manganese (Mn) supplement to rainbow trout fingerlings. Two levels of Mn (7 and 14 mg kg−1 diet) were supplemented to diets using either manganese sulphate (Mn-S), glass-embedded Mn (Mn-Gl), or amino acid-chelated Mn (Mn-Am); more than one acid was used to chelate the metal. Rainbow trout weighing 1.30 g on average were fed the experimental diets for 12 weeks. Absorption of Mn from various compounds was evaluated using larger fish (105 g on average) fed the experimental diets. Growth was higher in the group supplemented with Mn-Am at both levels. Whole-body Mn content in fish fed the diet supplemented with Mn-Am was significantly higher than the other sources. Bone Mn accumulation was significantly higher in treatments with 14 mg Mn kg−1 diet from all sources, except Mn-Gl. At 7 mg kg−1, absorption from Mn-Am was significantly higher than from Mn-Gl and Mn-S. Mn retention from both levels of Mn-Am supplementation was significantly higher (P < 0.05) than the rest. The results indicated that amino acid-chelated Mn provided more bioavailable nutrient than Mn-S and Mn-Gl. Further, availability of Mn from Mn-Gl is equivalent to that of Mn-S.

Immunity induced shortly after DNA vaccination of rainbow trout against rhabdoviruses protects against heterologous virus but not against bacterial pathogens

It was recently reported that DNA vaccination of rainbow trout fingerlings against viral hemorrhagic septicaemia virus (VHSV) induced protection within 8 days after intramuscular injection of plasmid DNA. In order to analyse the specificity of this early immunity, fish were vaccinated with plasmid DNA encoding the VHSV or the infectious haematopoietic necrosis virus (IHNV) glycoprotein genes and later challenged with homologous or heterologous pathogens. Challenge experiments revealed that immunity established shortly after vaccination was cross-protective between the two viral pathogens whereas no increased survival was found upon challenge with bacterial pathogens. Within two months after vaccination, the cross-protection disappeared while the specific immunity to homologous virus remained high. The early immunity induced by the DNA vaccines thus appeared to involve short-lived non-specific anti-viral defence mechanisms.

Creatine supplementation affects sprint endurance in juvenile rainbow trout

Fingerling rainbow trout were supplemented with equal amounts of creatine (Cr) by two routes: dietary (12.5 mg Cr per g food); or intraperitoneal injection (0.5 mg Cr per g fish). Endurance in a fixed velocity sprint test (at a speed of 7 BL s −1), and resting levels of white muscle metabolites (total creatine [a measure of free creatine plus phosphocreatine (PCr), ATP, lactate and glycogen] were assessed following 7 days of supplementation and compared to controls. None of the treatments had a significant effect on growth, muscle total creatine, percent phosphorylation of creatine, ATP or lactate. However, resting muscle glycogen was elevated in creatine-supplemented fish. Higher muscle glycogen corresponded to significantly greater endurance in creatine-supplemented fish. Although fish do not actively transport additional creatine into the muscle, a mechanism whereby circulating creatine acts to enhance muscle glycogen is present. These results suggest that the improved endurance may be due to an insulin-dependent mechanism (similar to that elucidated in mammalian studies) that allows fish to supercompensate muscle glycogen stores, thus extending endurance through enhanced glycolytic flux.

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.