Communications: Validation of a Solid-Phase Enzyme Immunoassay Technique for the Measure of Plasma Cortisol in Rainbow Trout

Abstract

A kit for a solid-phase enzyme immunoassay (SOPHEIA®) of cortisol in human sera was evaluated and validated for measuring cortisol in plasma of rainbow trout Oncorhynchus mykiss. The accuracy of the SOPHEIA was demonstrated by the recovery of exogenous cortisol concentrations of 25, 50, 100, and 250 ng/mL in charcoal-stripped fish plasma. The amounts (mean ± SE) recovered from triplicate samples were 29.9 ± 2.75, 47.5 ± 3.41, 101.7 ± 12.08, and 232.0 ± 11.06 ng/mL, respectively. The intra- and interassay coefficient of variation (CV = 100 × SD/mean) for cortisol levels in undisturbed fish (26.6 ± 1.18 ng/mL) were 14 and 10%, respectively. The intra- and interassay CV for elevated cortisol levels in stressed fish (330.8 ± 19.90 ng/mL) were 8 and 13%, respectively. Cross-reactivity determined for nine steroids in teleostean fish was negligible. Cortisol concentrations in serial dilutions of pooled fish plasma were parallel to the standard curve. Sensitivity (minimum detection limit) was 3.04 ng/mL. The SOPHEIA compared favorably to radioimmunoassay measurements of cortisol (r = 0.98; P < 0.001).     

The dose–response relation for the antinociceptive effect of morphine in a fish,rainbow trout

Jones, S. G., Kamunde, C., Lemke, K., Stevens, E. D. The dose–response relation for the antinociceptive effect of morphine in a fish, rainbow trout. J. vet. Pharmacol. Therap.  35 , 563–570. There have been suggestions that analgesics be used by fish researchers. But in the absence of dose–response data for morphine, this suggestion seems imprudent. The purpose of the present study was to develop a dose–response relationship in fish using six doses of morphine. The response (movement of the fins or tail) to a noxious stimulus (electrical shock to the face region) was monitored before and after a dose of morphine intraperitoneally (i.p.). The i.p. dose of morphine ED₅₀ in rainbow trout was 6.7 ± 0.8 mg/kg (n = 12 at each dose). The plasma morphine concentration EC₅₀ was 4.1 ± 1.5 mg/L. In a second experiment, rainbow trout tested with equal amounts of morphine and naloxone (30 mg/kg) showed that the antinociceptive effect of morphine was blocked by naloxone. It has been suggested that stress‐induced analgesia has been a confounding factor in some fish studies. However, plasma cortisol levels in our study indicated that stress was not a confounding factor in the present experiments. The ED₅₀ for morphine in fish was higher than that reported for humans or other mammals. Our observation showing a dose–response relation for morphine using a noxious stimulus supports arguments for its effectiveness as an antinociceptive drug in fish.     

The Effects of Myxobolus cerebralis on the Physiological Performance of Whirling Disease Resistant and Susceptible Strains of Rainbow Trout

Abstract

The development of rainbow trout Oncorhynchus mykiss strains that are resistant to whirling disease has shown promise as a management tool for populations in areas where Myxobolus cerebralis is present. However, the physiological effects of the disease on characteristics necessary for fish survival in natural river conditions have not been tested in many of these strains. Five rainbow trout strains were evaluated for their swimming ability and growth characteristics in relation to M. cerebralis exposure: the resistant German rainbow trout (GR) strain (Hofer strain), the susceptible Colorado River rainbow trout (CRR) strain, and three intermediate (hybrid) strains (F₁ = GR × CRR; F₂ = F₁ × F₁; B₂ = backcross of F₁ × CRR). Three broad response patterns among strain and exposure were evident in our study. First, exposure metrics, growth performance, and swimming ability differed among strains. Second, exposure to the parasite did not necessarily produce differences in growth or swimming ability. Exposure to M. cerebralis did not affect batch weight for any strain, and critical swimming velocity did not differ between exposed and unexposed families. Third, although exposure did not necessarily affect growth or swimming ability, individuals that exhibited clinical deformities did show reduced growth and swimming performance; fish with clinical deformities were significantly smaller and had lower critical swimming velocities than exposed fish without clinical deformities. Research and management have focused on GR × CRR hybrid strains; however, given the performance of the GR strain in our study, it should not be discounted as a potential broodstock. Additional field trials comparing the GR and F₁ strains should be conducted before wholesale adoption of the GR strain to reestablish rainbow trout populations in Colorado.

Received September 9, 2010; accepted May 27, 2011     

Wound Healing in Rainbow Trout following Surgical Site Preparation with a Povidone–Iodine Antiseptic

Abstract

We investigated the effects of preparing surgical incision sites with a topical antiseptic on wound healing and hematological response in rainbow trout Oncorhynchus mykiss. A povidone–iodine solution was applied both pre- and postsurgery to the incision sites on treated fish. Three-centimeter incisions in both treated (N = 9) and control (nontreated, N = 9) fish were closed with four nonabsorbable sutures sewn in a simple interrupted pattern. During the 42-d period of wound healing, there were no statistically significant changes in total erythrocyte counts (1.28 × 10⁶/mm³ ± 0.05 SE), in percentage of dividing erythrocytes (0.76% ± 0.07 SE), or in differential leukocyte counts. Postmortem, pathogenic bacterial infections in the kidney or spleen were not detected in any of the fish. There was no histological difference between control and treated incisions to show either beneficial or adverse tissue reactions to the topical antiseptic treatments. Blinded histological analysis revealed both treated and untreated incision sites healed within 42 d at the same rate. Therefore, preparation of the incision sites with a povidone–iodine antiseptic did not improve wound healing nor alter healing rate in rainbow trout under the conditions of this study.     

Assessment of serum protein fractions in rainbow trout using automated electrophoresis and densitometry

Background: Although rainbow trout (Oncorhynchus mykiss, Walbaum) are one of the most‐studied fish, electrophoretic techniques and classification of serum protein fractions have not been standardized, such that clinically useful values are lacking. Objective: The aim of the present study was to evaluate preliminarily the serum protein fractions of rainbow trout using automated cellulose acetate electrophoresis and densitometry. Methods: Serum samples from 25 rainbow trout (Oncorhynchus mykiss, Walbaum) were electrophoresed on cellulose acetate plates and quantified using densitometry. Results: A maximum of 6 fractions were identified and numbered, in order of decreasing mobility, as I, II, III, IV, V, and VI. In 3 of 25 (12%) samples, 6 fractions were identified; in 18 (72%) samples, 5 fractions were identified; and in 4 (16%) samples, 4 fractions were identified. Fractions I, V, and VI were always clearly identifiable, whereas fractions II and IV were frequently fused and indistinguishable from fraction III. The pattern with 5 fractions was the most probable type (χ², P<.01). The mean (±SEM) protein concentrations of the 6 fractions were I, 0.8±0.1 g/dL; II, 0.3±0.0 g/dL; III, 1.6±0.1 g/dL; IV, 0.3±0.1 g/dL; V, 0.6±0.0 g/dL; and VI, 0.2±0.0 g/dL. Based on comparison of serum and plasma electrophoretic patterns from 8 fish, fibrinogen was found in fraction V. Conclusion: Automated cellulose acetate electrophoresis and densitometry appear to be a practical method for estimation of serum protein fractions in rainbow trout.     

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

Abstract

Two 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.     

Early Life Stage Survival and Susceptibility of Brook Trout,Coho Salmon,Rainbow Trout,and Their Reciprocal Hybrids to Infectious Hematopoietic Necrosis Virus

Abstract

Triploid (heat-shocked) and diploid groups of rainbow trout Oncorhynchus mykiss, brook trout Salvelinus fontinalis, coho salmon Oncorhynchus kisutch, and reciprocal hybrids were produced, monitored for early life stage survival, and evaluated for susceptibility to infectious hematopoietic necrosis virus (IHNV). The female rainbow trout × male brook trout triploid hybrids had significantly greater (P < 0.01) survival than the diploid hybrids of this cross. The heat-shocked hybrid group of the female rainbow trout × male coho salmon also exhibited significantly greater survival to the eyed egg stage of development than the untreated group of this hybrid. Studies of the susceptibility of treatment groups to a 1990 IHNV isolate from the Hagerman Valley were conducted by using a standardized immersion exposure procedure at one or two different mean body weights. The diploid brook trout and coho salmon and two triploid hybrids (female rainbow trout × male brook trout or male coho salmon) were significantly less (P < 0.05) susceptible to IHNV than the pure-species diploid and triploid rainbow trout groups.     

Effects of Hyperoxic Rearing Water on Blood Hemoglobin and Hematocrit Levels of Rainbow Trout

Abstract

Rainbow trout Oncorhynchus mykiss cultured under hatchery conditions were exposed to hyperoxia by injection of oxygen into the rearing water. In two separate studies of 67 and 73 d, mean hemoglobin of experimental fish reared at oxygen levels averaging 147–220% saturation was 7.8–8.7% lower than that of control fish reared at mean oxygen saturations of 66–74%. Mean hematocrit of experimental fish was also 3.1–5.7% lower than that of control fish. Fish reared in hyperoxic conditions did not differ in growth, survival, or behavior from control fish. Fish exposed to hyperoxia rapidly adjusted hemoglobin and hematocrit to levels similar to those of control fish after oxygen injection was stopped.     

Effects of Ergosan on the expression of cytokine genes in the liver of juvenile rainbow trout (Oncorhynchus mykiss) exposed to enteric red mouth vaccine

The effects of administration of the immunomodulator Ergosan, an algal extract containing alginic acid, in juvenile rainbow trout (Oncorhynchus mykiss) exposed to AquaVac vaccination, were tested. Juveniles treated with Ergosan, 95 days after the beginning of first solid feeding and control fish fed solely on commercial diet, were vaccinated by immersion in AquaVac solution. The time-course of the effects of vaccination on liver immunorelated gene modulation and on the tolerance to stress manipulation connected with the vaccination was investigated. Liver and plasma sampling was performed at the following times: T=pre-vaccination, T0=5min, T1=2h, T2=8h, T3=24h, T4=48h and T5=72h post-vaccination. Interleukin-1beta (IL-1beta), interleukin-8 (IL-8), tumor necrosis factor alpha 2 (TNF alpha 2) and heat shock protein 70 (Hsp70) gene expression in trout liver was monitored by real-time PCR using Acidic Ribosomal Phosphoprotein P0 (ARP) as internal standard. The evaluation of the plasma cortisol levels was performed by EIA. In AquaVac-vaccinated fish, both the gene expression of Hsp70 and the plasma cortisol levels during the time-course were significantly (P<0.05) lower in Ergosan-treated fish with respect to control, indicating the positive role of Ergosan on handling stress tolerance. This study also demonstrated the stimulatory properties of Ergosan on cytokine genes expression involved in innate immune response: liver IL-1beta, IL-8 and TNF alpha 2 gene expression was significantly (P<0.05) higher in trout fed on Ergosan compared to control, indicating a positive role of this feed additive in improving the immune responsiveness to AquaVac vaccine.     

单色光对肉鸡免疫功能的影响

选用260只刚出壳AA肉鸡公雏,随机分为红（660 nm）、绿（560 nm）、蓝（480 nm）和白（400-700 nm）4个光色处理组,分别用4种发光二级管作为光源进行处理。每个处理设5个重复,每个重复13只鸡,人工光照光强度均为15 lx,光照时间为23 h,试验期为7周。49日龄测定肉鸡脾脏的质量,21和49日龄测定外周血T淋巴细胞转化率和血清皮质醇水平,14、28、42和49日龄测定新城疫（NDV）抗体滴度。结果表明：与红光组比较,蓝光组49日龄肉鸡脾脏的质量提高42.2%（P〈0.05）,而白光、绿光和蓝光各组间差异不显著（P〉0.05）。与白光组相比,蓝光组21和49日龄皮质醇水平分别降低25.2%和26.2%（P〈0.05）。与红光组比较,28日龄时绿光组的新城疫抗体水平显著高32.9%（P〈0.05）,而白光、红光和蓝光各组间差异不显著（P〉0.05）;49日龄时蓝光组NDV的抗体水平显著高62.8%（P〈0.05）,但蓝光、绿光和白光组间差异不显著（P〉0.05）。与红光组比较,21日龄时白光和绿光组肉鸡外周血T淋巴细胞的转化率均显著提高（分别为107.1%和80.8%,P〈0.05）,49日龄时白光和蓝光组分别显著提高41.5%和26.9%（P〈0.05）。上述结果表明,在15 lx光强度下,肉鸡生长前期选用绿光照明,后期改为蓝光照明,可以提高肉鸡免疫功能,而且在一定程度上蓝光还有缓解免疫应激的作用。     

Comparison of Hatchery and Field Performance between a Whirling-Disease-Resistant Strain and the Ten Sleep Strain of Rainbow Trout

Abstract

A whirling-disease-resistant strain of rainbow trout Oncorhynchus mykiss (GRHL strain) derived from a backcross of an F1 hybrid of two strains (German strain × Harrison Lake strain) with German strain females, was compared with the Ten Sleep (TS) strain of rainbow trout. The GRHL strain had consistently superior growth and feed conversion in two consecutive hatchery trials. Hatching and mortality rates were similar between strains. Both strains were stocked into two Utah reservoirs (Hyrum, Porcupine), and a third, Causey Reservoir, was monitored as a control for seasonal variation in prevalence of Myxobolus cerebralis. A total of 1,323 salmonids captured by gill net in spring and fall sampling between 2006 and 2008 were tested for M. cerebralis via pepsin-trypsin digest methods. Only eight of these (<1% per species) had clinical signs consistent with whirling disease. In both reservoirs, GRHL survived better than the TS and had higher growth rates. The prevalence of M. cerebralis was significantly lower for GRHL (18.1%) than TS (50.0%) in Porcupine Reservoir. In Hyrum Reservoir the trend was similar, but prevalence was lower and did not significantly differ between GRHL (9.6%) and TS (23.1%). For infected fish, no significant differences were observed between strains in myxospore counts in either Hyrum (GRHL = 911–28,244 spores/fish [spf], TS = 1,822–155,800 spf) or Porcupine (GRHL = 333–426,667spf, TS = 333–230,511 spf) reservoirs. Unmarked rainbow trout in both reservoirs had significantly higher myxospore counts than stocked fish of either strain. There were significant differences in M. cerebralis prevalence and myxospore loads among other naturally reproducing salmonids in the reservoirs. The trend in susceptibility was cutthroat trout Oncorhynchus clarkii > kokanee Oncorhynchus nerka > brown trout Salmo trutta. The GRHL performed well in both hatchery and field settings and is recommended for stocking programs.

Received December 28, 2011; accepted February 2, 2012     

Coat and hair color: hair cortisol and serotonin levels in lactating Holstein cows under heat stress conditions

The deleterious effects of heat stress on animal health are being increasingly recognized. This study aimed to determine hair cortisol (HC) and serotonin levels in lactating Holstein cows under heat stress conditions with different coat and hair‐cut color. Forty‐five multiparous lactating Holstein cows (days in milk = 130 ± 47, body weight = 753 ± 85 kg) were divided to two main groups of over 80% black coat color (BC) and over 85% white coat color (WC) visually observed based on registry certificates and subdividing to black hair sample (BH) and white hair samples (WH) in 2 × 2 factorial arrangements. Hair samples were taken from the forehead of the individuals. Higher HC levels were observed in BC than WC cows (P < 0.05). No differences were found in HC levels between BH and WH groups (P > 0.05). Serotonin levels showed no difference between BC and WC (P > 0.05). Interaction between coat color and hair color was not significant (P > 0.05). The cortisol levels in hair are not affected by pigmentation. However, pigmentation within the coat alters cortisol levels. In conclusion, white coat color retains less cortisol than the black coat. Therefore, white coats are preferable for dairy cows under heat stress conditions.     

Oxytetracycline Pharmacokinetics in Rainbow Trout during and after an Orally Administered Medicated Feed Regimen

Abstract

The pharmacokinetic–pharmacodynamic predictor of antimicrobial activity for tetracyclines is reported to be the area under the concentration–time curve at steady state (AUC_ss) divided by the minimal inhibitory concentration of the targeted pathogen. Here, we estimate AUC_ss values for oxytetracycline (OTC) in serum of rainbow trout Oncorhynchus mykiss by using a destructive sampling study design. Seventy-two rainbow trout were fed OTC-medicated feed at 74.7 ± 1.5 mg/kg (mean ± SD) body weight (BW) by oral gavage for 10 consecutive days. Serum was collected from nine fish at 1, 3, 6, 8, 10, 12, 15, and 22 d after dosing began. Serum OTC concentrations were measured by high-performance liquid chromatography with a 0.01-μg/mL limit of detection. The average OTC AUC_ss was 29.2 μg × h/mL and was estimated using nonlinear mixed-effects modeling and bootstrap resampling techniques. The elimination half-life was estimated as 85.0 h, and the fraction of steady state achieved was estimated as 0.85. The calculated AUC_ss (24.8 μg × h/mL) following 10 d of oral dosing with 75 mg OTC/kg BW was less than the estimated AUC_ss. Results suggest that the pharmacokinetics of OTC exposure, including the AUC_ss, is better evaluated by using multiday dosimetry than by using a standard single-dose protocol.

Received September 29, 2011; accepted January 30, 2012     

Establishment and Characterization of Seven Continuous Cell Lines from Freshwater Fish

Abstract

Seven continuous cell lines were established from salmonid and nonsalmonid fishes. Salmonid cell lines derived from rainbow trout Oncorhynchus mykiss and chum salmon O. keta were designated RTE and RTE-2 (rainbow trout embryo), RTT (rainbow trout tail), and SEH (“sake” or chum salmon embryo head). Nonsalmonid cell lines derived from pond smelt Hypomesus olidus, chevron snakehead Channa striata, and goldfish Carassius auratus were designated WF-1 (“wakasagi” fin), SHH (snakehead heart), and EPG (epithelioma papulosum of goldfish), respectively. Optimum growth for most of the cell lines was observed in Eagle's minimum essential medium buffered with sodium bicarbonate (26 mM) or a combination of sodium bicarbonate (8.9 mM) and tris (16 mM). Likewise, most of the cell lines showed optimum growth at the lowest NaCl concentration tested (0.116 M). Optimum growth temperatures ranged from 15 to 20°C for the salmonid cell lines and from 15 to 30°C for nonsalmonid cell lines. Except for RTT, the cell lines were heteroploid. Eleven fish viruses were used to test the susceptibility of these cell lines. Cell lines derived from salmonids developed cytopathic effects (CPE) when infected with 10 of the 11 fish viruses tested, except for RTT, which produced CPE with only 8 of the fish viruses. Six fish rhabdoviruses used in this study elicited a pronounced CPE when inoculated into nonsalmonid cell lines EPG, WF-1, and SHH. Among the new cell lines, RTE-2 showed the best potential for the isolation of fish viruses.     

Effects of Salinity on Yersinia ruckeri Infection of Rainbow Trout and Brown Trout

Abstract

Juvenile rainbow trout Oncorhynchus mykiss and brown trout Salmo trutta acclimated to freshwater or salinities of 9.0‰ or less were exposed to Yersinia ruckeri, the bacterial pathogen that causes enteric redmouth disease (ERM). Both species of fish were kept in the same recirculating systems after bacterial exposure. Rainbow trout mortality was significantly (P < 0.05) different in each salinity: 96.5% in freshwater, 89.5% in water of 1.1‰ salinity, 81.3% in 3.0‰ salinity, and 75.0% in 9.0‰ salinity (model SE = 1.0). All deaths occurred between 3 and 12 d after exposure to Y. ruckeri. Only 2.3% of brown trout in all salinities died, and differences among treatments were not significant. For both fish species, Y. ruckeri was isolated from liver, spleen, and trunk kidney of fish dying during this experiment, and lesions of rainbow trout were consistent with ERM. Yersinia ruckeri was not isolated from brown trout surviving for 21 d after bacterial exposure but was isolated from 3 of 24 surviving rainbow trout; a polymerase chain reaction assay detected the DNA of Y. ruckeri in 3 additional rainbow trout survivors. Neither the lesions of fish with ERM nor the percentage of surviving fish subclinically infected with Y. ruckeri was affected by salinity. Bacterial growth in vitro was not affected by low (≤9.0‰) salinity; however, bacterial adhesion to polystyrene was significantly reduced as salinity increased. Although mortality caused by Y. ruckeri was significantly lower for rainbow trout in water with slightly increased salinity, none of the salinities tested was effective in preventing serious losses caused by this pathogen in recirculating systems.     

Amending reduced fish‐meal feeds with marine lecithin,but not soy lecithin,improves the growth of juvenile cobia and may attenuate heightened responses to stress challenge

Sparing of marine resources in aquafeeds can be environmentally and economically advantageous; however, fish meal (FM) replacement can affect the production performance and physiological competence. Phospholipids are increasingly understood to be involved in maintaining growth and vigour in fish and may be deficient in reduced FM formulations. Accordingly, we evaluated the growth and stress tolerance of juvenile cobia fed typical (50% FM) or reduced FM feeds (12% FM) with or without phospholipid amendment [1% marine lecithin (12% FM + Marine PL) or soy lecithin (12% FM + Soy PL)] for 6 weeks in triplicate tanks (N = 3) in a recirculation aquaculture system. The 50% FM feed yielded significantly superior growth and growth efficiency in comparison with the 12% FM and 12% FM+ Soy PL feeds, but the 12% FM+ Marine PL feed yielded comparable results to 50% FM feed. A low‐water stress challenge induced elevated plasma glucose, cortisol and lactate levels in all treatments. However, a significant interaction (diet × stress) effect suggested a lesser cortisol response among fish fed the 12% FM+ Marine PL and 50% FM diets. These findings demonstrate that growth performance and, perhaps, resilience of cobia raised on reduced FM feeds may be improved by the addition of marine‐origin phospholipid to the diet.     

Efficacy of benzocaine as an anaesthetic for Crucian carp (Carassius carassius)

ObjectiveTo investigate the anaesthetic induction time and concentrations of stress markers in Crucian carp (Carassius carassius) subjected to different concentrations of benzocaine.Study designProspective experimental study.AnimalsThirty-six Crucian carp [body weight 368.3 ± 22.7 g and length 28.1 ± 1.9 cm (mean ± SD)].MethodsFish were divided into four groups, initially with nine fish per group. Each group was subjected to one of four final concentrations [0, 25, 50 and 100 parts per million (p.p.m.)] of benzocaine. The times to induction of sedation, to pre-anaesthesia and to anaesthesia were recorded according to the behavioural events observed after exposing the fish to benzocaine. At each stage, blood was collected from the caudal vein of three fish of the group, and these three fish were then euthanized. Plasma cortisol and glucose concentrations in the blood samples were measured as indices of stress response.ResultsInduction times for all stages of anaesthesia decreased significantly with increasing concentrations of benzocaine (1678 ± 103, 475 ± 73 and 251 ± 2 seconds for anaesthesia in 25, 50 and 100 p.p.m., respectively). Plasma cortisol and glucose concentrations were significantly lower in the anaesthetized groups than the control group (p < 0.05), and tended to decrease with an increasing dose of benzocaine. The cortisol concentrations (36.1 ± 5.8 ng dL^?1) at the anaesthetic stage for the 100 p.p.m. group were significantly decreased compared with the other groups (67.3 ± 14.9 ng dL^?1 in 25 p.p.m. and 47.6 ± 2.6 ng dL^?1 in 50 p.p.m.). Differences in glucose concentrations between benzocaine-treated groups were not significant.Conclusions and clinical relevanceIn this study, the fish group exposed to 100 p.p.m. benzocaine had a fast induction time for all monitored stages, low circulating cortisol and glucose concentrations and no immediate mortality.     

Three Myxosporeans Found in the Cranial and Branchial Tissues of Rainbow Trout in California

Abstract

Three myxosporeans were encountered in the cranial tissues of a California population of rainbow trout Oncorhynchus mykiss examined for the presence of Myxobolus cerebralis, the causative agent of whirling disease. Typical spores of M. cerebralis and a previously undescribed species of Myxobolus were found in the cranial tissues prepared by the pepsin HCl-trypsin digestion method. Henneguya zschokkei was also detected in digest preparations of cranial tissues, but was more numerous when branchial cartilage was included in the preparations. Microscopic examinations of tissues of individual rainbow trout showed occasional infections with both myxobolid species. Myxobolus cerebralis trophozoites and spores were found in the cranial and gill cartilage, and Myxobolus sp. was found in the brain and spinal cord. Henneguya zschokkei was also found within granulomas in the connective tissues below the gill arch. Both M. cerebralis and H. zschokkei were associated with a chronic inflammatory response in their respective tissues. In contrast, the Myxobolus sp. spores were found in pockets within the nervous tissues with no detectable host response. The spore measurements, calculated from fresh digests of infected tissues for the three myxosporeans (N = 20), for length × width × thickness in micrometers (SD) were 11.7 (0.6) without tails and 42.6 (5.2) with tails × 7.7 (0.8) × 7.0 (0.1) for H. zschokkei, 9.9 (0.4) × 8.4 (0.1) × 6.5 (0.3) for M. cerebralis, and 12.7 (0.7) × 10.5 (1.0) × 9.5 (0.8) for Myxobolus sp. Examined under scanning electron microscopy, the latter two species were morphologically similar although distinctive in size.     

Blood Parameters and Immune Status of Rainbow Trout with Proliferative Kidney Disease

Abstract

Blood parameters, disease resistance, and the immune response were sequentially evaluated in rainbow trout Oncorhynchus mykiss with proliferative kidney disease (PKD). The fish were maintained under laboratory conditions, and the study group went through a full cycle of the disease. Hematological and serological changes occurred primarily in those fish with severe kidney lesions. Fish infected with the parasite that causes PKD demonstrated a greater resistance to bacterial challenge, and their immune responses were heightened when compared with those of uninfected fish. These data suggest that PKD alone is not a predisposing factor for secondary infections if the fish does not incur severe renal lesions.     

Susceptibility of Selected Inland Salmonids to Experimentally Induced Infections with Myxobolus cerebralis,the Causative Agent of Whirling Disease

Abstract

Laboratory exposures to the infectious stages (triactinomyxons) of Myxobolus cerebralis demonstrated a range of susceptibility to whirling disease among four species of inland salmonids. Replicate groups of each species were exposed to two concentrations of triactinomyxons, a low dose (100–200 per fish) and a high dose (1,000–2,000 per fish). Exposed fish were evaluated for clinical signs, for severity of microscopic lesions at 35 d, 2 and 5 months, and for spore concentrations in the head cartilage at 5 months. A standard strain of rainbow trout Oncorhynchus mykiss matched for age served as a susceptible species control. Rainbow trout, westslope cutthroat trout O. clarki lewisi, Yellowstone cutthroat trout O. clarki bouvieri, and bull trout Salvelinus confluentus were susceptible to M. cerebralis infections. Clinical signs, including radical swimming (“whirling”) and black tails, were observed at 7 weeks postexposure among rainbow and cutthroat trout challenged at 3 weeks of age. Clinical signs were rare among bull trout exposed at an age of 4 weeks and absent among rainbow and cutthroat trout exposed at 3 months posthatch. Most rainbow, cutthroat, and bull trout were found to be infected when examined at 5 months postexposure. The most severe microscopic lesions among infected fish at 5 months postexposure were found among rainbow trout. Cutthroat trout had less severe lesions, bull trout had mild infections, and no evidence of infection was found among Arctic grayling Thymallus arcticus. Mean spore concentrations among infected fish correlated with the severity of microscopic lesion scores. Rainbow trout had mean concentrations of spores in head cartilage reaching 10⁶, whereas more resistant species such as bull trout had 10⁴ spores; no spores were found among Arctic grayling at 5 months postexposure.