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At least 109 records · Page 6Linked to original sources
USGS1998

Elicitation of macrophages from the peritoneal cavity of channel catfish

Four chemicals were evaluated for elicitation of macrophages in peritoneal cavities of 250–300‐g healthy channel catfish Ictalurus punctatus. Cellular exudates were collected at 3, 5, 7, 10, 14, and 20 d following intraperitoneal injections with squalene, Freund's incomplete adjuvant (FIA), goat serum, thioglycollate, or as a control, phosphate‐buffered saline. Injection with either squalene or FIA induced significantly greater ( P ⩽ 0.0001) macrophage recruitment than the other chemicals. The effectiveness of squalene and FIA was compared further by macrophage collection daily for 7 d. Squalene and FIA elicited similarly high macrophage responses ( P ⩽ 0.0450), the highest being 3.43 × 10 6 macrophages/mL (SE, 2.4 × 10 6 ) at 99% purity at day 2 and 2.1 × 10 6 macrophages/mL (SE, 0.7 × 10 6 ) at day 14 at 80% purity, respectively. In both experiments, the time after injection was not statistically significant, nor was there an interaction between time and chemicals. The occurrence of cells other than macrophages decreased with time to yield macrophage recoveries of 47–99% for squalene and 30–80% for FIA. Two subsets of macrophages were observed by means of flow cytometry. As demonstrated by chemiluminescence, the squalene‐elicited cells produced high‐energy oxygen compounds important to the phagocytic process.

Journal of Aquatic Animal Health↗
USGS1998

Biochemical and conjugation studies of romet-resistant strains of Aeromonas salmonicida from salmonid rearing facilities in the eastern United States

Strains of Aeromonas salmonicida ( n = 585) were collected from covertly infected and diseased salmonid hosts from 12 hatcheries in the eastern United States. Strains and sites were selected because of their potential for harboring antimicrobial resistance, in particular, to Romet™. Resistance to Romet was displayed by 315 strains (53.8%), which were isolated from all six host species sampled at 10 of 12 sites. Thirty of the resistant strains (9.5%) from five sites had no zone of inhibition, whereas the other strains had either confluent growth or resistant colonies within a zone of inhibition. Fifty-one resistant strains, representing each of the three resistance phenotypes, were selected for biochemical and antimicrobial comparisons with Romet-sensitive strains. All were confirmed to be A. salmonicida , and no characteristic biochemical phenotypes were found to be associated with resistance to Romet. Differential resistances between resistant and sensitive strains were detected to the antimicrobials oxytetracycline, tetracycline, sulfadiazine, sulfamethizole, trimethoprim, and SXT, a potentiated sulfonamide composed of trimethoprim and sulfamethoxazole. Plasmid DNA isolation and agarose gel electrophoresis were done for 25 Romet-resistant strains, and R-plasmids, not present in sensitive strains, were detected in 23 of these. Two different sizes of R-plasmids were detected, one about 55 kilobase pairs long and another about 50 kilobase pairs. Two strains isolated from New York brook trout Salvelinus fontinalis had reduced confluent growth within a zone of inhibition but contained no large plasmids. This may indicate chromosomally mediated resistance. Conjugational mating studies evaluated transfer of the R-plasmid DNA using eight Escherichia coli recipients. Successful R-plasmid transfer was accomplished with two donor strains (MI1 and MI2 from New Hampshire brook trout). Our results, in addition to those of other workers, illustrate the widespread resistance in A. salmonicida to approved antimicrobials and the capacity of this bacterium to become resistant in the fish culture environment.

Journal of Aquatic Animal Health↗
USGS1998

Isolation of Acholeplasma laidlawii from centrarchids in a Central Florida Lake

In 1991, the poor physical condition of largemouth bass Micropterus salmoides from Lake Harris, Florida, was associated with the decline of the lake's fishery. The swim bladders of emaciated bass had mild inflammation and ecchymotic hemorrhages. A mycoplasma-like organism isolated from swim bladders was initially believed to be the causative agent. The organism was later identified as Acholeplasma laidlawii by using a fluorescent antibody procedure and was demonstrated to be nonpathogenic. Parenteral injection of the organism into healthy largemouth bass fingerlings produced no signs of disease or difference in growth rate compared with control fish during a 16-month period. Field studies resulted in isolation of A. laidlawii from black crappies Pomoxis nigromaculatus , bluegills Lepomis macrochirus , and redear sunfish L. microlophus , but not from noncentrarchids in Lake Harris or from any fish species in a control fishery (Lake Holly, Florida). The absence of organisms in all emaciated bass, our inability to reproduce the disease, and isolation of the organism from seemingly healthy fish suggest this organism was not pathogenic.

Journal of Aquatic Animal Health↗
USGS1998

Infectious pancreatic necrosis virus: transmission from infectious to susceptible rainbow trout fry

Fry of rainbow trout Oncorhynchus mykiss were exposed to serotype VR-299 of infectious pancreatic necrosis virus (IPNV) by using a standardized immersion challenge. In concurrent experiments, fish were monitored for 11 d for excretion of IPNV or monitored for 9 d for excretion and transmission of IPNV to susceptible rainbow trout fry. Immersion-challenged fish began excreting virus within 2 d after challenge. The rate of IPNV excretion per fish increased steadily from about day 4 to day 8 and then decreased. Virus concentrations in tissues of immersion-challenged fish increased exponentially. Susceptible fish became infected with IPNV within 4 d after being introduced to immersion-challenged fish (e.g., 2 d after the challenged fish began excreting virus). By 9 d, 84% of the susceptible fish were infected with IPNV.

Journal of Aquatic Animal Health↗
USGS1998

Identification of Flavobacterinium and Flexibacterin species by species-specific polymerase chain reaction primers to the 16S ribosomal RNA gene

Species-specific polymerase chain reaction (PCR) primers have been developed for the identification of the causative agents of warmwater and marine finrot in fish: Flavobacterium columnare ( Flexibacter columnaris ) and Flexibacter maritimus. Differences in gene sequence in the bacterial small-subunit (16S) ribosomal RNA (rRNA) were used to design the species-specific PCR primers. The previously reported species-specific PCR primers Psy1 and Psy2 for the identification of Flavobacterium psychrophilum ( Flexibacter psychrophila ), the causative agent of coldwater finrot, were also used to develop a speciation scheme for all three bacterial finrots. These three primer sets were successful in discriminating among yellow-pigmented bacteria as well as in speciating the three major pathogenic flexibacteria to fish. The primer sets were designed to produce uniquely sized subproducts of 16S rRNA for each species: Flavobacterium psychrophilum (1,100 base pairs, bp), F. columnare (800 bp), and Flexibacter maritimus (400 bp). These primers were shown to correctly speciate field isolates in double-blind experiments ( P = 0.01).

Journal of Aquatic Animal Health↗
USGS1998

Determination of phylogenetic relationships of Flavobacterinium psychrophilum (Flexibacterin psychrophilus), Flavobacterinium columnare (Flexibacterin columnaris), and Flexibacterin maritimus by sequence analysis of 16S ribosomal RNA genes amplified by polymerase chain reaction

The nearly complete small subunit 16S ribosomal RNA (rRNA) gene sequence amplified by polymerase chain reaction was determined for Flavobacterium psychrophilum (formerly Flexibacter psychrophilus ) by using automated nucleotide sequencing. The sequence was found to be 1,465 base pairs (bp) in length, a size consistent with previously determined sequences for 14 other bacterial species from various taxa, including the yellow-pigmented bacteria. Sequence signatures confirmed that this organism was a member of the bacterial division Bacteroides–Flavobacterium. Parsimonious and additive phylogenetic trees were constructed with homology, and pairwise evolutionary distances were used to estimate phylogenetic relationships. Data show that F. psychrophilum, F. columnare , and Flexibacter maritimus are closely related, have a common descent, and represent a distinct group within the division Bacteroides–Flavobacterium. This group also included other organisms from the genera Flavobacterium and Cytophaga. Further, Flavobacterium aquatile , the type species for the genus Flavobacterium , was also determined to be a member of this “ Flavobacterium–Cytophaga–Flexibacter subcomplex.” This supports previous assertions that the type strain of Flavobacterium should be changed to a more representative species such as Flavobacterium breve .

Journal of Aquatic Animal Health↗
USGS1998

Vaccination of rainbow trout against infectious hematopoietic necrosis (IHN) by using attenuated mutants selected by neutralizing monoclonal antibodies

A neutralizing monoclonal antibody against infectious hematopoietic necrosis virus (IHNV) was used to select neutralization-resistant mutants from isolates of virus obtained from adult steelhead Oncorhynchus mykiss returning to the Round Butte Hatchery (RB mutants) on the Deschutes River in Oregon, USA, and from rainbow trout (nonanadromous O. mykiss) at a commercial hatchery in the Hagerman Valley of Idaho, USA (193-110 mutants). Two of the mutants, RB-1 and 193-110-4, were significantly (P < 0.001) attenuated compared with parental strains. Vaccination of rainbow trout by waterborne exposure to the mutants conferred solid protection against challenge with wild-type virus. In some trials, fish vaccinated with the RB-1 mutant at 50% tissue culture infectious doses (TCID50) of 1 X 104-1 x 105 TCID50/mL or with the 193-110-4 mutant at 1 x 102-1 x 103 TCID50/mL, held for 14 d, then challenged with the homologous wild-type strain at 1 x 105 TCID50/mL showed relative percent survival of 95-100% (P < 0.005). There was no significant difference (P > 0.05) in protection among fish exposed to the RB-1 vaccine strain at a dose of 1 x 105 TCID50/mL for periods of either 1, 12, or 24 h, held for 14 d, and then challenged with the wild-type RB isolate, although the 1-h exposure seemed to be somewhat less effective. Fish were vaccinated with the RB-1 strain at 1 x 103-1 x 105 TCID50/mL for 24 h then challenged after 1, 7, 14, or 21 d with the wild-type RB isolate. No significant (P > 0.1) protection was observed at 1 d postvaccination, but the relative percent survival increased progressively at each subsequent challenge period, becoming statistically significant by day 7 (P < 0.001) and beyond. These results suggested that resistance to challenge with wild-type virus resulted from development of IHNV-specific immunity and not from viral interference or interferon induction, and they reinforce the potential of an attenuated vaccine to control this important disease.

Journal of Aquatic Animal Health↗
USGS1998

Experimental infection of rainbow trout with Saprolegnia parasitica

A method was developed to experimentally induce saprolegniasis in rainbow trout Oncorhynchus mykiss. The development of a reliable method to produce infected fish is essential to efforts to determine the efficacy of various antifungal treatments. Three methods for inducing saprolegniasis were evaluated in waters containing known concentrations of Saprolegnia parasitica zoospores. These methods included application of the following stressors to fish: (1) abrasion and dewatering, (2) water temperature increase, and (3) a combination of abrasion, dewatering, and temperature increase. Neither physical abrasion nor temperature increase stress alone was effective for inducing saprolegniasis. Only 25.9% of fish stressed by abrasion and dewatering alone became infected. Application of both abrasion and temperature stress, however, induced saprolegniasis in 77.8% of fish tested. Most of these fish became infected after 5 d of stress treatments. No fish became infected or died in the positive control group (not stressed but exposed to S. parasitica zoospores) or the negative control group (not stressed or challenged). This method should enable researchers to induce saprolegniasis in rainbow trout to study its pathogenesis or to test the efficacy of antifungal treatments. In conducting efficacy studies, it is important that therapeutic treatments begin promptly after the first signs of saprolegniasis are observed because the disease can progress very quickly and often results in mortality.

Journal of Aquatic Animal Health↗
USGS1999

Characterization and inhibition of nitrite uptake in shortnose sturgeon fingerlings

Efforts are underway to culture the endangered shortnose sturgeon Acipenser brevirostrum for possible reintroduction. As part of a larger project to develop culture techniques for this species, the uptake of nitrite was evaluated in fingerlings (16.5 ± 4.85 g; mean ± SD). Plasma nitrite concentrations increased significantly with exposure time (0–5 d) and dose (0–4 mg nitrite-N/L). Shortnose sturgeon fingerlings were able to concentrate nitrite in their plasma to more than 63 times the environmental concentration. Chloride, as either sodium chloride or calcium chloride, partially inhibited nitrite uptake. However, calcium chloride was a better inhibitor. After previous exposure (2 d at 2.13 ± 0.080 mg nitrite-N/L) plasma nitrite-N decreased from 165.5 to 36.7 mg/L during a 3-d simultaneous exposure to 2.13 ± 0.080 mg nitrite-N/L and treatment with 40 mg chloride/L as calcium chloride. The addition of calcium chloride to the water appeared to be an effective means of preventing nitrite uptake and treating nitrite toxicity in hatchery-reared shortnose sturgeon fingerlings.

Journal of Aquatic Animal Health↗
USGS1999

A blood chemistry profile for lake trout

A blood chemistry profile for lake trout Salvelinus namaycush was developed by establishing baseline ranges for several clinical chemistry tests (glucose, total protein, amylase, alkaline phosphatase, alanine aminotransferase, aspartate aminotransferase, creatine kinase, calcium, and magnesium). Measurements were made accurately and rapidly with a Kodak Ektachem DT60 Analyzer and the Ektachem DTSC Module. Blood serum was collected from both laboratory-reared lake trout (1978 and 1986 year-classes) and feral spawning trout from Lake Michigan and then analyzed in the laboratory. No clinically significant differences were found between samples analyzed fresh and those frozen for 1 or 6 weeks. The ranges in chemistry variables for feral lake trout were generally wider than those for laboratory-reared lake trout, and significant differences existed between male and female feral lake trout for several tests. Blood chemistry profiles also varied seasonally on fish sampled repeatedly.

Journal of Aquatic Animal Health↗
USGS1999

Influence of infection with Renibacterium salmoninarum on susceptibility of juvenile spring chinook salmon to gas bubble trauma

During experiments in our laboratory to assess the progression and severity of gas bubble trauma (GBT) in juvenile spring chinook salmon Oncorhynchus tshawytscha , we had the opportunity to assess the influence of Renibacterium salmoninarum (Rs), the causative agent of bacterial kidney disease, on the susceptibility of salmon to GBT. We exposed fish with an established infection of Rs to 120% total dissolved gas (TDG) for 96 h and monitored severity of GBT signs in the fins and gills, Rs infection level in kidneys by using an enzyme-linked immunosorbent assay (ELISA), and mortality. Mortality occurred rapidly after exposure to 120% TDG, with a LT20 (time necessary to kill 20% of the population) of about 37 h, which is at a minimum about 16% earlier than other bioassays we have conducted using fish that had no apparent signs of disease. Fish that died early (from 31 to 36 h and from 49 to 52 h) had significantly higher infection levels (mean ?? SE ELISA absorbance = 1.532 ?? 0.108) than fish that survived for 96h (mean ?? SE ELISA absorbance = 0.828 ?? 0.137). Fish that died early also had a significantly greater number of gill filaments occluded with bubbles than those that survived 96 h. Conversely, fish that survived for 96 h had a significantly higher median fin severity ranking than those that died early. Our results indicate that fish with moderate to high levels of Rs infection are more vulnerable to the effects of dissolved gas supersaturation (DGS) and die sooner than fish with lower levels of Rs infection. However, there is a substantial amount of individual variation in susceptibility to the apparent cumulative effects of DGS and Rs infection. Collectively, our findings have important implications to programs designed to monitor the prevalence and severity of GBT in juvenile salmonids in areas like the Columbia River basin and perhaps elsewhere.

Journal of Aquatic Animal Health↗
USGS1999

Prevalence of Renibacterium salmoninarum in juvenile spring chinook salmon at Columbia and Snake river hatcheries, 1993-1996

We monitored the prevalence and severity of Renibacterium salmoninarum (RS) infections in juvenile hatchery spring chinook salmon Oncorhynchus tshawytscha at eight Columbia and Snake river hatcheries from 1993 through 1996. This study followed a prior study that monitored RS in the same hatcheries from 1988 through 1992. In the current study, we found that the prevalence of RS-positive fish declined at two hatcheries relative to the preceding 5 years. Prevalence dropped from near 90% in 1992 to below 50% at both sites by 1993 and was less than 20% at three locations in 1995. In contrast, prevalence increased at four of seven sites in 1993 and six of seven sites in 1994. This indicated that previously reported declines in RS prevalence at these locations might have been temporary. Our results showed that in 1993 the majority of fish at all monitored hatcheries had low RS-antigen levels and remained that way at most locations through 1996. These results suggest that certain hatchery practices may limit the severity of RS infections. Although elevations at two sites in 1994 and 1995 indicate reductions in RS were temporary in the short term, long-term monitoring will undoubtedly be required given the many factors that influence disease processes.

Journal of Aquatic Animal Health↗
USGS1999

Channel catfish response to ultraviolet-B radiation

Fingerling channel catfish Ictalurus punctatus exposed to simulated ultraviolet-B radiation at an average daily dose of 2.9 J/cm 2 were quite sensitive to the radiation. After a 24-h exposure, thinning of the most dorsal epidermis frequently was accompanied by edema. Compared with epidermis of unexposed fish, mucous cells in exposed fish were less superficial and club cells were less numerous both dorsally and high on the lateral surface of the body. Sunburn cells with pyknotic nuclei were evident in the epidermis of exposed fish. Among fish exposed for 48 h, focal necrosis and sloughing of the outer epidermal layer were widespread. A methanol-extractable skin substance that is associated with resistance to sunburn in other fish species was not detected in channel catfish.

Journal of Aquatic Animal Health↗
USGS1999

The potential role of natural tumor promoters in marine turtle fibropapillomatosis

Fibropapillomatosis (FP) in green turtles Chelonia mydas is a debilitating, neoplastic disease that has reached worldwide epizootic levels. The etiology of FP is unknown but has been linked to oncogenic viruses. Toxic benthic dinoflagellates (Prorocentrum spp.) are not typically considered tumorigenic agents, yet they have a worldwide distribution and produce a tumor promoter, okadaic acid (OA). Prorocentrum spp. are epiphytic on macroalgae and seagrasses that are normal components of green turtle diets. Here we show that green turtles in the Hawaiian Islands consume Prorocentrum and that high-risk FP areas are associated with areas where P. lima and P. concavum are both highly prevalent and abundant. The presence of presumptive OA in the tissues of Hawaiian green turtles further suggests exposure and a potential role for this tumor promoter in the etiology of FP.

Hawai'i↗
USGS1999

Aphanomyces as a cause of ulcerative skin lesions of menhaden from Chesapeake Bay Tributaries

During the summer and fall of 1997, an unusually high prevalence of skin lesions in fishes from Chesapeake Bay tributaries as well as two fish kills in the Pocomoke River stimulated significant public concern. Atlantic menhaden Brevoortia tyrannus were the most frequent target of the acute fish kills and displayed skin lesions that were attributed to the presence of the toxic dinoflagellate Pfiesteria piscicida. Hence, the penetrating skin ulcers so commonly found in this species are now widely viewed by the general public and some scientists as Pfiesteria -related and to be caused by exposure to Pfiesteria toxin. We examined, histologically, 121 menhaden with these ulcers collected from both Maryland and Virginia waters of the Chesapeake Bay in 1997 and 31 from the Pocomoke and Wicomico rivers in 1998. All of the deeply penetrating ulcers, as well as raised lesions (with or without eroded epithelium), were characterized by deeply penetrating fungal hyphae surrounded by chronic, granulomatous inflammation. These lesions had an appearance identical or similar to epizootic ulcerative syndrome (EUS), an ulcerative mycotic syndrome of fishes in other parts of the world caused by the fungal pathogen Aphanomyces invadans. They were also identical to ulcerative mycosis of menhaden previously reported along the Atlantic coast of the USA as associated with Aphanomyces spp. In 1998, using methods for isolation of A. invadans , we were able to culture from affected menhaden an Aphanomyces sp. that by preliminary tests is similar or identical to A. invadans. We believe these findings suggest that factors other than Pfiesteria toxin need to be considered as the cause or initiator of these lesions.

Journal of Aquatic Animal Health↗
USGS1999

Rate of disappearance of gas bubble trauma signs in juvenile salmonids

To assess the rate of disappearance of gas bubble trauma (GBT) signs in juvenile salmonids, we exposed spring chinook salmon Oncorhynchus tshawytscha and steelhead O. mykiss to water containing high levels of dissolved gas supersaturation (DGS) for a time period sufficient to induce signs of GBT, reduced the DGS to minimal levels, and then sampled fish through time to document changes in severity of GBT. Because of the tendency of GBT signs to dissipate at different rates, we conducted trials focusing on emboli (bubbles) in the gill filaments and lateral line and separate trials that focused on bubbles in the external surfaces (fins, eyes, and opercula). Bubbles in gill filaments dissipated almost completely within 2 h after transfer of fish to water of nearly normal DGS (104%), whereas bubbles in the lateral line dissipated to negligible levels within 5 h. Bubbles on external surfaces were more persistent through time than they were in gill filaments and the lateral line. Although typically dissipating to low levels within 48 h, external bubbles sometimes remained for 4 d. Assuming a direct relation exists between easily observable signs and direct mortality, our results suggest that fish can recover quickly from the potentially lethal effects of DGS once they move from water with high DGS to water of almost normal gas saturation. These results should be of fundamental importance to fishery managers interpreting the results of monitoring for the severity and prevalence of GBT in juvenile salmonids in the Columbia River system and perhaps elsewhere.

Journal of Aquatic Animal Health↗
USGS2000

Correlation of transforming growth factor-β messenger RNA (TGF-β mRNA) expression with cellular immunoassays in Triamcinolone-treated captive hybrid striped bass

Assessing fish immune status with molecular markers has been hampered by a lack of specific reagents. A quantitative polymerase chain reaction (PCR) method (reverse transcription quantitative–competitive PCR, RT-qcPCR) for measuring transforming growth factor-β (TGF-β) transcription from a broad range of teleost fish has recently been developed. The quantitative PCR now permits monitoring production of this important immunosuppressive cytokine in response to immunomodulating agents and conditions. We examined anterior kidney and spleen mononuclear cells from hybrid striped bass (female striped bass Morone saxatilis × male white bass M. chrysops ) for production of TGF-β messenger RNA (mRNA) in response to administration of the synthetic glucocorticoid triamcinolone. We also compared TGF-β transcription with anterior kidney macrophage bactericidal activity and splenic lymphocyte blastogenesis. Anterior kidney mononuclear cell TGF-β mRNA levels decreased, whereas bactericidal activity increased. Spleen TGF-β mRNA levels did not change significantly, and splenic lymphocyte pokeweed mitogen stimulation index increased in triamcinolone-treated fish. Since triamcinolone is used therapeutically as a suppressive immunomodulator, the enhanced immune functions indicated by the cellular immunoassays were unexpected; however, the inverse response of TGF-β production and macrophage bactericidal activity was consistent with the known relationship between TGF-β and macrophage activation in mammals. Induced immunomodulation in hybrid striped bass was detectable by both traditional cellular immunoassays and the new RT-qcPCR for TGF-β.

Journal of Aquatic Animal Health↗
USGS2000

Susceptibility of Arctic char to experimental challenge with Infectious Hematopoietic Necrosis Virus (IHNV) and Infectious Pancreatic Necrosis Virus (IPNV)

Arctic char Salvelinus alpinus were exposed to the fish pathogens infectious hematopoietic necrosis virus (IHNV) and infectious pancreatic necrosis virus (IPNV) to estimate susceptibility of the species to infection. Fish were immersion challenged at 46, 74, and 95 d posthatch for 5 h in viral concentration of 10 3 or 10 5 PFU(plaque-forming units)/mL and were monitored for 21 d postchallenge. Fish that died were assayed individually for virus-associated mortality, and survivors were assayed individually to estimate prevalence of virus carrier status. Arctic char succumbed to IHNV infection with population losses as high as 41%, and prevalence of IHNV carriers in surviving fish was 24% or less with virus titers in carrier fish ranging from 2.5 × 10 2 PFU/g to greater than 1.3 × 10 6 PFU/g. Infections with IPNV resulted in losses of 20% or less, and prevalence of IPNV carriers in surviving fish was as high as 82% with virus titers in carrier fish ranging from 2.5 × 10 2 PFU/g to greater than 5.0 × 10 6 PFU/g. Logistic regression models were developed for the mortality and infection data for each virus. For IHNV, the odds of dying or becoming infected were significantly greater for the fish from the 74-d age-group than for the fish from the 46-d or 95-d age-groups. Fish exposed to 10 5 PFU of IHNV/mL had significantly greater odds of dying or becoming infected than fish exposed to 10 3 PFU/mL. For IPNV, the odds of dying were significantly greater for the 74-d age-group compared with the other two age-groups. The 74-d fish were also significantly more likely to become infected than the 95-d-old fish. Fish exposed to 10 5 PFU of IPNV/mL had significantly greater odds of dying or becoming infected than fish exposed to 10 3 PFU of IPNV /mL.

Journal of Aquatic Animal Health↗