Heart inflammation and piscine orthoreovirus genotype-1 in Pacific Canada Atlantic salmon net-pen farms: 2016-2019.

Piscine orthoreovirus genotype-1 (PRV-1) is a virus commonly associated with Atlantic salmon aquaculture with global variability in prevalence and association with disease. From August 2016 to November 2019, 2,070 fish sampled at 64 Atlantic salmon net-pen farm sites during 302 sampling events from British Columbia, Canada, were screened for PRV-1 using real-time qPCR. Nearly all populations became PRV-1 positive within one year of seawater entry irrespective of location, time of stocking, or producer.

Innate antiviral defense demonstrates high energetic efficiency in a bony fish.

Background: Viruses can impose energetic demands on organisms they infect, in part by hosts mounting resistance. Recognizing that oxygen uptake reliably indicates steady-state energy consumption in all vertebrates, we comprehensively evaluated oxygen uptake and select transcriptomic messaging in sockeye salmon challenged with either a virulent rhabdovirus (IHNV) or a low-virulent reovirus (PRV). We tested three hypotheses relating to the energetic costs of viral resistance and tolerance in this vertebrate system: (1) mounting resistance incurs a metabolic cost or limitation, (2) induction of the innate antiviral interferon system compromises homeostasis, and (3) antiviral defenses are weakened by acute stress.

Cross-sectional study of histopathology and piscine orthoreovirus during a marine production cycle of farmed Atlantic salmon (Salmo salar L.) in British Columbia, Canada.

Two cohorts of farmed Atlantic salmon, Salmo salar L., in British Columbia, Canada, were sampled for histopathology (nine organs) and piscine orthoreovirus (PRV-1) PCR after seawater entry at 2, 4, 6, 8, 10, 13, 16 and 19 months (20 fish per cohort per date). One cohort-from a PRV+ hatchery-remained PRV+ throughout the study (sample prevalence 80%-100%).

Author Correction: Piscine orthoreovirus demonstrates high infectivity but low virulence in Atlantic salmon of Pacific Canada.

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

Piscine orthoreovirus demonstrates high infectivity but low virulence in Atlantic salmon of Pacific Canada.

Piscine orthoreovirus (PRV) is ubiquitous in farmed Atlantic salmon and sometimes associated with disease - most notably, Heart and Skeletal Muscle Inflammation (HSMI). However, PRV is also widespread in non-diseased fish, particularly in Pacific Canada, where few cases of severe heart inflammation have been documented. To better understand the mechanisms behind PRV-associated disease, this study investigated the infection dynamics of PRV from Pacific Canada and the potential for experimental passage of putatively associated heart inflammation in Pacific-adapted Mowi-McConnell Atlantic salmon.

Development of a PCR assay to detect cyprinid herpesvirus 1 in koi and common carp.

Cyprinid herpesvirus 1 (CyHV1) infects all scaled and color varieties of common carp Cyprinus carpio, including koi. While it is most often associated with unsightly growths known as 'carp pox,' the underlying lesion (epidermal hyperplasia) can arise from a variety of disease processes. CyHV1-induced epidermal hyperplasia may occur transiently in response to water temperature, and thus histopathology cannot be used in isolation to assess CyHV1 infection status.

Piscine Orthoreovirus from Western North America Is Transmissible to Atlantic Salmon and Sockeye Salmon but Fails to Cause Heart and Skeletal Muscle Inflammation.

Heart and skeletal muscle inflammation (HSMI) is a significant and often fatal disease of cultured Atlantic salmon in Norway. The consistent presence of Piscine orthoreovirus (PRV) in HSMI diseased fish along with the correlation of viral load and antigen with development of lesions has supported the supposition that PRV is the etiologic agent of this condition; yet the absence of an in vitro culture system to demonstrate disease causation and the widespread prevalence of this virus in the absence of disease continues to obfuscate the etiological role of PRV with regard to HSMI. In this study, we explore the infectivity and disease causing potential of PRV from western North America-a region now considered endemic for PRV but without manifestation of HSMI-in challenge experiments modeled upon previous reports associating PRV with HSMI.

Protective immunity of a modified-live cyprinid herpesvirus 3 vaccine in koi (Cyprinus carpio koi) 13 months after vaccination.

Objective: To evaluate the long-term protective immunity of a cyprinid herpesvirus 3 (CyHV3) vaccine in naïve koi (Cyprinus carpio koi).

Animals: 72 koi. Procedures-Vaccinated koi (n = 36) and unvaccinated control koi (36) were challenge exposed to a wild-type CyHV3 strain (KHVp8 F98-50) 13 months after vaccination.

Efficacy and safety of a modified-live cyprinid herpesvirus 3 vaccine in koi (Cyprinus carpio koi) for prevention of koi herpesvirus disease.

Objective: To investigate safety and efficacy of a cyprinid herpesvirus type 3 (CyHV3) modified-live virus vaccine for the prevention of koi herpesvirus disease (KHVd).

Animals: 420 healthy koi (Cyprinus carpio koi).

Procedures: Fish were vaccinated with a 1× dose or 10× overdose of CyHV3 modified-live virus vaccine or a placebo through bath exposure in tanks at 22°C.

Systemic iridovirus from threespine stickleback Gasterosteus aculeatus represents a new megalocytivirus species (family Iridoviridae).

Megalocytiviruses have been associated with epizootics resulting in significant economic losses in public aquaria and food-fish and ornamental fish industries, as well as threatening wild fish stocks. The present report describes characteristics of the first megalocytivirus from a wild temperate North American fish, the threespine stickleback Gasterosteus aculeatus. Moribund and dead fish sampled after transfer to quarantine for an aquarium exhibit had amphophilic to basophilic intracytoplasmic inclusions (histopathology) and icosahedral virions (transmission electron microscopy) consistent with an iridovirus infection.

Relationship of farm salmon, sea lice, and wild salmon populations.

Increased farm salmon production has heightened concerns about the association between disease on farm and wild fish. The controversy is particularly evident in the Broughton Archipelago of Western Canada, where a high prevalence of sea lice (ectoparasitic copepods) was first reported on juvenile wild pink salmon (Oncorhynchus gorbuscha) in 2001. Exposure to sea lice from farmed Atlantic salmon (Salmo salar) was thought to be the cause of the 97% population decline before these fish returned to spawn in 2002, although no diagnostic investigation was done to rule out other causes of mortality.

Failure of population recovery in relation to disease in Pacific herring.

Following an estimated 60% decline in population abundance in early 1993, recovery of the Pacific herring Clupea pallasii population of Prince William Sound, Alaska, USA, has been impaired by disease. Comprehensive epidemiological study from 1994 through 2002 validated an age-structured assessment (ASA) model of disease and population abundance; from 2003 to 2006, the impact of disease was modeled by analyzing only 2 lesions: ulcers and white foci in the heart. The ASA model identified increased natural mortality since 1993 that can be explained by (1) epidemics associated with ulcers (prevalence about 3%) and the North American strain of viral hemorrhagic septicemia virus (VHSV Type IVa; prevalence up to 14%) in 1994 and 1998 and (2) relatively high prevalence of the mesomycetozoean Ichthyophonus hoferi from 1994 through 2006, including epidemics with the greatest sample prevalence in 2001 (38%, by histopathology) and 2005 (51%, estimated histopathology prevalence).

Ruptured yolk sacs and visceral fungi in emergent pink salmon alevins: histopathology and relation to marine survival.

Marine survival of anadromous salmon species is highly variable, and causes of this variability are often unknown. In the 1990s, cultured pink salmon Oncorhynchus gorbuscha alevins from 2 different regions in Alaska, USA, had years with increased postemergent mortality that could not be attributed to viruses, bacteria, or parasites. In both regions, lifetime marine survival of the most severely affected fish groups was as low as 1.

Fish cardiovascular physiology and disease.

Fish patients with cardiovascular disorders present a challenge in terms of diagnostic evaluation and therapeutic options. Veterinarians can approach these cases in fish using methods similar to those employed for other companion animals. Clinicians who evaluate and treat fish in private, aquarium, zoologic, or aquaculture settings need to rely on sound clinical judgment after thorough historical and physical evaluation.

Finfish and aquatic invertebrate pathology resources for now and the future.

Utilization of finfish and aquatic invertebrates in biomedical research and as environmental sentinels has grown dramatically in recent decades. Likewise the aquaculture of finfish and invertebrates has expanded rapidly worldwide as populations of some aquatic food species and threatened or endangered aquatic species have plummeted due to overharvesting or habitat degradation. This increasing intensive culture and use of aquatic species has heightened the importance of maintaining a sophisticated understanding of pathology of various organ systems of these diverse species.

The effect of chronic chromium exposure on the health of Chinook salmon (Oncorhynchus tshawytscha).

This study was designed to determine fish health impairment of Chinook salmon (Oncorhynchus tshawytscha) exposed to chromium. Juvenile Chinook salmon were exposed to aqueous chromium concentrations (0-266 microgl(-1)) that have been documented in porewater from bottom sediments and in well waters near salmon spawning areas in the Columbia River in the northwestern United States. After Chinook salmon parr were exposed to 24 and 54 microg Crl(-1) for 105 days, neither growth nor survival of parr was affected.

Evaluation of five diagnostic methods for the detection and quantification of Myxobolus cerebralis.

Diagnostic methods were used to identify and quantify Myxobolus cerebralis, a myxozoan parasite of salmonid fish. In this study, 7-week-old, pathogen-free rainbow trout (Oncorhynchus mykiss) were experimentally infected with M. cerebralis and at 7 months postinfection were evaluated with 5 diagnostic assays: 1) pepsin-trypsin digest (PTD) to detect and enumerate spores found in cranial cartilage, 2) 2 different histopathology grading scales that provide a numerical score for severity of microscopic lesions in the head, 3) a conventional single-round polymerase chain reaction (PCR), 4) a nested PCR assay, and 5) a newly developed quantitative real-time TaqMan PCR.

Retrospective analysis: bile hydrocarbons and histopathology of demersal rockfish in Prince William Sound, Alaska, after the Exxon Valdez oil spill.

Demersal rockfish are the only fish species that have been found dead in significant numbers after major oil spills, but the link between oil exposure and effect has not been well established. After the 1989 Exxon Valdez oil spill in Prince William Sound, Alaska, several species of rockfish (Sebastes spp.) from oiled and reference sites were analyzed for hydrocarbon metabolites in bile (1989-1991) and for microscopic lesions (1990 and 1991).

Susceptibility of two strains of rainbow trout (one with suspected resistance to whirling disease) to Myxobolus cerebralis infection.

The susceptibility of 2 strains of rainbow trout Oncorhynchus mykiss, 1 from North America (TL) and 1 from Germany (GR), to Myxobolus cerebralis (the cause of salmonid whirling disease) was assessed following exposure to the infectious stages (triactinomyxons). Two laboratory experiments were conducted with age-matched rainbow trout of each strain. At the beginning of the study, the 2 trout strains were aged ca.