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USGS1996

Control of external Aeromonas salmonicida: topical disinfection of salmonids with Chloramine-T

Brook trout Salvelinus fontinalis were treated with single 60-min static baths of 250 mg formalin/L, 3% NaCl, and 15 mg Chloramine-T/L to evaluate the efficacy of these compounds against external infections of Aeromonas salmonicida. Prevalence of A. salmonicida was significantly lower in brook trout treated with Chloramine-T than among those treated with formalin or salt. Further laboratory tests substantiated the therapeutic value of a single treatment of ChloramineT (15 mg/L) against A. salmonicida . In two experiments, viable counts of A. salmonicida in mucus did not vary among replicate groups of treated brook trout, but the counts for treated fish were significantly (P < 0.05) lower than those for untreated controls. In vitro tube dilution assays indicated that mean minimum inhibitory concentrations of Chloramine-T for 10 isolates of A. salmonicida were 9.0 mg/L for 1 h and 2.25 mg/L, for 24 h. In field trials at the White River National Fish Hatchery (Bethel, Vermont), the pathogen was detected principally as an external infection of juvenile Atlantic salmon Salmo solar maintained in two culture ponds. In one pond, the bacterium accounted for 100% of the total distribution of tnicroflora isolated from mucus. Seven days after treatment with Chloramine-T, A. sahnonicida accounted for 11% of the total bacterial counts identified from these fish. In the second pond, A. salmonicida composed 3% of the counts of bacteria isolated from the mucus of fish before treatment but was not isolated after treatment.

Journal of Aquatic Animal Health↗

USGS1997

Differences in detection of Aeromonas salmonicida in covertly infected salmonid fishes by the stress-inducible furunculosis test and culture-based assays

Accurate detection of Aeromonas salmonicida subsp. salmonicida (the cause of furunculosis disease) in covertly infected salmonids is difficult and is a cause of concern for those involved in fish health inspection and resource management programs. In this study, we examined populations of brook trout Salvelinus fontinalis , Atlantic salmon Salmo salar , and lake trout Salvelinus namaycush that previously sustained natural episodes of furunculosis. Consequently, the sampled fish were presumed to harbor latent infections. Mucus, gill, liver, kidney, heart, spleen, and intestine samples ( N = 100 fish per group sampled) were processed and examined by (1) direct dilution counts and (2) quadrant streaking after a 48‐h pre‐enrichment in trypticase soy broth (TSB). Another subsample of fish from each group was then subjected to stress‐inducible furunculosis tests. Stress tests detected A. salmonicida in three of four groups of fish that were examined whereas the pathogen was detected in only two of the groups analyzed with culture‐based assays. Although pre‐enrichment in TSB enhanced detection within internal sampling sites including the liver, heart, spleen, and kidney, enrichment did not enhance detection from mucus, gill, or intestinal samples.

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↗

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↗

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↗

USGS2000

Molecular epidemiology reveals emergence of a virulent infectious hematopoietic necrosis (IHN) virus strain in wild salmon and its transmission to hatchery fish

Infectious hematopoietic necrosis virus (IHNV) has been known to be a significant salmonid pathogen in the Pacific Northwest of North America for decades. The goal of this study was to characterize the IHNV genetic heterogeneity and viral traffic over time at a study site in the Deschutes River watershed in Oregon, with an emphasis on the epidemiology of IHNV types causing epidemics in wild kokanee Oncorhynchus nerka between 1991 and 1995. The study site included kokanee spawning grounds in the Metolius River and Lake Billy Chinook downstream, in which the IHNV epidemics occurred in 2- and 3-year-old kokanee, and the Round Butte Fish Hatchery at the outflow of the lake. Forty-two IHNV isolates collected from this area between 1975 and 1995 were characterized on a genetic basis by ribonuclease (RNase) protection fingerprint analyses of the virus nucleocapsid, glycoprotein, and nonvirion genes. Analysis of the 16 identified composite haplotypes suggested that both virus evolution and introduction of new IHNV strains contributed to the genetic diversity observed. The results indicated that the 1991–1995 epidemics in kokanee from Lake Billy Chinook were due to a newly introduced IHNV type that was first detected in spawning adult kokanee in 1988 and that this virus type was transmitted from the wild kokanee to hatchery fish downstream in 1991. Twelve IHNV haplotypes were found at Round Butte Fish Hatchery, indicating a series of virus displacement events during the 20-year period examined. This work shows that IHNV traffic can be much more complex than was previously recognized, and the results have implications for fisheries management at the hatchery and throughout the watershed.

Oregon↗

USGS2001

Epidemiology of viral hemorrhagic septicemia (VHS) among juvenile Pacific herring and Pacific sandlances in Puget Sound, Washington

Viral hemorrhagic septicemia (VHS) and the associated virus (VHSV) were identified in newly metamorphosed Pacific herring Clupea pallasi and Pacific sand lances Ammodytes hexapterus captured from Puget Sound, Washington, between 1995 and 1998. During that 4-year period, virus was detected in less than 1% of free-ranging, age-0 Pacific herring; however, when groups of these fish were confined in the laboratory, they experienced severe mortality, occasionally exceeding 50%, with the prevalence of VHSV reaching 100% by 14 d postcapture. At 7–21 d postcapture, VHSV titers peaked in excess of 108 plaque-forming units/g of tissue; by 30 d postcapture, however, the virus could no longer be isolated. Fish surviving beyond 30 d eliminated the virus from their tissues, but some remained lethargic and continued to show signs of hemorrhage around the mouth, skin, and fins until about 6 weeks postcapture. No cutaneous ulcers were observed during either the acute or the recovery phases of infection. Eighteen-month-old Pacific herring captured from the same area were also negative for VHSV but developed active infections after confinement for 7 d. Unlike younger fish, only 8.4% of these older fish died of VHS, and 7.7% of survivors were positive for VHSV at 7–10 d postcapture, which suggests that a higher proportion of the older fish had developed resistance to VHSV from prior exposure to it. Three months after fatalities ceased in the laboratory-held fish, the surviving fish were challenged with 5 3 103 plaque-forming units/mL of VHSV for 1 h. No mortality was observed during the next 30 d, and virus was recoverable at very low titers in fewer than 5% of the challenged fish, indicating the development of an active immunity to VHSV. Laboratory cohabitation of infected wild Pacific herring with laboratory-reared, specific-pathogen-free Pacific herring resulted in transmission of VHSV to the nonimmune fish, with the resulting course of disease resembling that seen in wild Pacific herring confined in the laboratory. The possible effects of VHS on stocks of Pacific herring are discussed.

Journal of Aquatic Animal Health↗

USGS2001

Reappraisal of the federal fish health recommendation for disinfecting eggs of Atlantic salmon iodophor

The U.S. Fish and Wildlife Service federal protocol for dual disinfection of fish eggs in 50 mg/L iodine solution for 30 min followed by a secondary disinfection in 100 mg/L iodine for 10 min was investigated during six spawning cycles of Atlantic salmon Salmo salar held at the Richard Cronin National Salmon Station (Sunderland, Massachusetts). This population of salmon had undergone an epizootic of furunculosis, and the surviving fish maintained a persistent infection of Aeromonas salmonicida throughout the course of study. Eggs from 20 individual paired matings of salmon were obtained annually during the first 2 weeks of November in each spawning cycle from 1995 through 2000 except for 1999, when fertilized eggs from 35 pairs of salmon were examined. Aeromonas salmonicida was isolated from 19 of the total 135 groups of fertilized eggs investigated during this study. In those cases, all isolations of the pathogen were made only in fertilized eggs that had not yet undergone disinfection in iodophor. In contrast to the results produced in the field, in vitro assays showed that A. salmonicida was not completely killed when initial concentrations of the bacterium ranged between 1.0 × 10 7 and 1.2 × 10 8 colony forming units (CFU)/mL. However, even when bacterial concentrations exceeded 1.0 × 10 7 CFU/mL, no A. salmonicida remained viable in eggs treated first with 50 mg/L iodine for 30 min and then with 100 mg/L iodine for 10 min, as prescribed in federal policy. Results of the current analysis also provided further evidence that A. salmonicida is not transmitted vertically through intra-ovum infection.

Massachusetts↗

USGS2002

Genetic characterization of infectious hematopoietic necrosis virus of coastal salmonid stocks in Washington State

Infectious hematopoietic necrosis virus (IHNV) is a pathogen that infects many Pacific salmonid stocks from the watersheds of North America. Previous studies have thoroughly characterized the genetic diversity of IHNV isolates from Alaska and the Hagerman Valley in Idaho. To enhance understanding of the evolution and viral transmission patterns of IHNV within the Pacific Northwest geographic range, we analyzed the G gene of IHNV isolates from the coastal watersheds of Washington State by ribonuclease protection assay (RPA) and nucleotide sequencing. The RPA analysis of 23 isolates indicated that the Skagit basin IHNV isolates were relatively homogeneous as a result of the dominance of one G gene haplotype (S). Sequence analysis of 303 bases in the middle of the G gene (midG region) of 61 isolates confirmed the high frequency of a Skagit River basin sequence and identified another sequence commonly found in isolates from the Lake Washington basin. Overall, both the RPA and sequence analysis showed that the Washington coastal IHNV isolates are genetically homogeneous and have little genetic diversity. This is similar to the genetic diversity pattern of IHNV from Alaska and contrasts sharply with the high genetic diversity demonstrated for IHNV isolates from fish farms along the Snake River in Idaho. The high degree of sequence and haplotype similarity between the Washington coastal IHNV isolates and those from Alaska and British Columbia suggests that they have a common viral ancestor. Phylogenetic analyses of the isolates we studied and those from different regions throughout the virus's geographic range confirms a conserved pattern of evolution of the virus in salmonid stocks north of the Columbia River, which forms Washington's southern border.

Washington↗

USGS2002

Incidence of Ichthyophonus hoferi in Puget Sound fishes and its increase with age of Pacific herring

A recent decrease in the mean age of adult Pacific herring Clupea pallasi in Puget Sound was associated with a high prevalence of Ichthyophonus hoferi , a protistan parasite that can be highly pathogenic to Pacific herring. In Puget Sound, high intensities of I. hoferi infection may be maintained in older cohorts of Pacific herring because the prevalence of I. hoferi increased with age from 12% among juveniles to 58% among the oldest, age-6 and older cohorts. Low intensities of I. hoferi infection in the region may be maintained in alternative fish hosts, such as surf smelt Hypomesus pretiosus , Puget Sound rockfish Sebastes emphaeus , Pacific tomcod Microgadus proximus , and speckled sanddab Cithanichthys stigmaeus .

Washington↗

USGS2002

Optimization of nested polymerase chain reaction assays for identification of Aeromonas salmonicida, Yersinia ruckeri and Flavobacterium psychrophilum

Nested polymerase chain reaction (PCR) assays were developed using first-round primers complementary to highly conserved regions within the bacterial 16S ribosomal RNA (rRNA) gene (universal eubacterial primers) and second-round primers specific for sequences within the 16S rRNA genes of Aeromonas salmonicida , Yersinia ruckeri , and Flavobacterium psychrophilum . Following optimization of the MgCl 2 concentration and primer annealing temperature, PCR employing the universal eubacterial primers was used to amplify a 1,500-base-pair (bp) product visible in agarose gels stained with ethidium bromide. The calculated detection limit of this single-round assay was less than 1.4 × 10 4 colony-forming units (CFU) per reaction for all bacterial species tested. Single-round PCR using primer sets specific for A. salmonicida , Y. ruckeri , and F. psychrophilum amplified bands of 271, 575, and 1,100 bp, respectively, with detection limits of less than 1.4 × 10 4 , 1.4 × 10 5 , and 1.4 × 10 5 CFU per reaction. Using the universal eubacterial primers in the first round and the species-specific primer sets in the second round of nested PCR assays improved the detection ability by approximately four orders of magnitude to fewer than 14 CFU per sample for each of the three bacterial species. Such nested assays could be adapted to a wide variety of bacterial fish pathogens for which 16S sequences are available.

Journal of Aquatic Animal Health↗

USGS2003

Efficacy of hydrogen peroxide in controlling mortality associated with saprolegniasis on walleye, white sucker, and paddlefish eggs

The efficacy of hydrogen peroxide in controlling saprolegniasis on eggs of walleye Stizostedion vitreum, white sucker Catostomus commersoni, and paddlefish Polyodon spathula was evaluated at four private, state, and federal production hatcheries participating in an Investigational New Animal Drug efficacy study (experiment 1; walleyes) and in a laboratory-based miniature egg jar incubation system (experiment 2; walleyes, white suckers, and paddlefish). Naturally occurring fungal infestations (saprolegniasis) were observed on eggs in both experiments. Confirmatory diagnosis of infested eggs from one hatchery in experiment 1 identified the pathogen as Saprolegnia parasitica. During experiment 1, eggs were treated daily for 15 min with either 0, 500, or 750 mg/L of hydrogen peroxide, and one trial compared a 500-mg/L hydrogen peroxide treatment with a formalin treatment at 1,667 mg/L. Saprolegniasis infestation was observed in control egg jars, whereas treatment with either formalin or hydrogen peroxide virtually eliminated the infestation. Hydrogen peroxide treatments of 500 mg/L either increased egg hatch or were as effective as physical removal of infested eggs in controlling mortality. Although treatment with formalin at 1,667 mg/L significantly increased the percent eye-up of walleye eggs compared with that of those treated with hydrogen peroxide at 500 mg/L, the difference was only 1.9-2.6%. In experiment 2, noneyed eggs were treated for 15 min every other day with 0, 283, 565, or 1,130 mg/L of hydrogen peroxide until the viable eggs hatched. Saprolegniasis infestation engulfed most control eggs, whereas infestation of treated eggs was either reduced or not visible. Hydrogen peroxide significantly increased egg hatch for all three species tested in experiment 2. Although hydrogen peroxide treatments as low as 283 mg/L significantly increased walleye and white sucker hatch, treatments between 500 and 1,000 mg/L are more likely to be effective in production egg incubation systems.

North American Journal of Aquaculture↗

USGS2003

Safety of oxytetracycline (Terramycin TM-100F) administered in feed to hybrid striped bass, walleyes, and yellow perch

Oxytetracycline (Terramycin TM-100F, a medicated premix containing oxytetracycline at 220 g/kg) is approved in the United States to control certain systemic bacterial diseases of salmon and catfish when fed at a rate of 55-82.5 mg per kilogram of bodyweight per day for 10 d. Although oxytetracycline may also control certain systemic bacterial infections in coolwater or scaled warmwater fish, no safety data for such species are available. Our objective was to determine the safety of oxytetracycline administered in feed at nominal doses of 0, 82.5, 248, or 413 mg??kg-1??d-1 to yellow perch Perca flavescens and hybrid striped bass (striped bass Morone saxatilis x white bass M. chrysops) for 10 d and to walleye Sander vitreus (formerly Stizostedion vitreum) for 20 d. Yellow perch and hybrid striped bass consumed 50% to 100% of the diet, whereas walleye feed consumption was occasionally less than 50% of the diet. Feed or fecal material was present in the gastrointestinal tract of all necropsied walleyes except for one control fish. The single growth effect was that hybrid striped bass offered a nominal dose of 413 mg??kg-1??d-1 were significantly smaller than untreated controls. Oxytetracycline-related histopathological findings were limited to walleyes and were of low severity. The histopathological findings included decreased hematopoietic-lymphopoietic (H&L) tissue in the anterior kidneys, diffuse hyperplasia of the gill filament epithelium, and a decreased prevalence of fish with eosinophilic droplets in their renal tubular epithelial cells. Although the incidence of decreased H&L tissue tended to increase in proportion to oxytetracycline dose, this finding was statistically significant only for fish that received a nominal dose of 413 mg??kg-1??d-1. Given the pathogenicity of the types of bacteria that are controlled by oxytetracycline treatment and the long history of its use in major aquaculture species, the relative risk of the minor oxytetracycline-related changes observed in this study may be outweighed by disease control benefits.

Journal of Aquatic Animal Health↗

USGS2007

Genetic diversity of infectious hematopoietic necrosis virus from Feather River and Lake Oroville, California, and virulence of selected isolates for Chinook salmon and rainbow trout

Infectious hematopoietic necrosis virus (IHNV) is a significant pathogen of young salmonid fishes worldwide but particularly within the historical range of the Pacific Northwest and California. In the Sacramento and San Joaquin River drainages of California, IHNV outbreaks in juvenile Chinook salmon Oncorhynchus tshawytscha have been observed regularly at large production hatcheries, including Coleman National Fish Hatchery (established in 1941) and Feather River State Fish Hatchery (FRH; established in 1967), since facility operations began. Recent severe epidemics at the FRH in 1998 and 2000-2002 prompted investigations into the characteristics and potential sources of virus at this facility. Both phylogenetic analyses of a variable portion of the glycoprotein gene and serologic comparisons based on neutralization with three polyclonal rabbit sera were used to characterize 82 IHNV isolates from the Feather River watershed between 1969 and 2004. All isolates examined were in the L genogroup and belonged to one of three serologic groups typical of IHNV from California. The IHNV isolates from the Feather River area demonstrated a maximum nucleotide sequence divergence of 4.0%, and new isolates appeared to emerge from previous isolates rather than by the introduction of more diverse subgroups from exogenous sources. The earliest isolates examined from the watershed formed the subgroup LI, which disappeared coincidently with a temporal shift to new genetic and serologic types of the larger subgroup LII. Experimental challenges demonstrated no significant differences in the virulence for juvenile Chinook salmon and rainbow trout O. mykiss from selected isolates representing the principal types of IHNV found historically and from recent epidemics at FRH. While most isolates were equally virulent for both host species, one isolate was found to be more virulent for Chinook salmon than for rainbow trout. ?? Copyright by the American Fisheries Society 2007.

Journal of Aquatic Animal Health↗

USGS2010

Susceptibility of three stocks of pacific herring to viral hemorrhagic septicemia

Laboratory challenges using specific-pathogen-free Pacific herring Clupea pallasii from three distinct populations indicated that stock origin had no effect on susceptibility to viral hemorrhagic septicemia (VHS). All of the populations were highly susceptible to the disease upon initial exposure, with significantly greater cumulative mortalities occurring in the exposed treatment groups (56.3-64.3%) than in the unexposed control groups (0.8-9.0%). Interstock differences in cumulative mortality were not significant. The virus loads in the tissues of fish experiencing mortality were 10-10,000 times higher during the acute phase of the epizootics (day 13 postexposure) than during the recovery phase (days 30-42). Survivors of the epizootics were refractory to subsequent VHS, with reexposure of VHS survivors resulting in significantly less cumulative mortality (1.2-4.0%) than among positive controls (38.1-64.4%); interstock differences in susceptibility did not occur after reexposure. These results indicate that data from experiments designed to understand the ecology of VHS virus in a given stock of Pacific herring are broadly applicable to stocks throughout the northeastern Pacific.

Journal of Aquatic Animal Health↗

USGS2006

Effects of live-well conditions on mortality and largemouth bass virus prevalence in largemouth bass caught during summer tournaments

We evaluated the effect of improved live-well conditions and the interaction of tournament stress and largemouth bass virus (LMBV) on tournament-associated mortality of largemouth bass Micropterus salmoides caught during 12 summer tournaments. Improvements in live-well conditions (reduction in water temperature by 2-5??C; addition of NaCl; continuous aeration) significantly reduced initial mortality of largemouth bass from 7% to 3% (F 1,11 = 10.29, P < 0.01). However, postrelease mortality of fish held for 5 d in net-pens or raceways was not reduced by the improved live-well conditions and averaged 76% for all tournament fish (F1,11 = 0.09, P = 0.77). The percentage of angler-caught fish infected with LMBV at the end of tournaments (14%) was significantly higher (P = 0.05) than the percentage infected in the general population (7%). The percentage of LMBV-infected fish increased during the post-tournament retention period to 64% for fish from live wells with improved conditions and 70% for fish from control live wells. Reference fish collected by electrofishing and held with tournament fish for 5 d also had high mortality (59%) and LMBV prevalence (47%), but these variables were significantly lower than those for tournament fish (mortality: F 2,30 = 3.63, P = 0.04; prevalence [Cochran-Mantel-Haenszel test]: P < 0.01). Many of the fish also had bacterial diseases during the post-tournament period, so the effect of LMBV on postrelease mortality could not be determined. However, the higher postrelease mortality of tournament and reference fish in our study relative to that observed in previous tournaments on lakes presumed free of LMBV suggests that this newly discovered pathogen influences measurement of post-tournament mortality. Increases in LMBV prevalence after typical fishing tournaments without prolonged post-tournament fish confinement will probably be lower than those we observed, but further research on the effects of LMBV on fish released from tournaments is warranted. ?? Copyright by the American Fisheries Society 2006.

North American Journal of Fisheries Management↗

USGS2008

Dispersal of Culex quinquefasciatus (Diptera: Culicidae) in a Hawaiian rain forest

Introduced mosquito-borne pathogens avian malaria (Plasmodium relictum Grassi and Feletti) and avian pox virus (Avipoxvirus) have been implicated in the past extinctions and declines of Hawaiian avifauna and remain significant obstacles to the recovery and restoration of endemic Hawaiian birds. Effective management of avian disease will require extensive mosquito control efforts that are guided by the local ecology of the vector Culex quinquefasciatus Say (Diptera: Culicidae). During October and November 1997 and September through November 1998 five mark-release-recapture experiments with laboratory-reared Cx. quinquefasciatus were conducted in a native rain forest on Hawaii Island. Of the overall 66,047 fluorescent dye-marked and released females, 1,192 (1.8%) were recaptured in 43-52 CO2-baited traps operated for 10-12-d trapping periods. Recaptured mosquitoes were trapped in all directions and at distances up to 3 km from the release site. The cumulative mean distance traveled (MDTs) over the trapping period ranged from a high of 1.89 km after 11 d (September 1998) to a low of 0.81 km after 11 d (November 1998). Released mosquitoes moved predominately in a downwind direction and they seemed to use forestry roads as dispersal corridors. Applying an estimated MDT of 1.6 km to a geographical information system-generated map of the Hakalau Forest National Wildlife Refuge clearly demonstrated that the effective refuge area could be reduced 60% by mosquitoes infiltrating into managed refuge lands. These findings should have significant implications for the design of future refuges and development of effective mosquito-borne avian disease control strategies.

Journal of Medical Entomology↗

USGS2014

Effect of temperature on feeding period of larval blacklegged ticks (Acari: Ixodidae) on eastern fence lizards

Ambient temperature can influence tick development time, and can potentially affect tick interactions with pathogens and with vertebrate hosts. We studied the effect of ambient temperature on duration of attachment of larval blacklegged ticks, Ixodes scapularis Say, to eastern fence lizards, Sceloporus undulatus (Bose & Daudin). Feeding periods of larvae that attached to lizards under preferred temperature conditions for the lizards (WARM treatment: temperatures averaged 36.6°C at the top of the cage and 25.8°C at the bottom, allowing behavioral thermoregulation) were shorter than for larvae on lizards held under cool conditions (COOL treatment temperatures averaged 28.4°C at top of cage and 24.9°C at the bottom). The lizards were infested with larvae four times at roughly monthly intervals. Larval numbers successfully engorging and dropping declined and feeding period was longer after the first infestation.

Journal of Medical Entomology↗