A practical guide to necropsy of the elasmobranch chondrocranium and causes of mortality in wild and aquarium-housed California elasmobranchs.

Elasmobranchs are common, iconic species in public aquaria; their wild counterparts are key members of marine ecosystems. Post-mortem examination is a critical tool for disease monitoring of wild elasmobranchs and for management of those under human care. Careful necropsy of the head, with a focus on clinically relevant anatomy, can ensure that proper samples are collected, increasing the chance of presumptive diagnoses prior to slower diagnostic workup. Immediate feedback from a thorough head necropsy allows for faster management decisions, often identifying pathogens, routes of pathogen entry, and pathogenesis, which are current shortcomings in published literature. This article proposes a protocol for necropsy of the elasmobranch chondrocranium, emphasizing unique anatomy and careful dissection, evaluation, and sampling of the endolymphatic pores and ducts, inner ears, brain, and olfactory system as part of a complete, whole-body necropsy. Extensive use of cytology and microbiology, along with thorough sample collection for histology and molecular biology, has proven effective in identifying a wide range of pathogens and assisting with characterization of pathogenesis. The cause of mortality is often identified from a head necropsy alone, but does not replace a thorough whole-body dissection. This protocol for necropsy and ancillary diagnostic sample collection and evaluation was developed and implemented in the necropsy of 189 wild and aquarium-housed elasmobranchs across 18 species over 13 years (2011-2023) in California. Using this chondrocranial approach, meningoencephalitis was determined to be the primary cause of mortality in 70% (118/168) of stranded wild and aquarium-housed elasmobranchs. Etiology was largely bacterial or protozoal. Carnobacterium maltaromaticum bacterial meningoencephalitis occurred in salmon sharks (Lamna ditropis), shortfin mako sharks (Isurus oxyrinchus), common thresher sharks (Alopias vulpinus), and one Pacific electric ray (Tetronarce californica). Miamiensis avidus was the most common cause of protozoal meningoencephalitis and found almost exclusively in leopard sharks (Triakis semifasciata) and bat rays (Myliobatis californica) that stranded in San Francisco Bay. Bacterial pathogens were found to use an endolymphatic route of entry, while protozoa entered via the nares and olfactory lamellae. Trauma was the second most common cause of mortality and responsible for 14% (24/168) of wild shark strandings and deaths of aquarium-housed animals.

spaB-positive Erysipelothrix rhusiopathiae, a novel teleost pathogen isolated from cultured barramundi.

Members of the genus Erysipelothrix are emergent pathogens of cultured eels, as well as several characid and cyprinid species. Since 2013, E. rhusiopathiae has been reported from diseased barramundi (Lates calcarifer) cultured in North America; we recovered 8 E. rhusiopathiae isolates from diseased fish during different outbreaks from the same farm. The E. rhusiopathiae isolates from barramundi were compared phenotypically and genetically to E. piscisicarius isolates characterized from ornamental fish and E. rhusiopathiae recovered from aquatic and terrestrial animals. All barramundi isolates were PCR-positive for the surface protective antigen type B (spaB) gene, and shared ≥ 99.7% sequence similarity among concatenated multilocus sequence analysis gene sequences, indicating a high degree of genetic homogeneity. These isolates were > 99% similar to other spaB-positive isolates from marine invertebrates and marine mammals, consistent with findings for other spa types. The spaA and spaB isolates shared < 98% similarity, as well as < 90% similarity with spaC-positive E. piscisicarius. Similar clonality among the spaB isolates was observed using repetitive element palindromic PCR. In experimental intracoelomic injection challenges conducted to fulfill Koch postulates, 67% of exposed tiger barbs (Puntigrus tetrazona) died within 14 d of challenge. Our study supports previous work citing the genetic variability of Erysipelothrix spp. spa types and the emergence of members of the genus Erysipelothrix as nascent fish pathogens.

DEXMEDETOMIDINE AND MIDAZOLAM INTRAMUSCULAR SEDATION IN BROWNBANDED BAMBOO SHARKS (CHILOSCYLLIUM PUNCTATUM).

Bamboo sharks are some of the most common elasmobranch species in zoos and aquaria and are frequently sedated for medical exams, treatments, and research. This study investigated the use of an IM sedation protocol of a single dose of dexmedetomidine (0.05 mg/kg) and midazolam (2.0 mg/kg) in brownbanded bamboo sharks (Chiloscyllium punctatum). Sharks were serially monitored every 5 min for heart rate, branchial beats, righting reflex, coelomic response, cloacal response, pelvic fin reflex, response to noxious stimulus, voluntary movement, and ability to swim. This sedation dose was effective at rapidly and significantly decreasing responses to tactile and noxious stimuli with minimal respiratory depression and was quickly reversible with atipamezole (0.5 mg/kg) and flumazenil (0.05 mg/kg). Sedated sharks developed a mild metabolic acidosis evidenced by a significant increase in lactic acid (mean < 0.37 mmol/L presedation, 4.2 mmol/L after reversal) and decrease in blood pH (mean 7.464 presedation, 7.277 after reversal); however, clinical intervention was not required. This protocol should be further investigated in different elasmobranch species but is promising for providing sedation for noninvasive procedures in brownbanded bamboo sharks.

Pathology, microbiology, and genetic diversity associated with Erysipelothrix rhusiopathiae and novel Erysipelothrix spp. infections in southern sea otters (Enhydra lutris nereis).

Erysipelothrix spp., including E. rhusiopathiae, are zoonotic bacterial pathogens that can cause morbidity and mortality in mammals, fish, reptiles, birds, and humans. The southern sea otter (SSO; Enhydra lutris nereis) is a federally-listed threatened species for which infectious disease is a major cause of mortality. We estimated the frequency of detection of these opportunistic pathogens in dead SSOs, described pathology associated with Erysipelothrix infections in SSOs, characterized the genetic diversity and antimicrobial susceptibility of SSO isolates, and evaluated the virulence of two novel Erysipelothrix isolates from SSOs using an in vivo fish model. From 1998 to 2021 Erysipelothrix spp. were isolated from six of >500 necropsied SSOs. Erysipelothrix spp. were isolated in pure culture from three cases, while the other three were mixed cultures. Bacterial septicemia was a primary or contributing cause of death in five of the six cases. Other pathology observed included suppurative lymphadenopathy, fibrinosuppurative arteritis with thrombosis and infarction, bilateral uveitis and endophthalmitis, hypopyon, petechia and ecchymoses, mucosal infarction, and suppurative meningoencephalitis and ventriculitis. Short to long slender Gram-positive or Gram-variable bacterial rods were identified within lesions, alone or with other opportunistic bacteria. All six SSO isolates had the spaA genotype-four isolates clustered with spaA E. rhusiopathiae strains from various terrestrial and marine animal hosts. Two isolates did not cluster with any known Erysipelothrix spp.; whole genome sequencing revealed a novel Erysipelothrix species and a novel E. rhusiopathiae subspecies. We propose the names Erysipelothrix enhydrae sp. nov. and Erysipelothrix rhusiopathiae ohloneorum ssp. nov. respectively. The type strains are E. enhydrae UCD-4322-04 and E. rhusiopathiae ohloneorum UCD-4724-06, respectively. Experimental injection of tiger barbs (Puntigrus tetrazona) resulted in infection and mortality from the two novel Erysipelothrix spp. Antimicrobial susceptibility testing of Erysipelothrix isolates from SSOs shows similar susceptibility profiles to isolates from other terrestrial and aquatic animals. This is the first description of the pathology, microbial characteristics, and genetic diversity of Erysipelothrix isolates recovered from diseased SSOs. Methods presented here can facilitate case recognition, aid characterization of Erysipelothrix isolates, and illustrate assessment of virulence using fish models.