Pathology of Tumors in Fish Associated With Retroviruses

Cytology of a seminoma in a koi (Cyprinus carpio): a rapid diagnostic tool

Koi(Cyprinus carpio) is an ornamental variety of common carp frequently kept as pets. Given their long lifespan, neoplasia, albeit uncommon, may occur in these animals, and only a few studies have faced their cytological diagnosis. In the present case, a koi carp was referred to the clinicians due to coelomic swelling. The carp underwent surgery, which revealed an enlargement of both testes. Testicular samples were cytologically and histologically examined. The lesion was diagnosed as a seminoma since it was composed of round, large, atypical, and often multinucleated cells with round central nuclei and moderate cytoplasm. These tumors had the same appearance as seminomas in mammals and should be considered among differential diagnoses when coelomic swelling occurs in koi carp. Seminomas in koi carp are diagnosed histologically, but cytology, a rapid and cheap exam executable in all veterinary clinical facilities, could be a relevant preliminary diagnostic tool that may influence the entire diagnostic process.

Retrospective Study of the Prevalence, Histopathology, Therapy, and Survival Time of Neoplastic Disease in Fish

This study evaluated neoplasia in fish using medical records from zoos, aquariums, and exotic animal veterinarians. The parameters evaluated included geographic location, habitat type, signalment, anatomic location of neoplasia, type of neoplasia as confirmed with histologic examination, survival time, and treatments provided for each patient. These data were entered into the Exotic Species Cancer Research Alliance (ESCRA) database. Out of 455 cases from across the United States and England, most animals submitted were from zoologic parks or aquariums (62.9%), followed by private ownership (1.5%). The percent of female (19.3%) and male (17.8%) patients were similar, and the mean age at the time of diagnosis was 99.45 months, with a range of 12 to 300 months. The species with the highest neoplasia prevalence was koi (18.5%), followed by goldfish (10.8%). The eye was the most commonly reported site for a primary neoplasm (8.4%), and the most prevalent diagnosis across all organ systems was soft tissue sarcoma (26.2%). Only 13 patients in this study (2.9%) received any form of treatment, with a mean survival time of 8.85 months post-treatment. These data demonstrate that while information related to clinical therapy of cancer in fish species is lacking, surgical excision of tumors in fish, when feasible for the patient and client, may improve patient outcomes.

PRIMARY HEPATIC NEOPLASIA IN THREE ADULT BAMBOO SHARKS (CHILOSCYLLIUM PLAGIOSUM AND CHILOSCYLLIUM PUNCTATUM) IN AN AQUARIUM POPULATION

Neoplasia in elasmobranchs is uncommonly documented. This report describes primary hepatic neoplasia in three adult female bamboo sharks under managed care: biliary adenocarcinoma in a whitespotted bamboo shark (Case 1; Chiloscyllium plagiosum), biliary adenocarcinoma in a brownbanded bamboo shark (Case 2; Chiloscyllium punctatum), and hepatocellular carcinoma in a whitespotted bamboo shark (Case 3). Case 1 presented with extensive cutaneous papillomas and was electively euthanized. At necropsy, a 4-cm-diameter, pale-tan, firm hepatic mass was identified and diagnosed histologically as a biliary adenocarcinoma. Case 2 presented with decreasing body condition despite normal food intake. Coelomic ultrasound and exploratory surgery revealed several large masses in both hepatic lobes, and the patient was euthanized. At necropsy, nine, 1-6-cm-diameter, black to tan, firm hepatic masses were identified and diagnosed histologically as biliary adenocarcinoma with branchial intravascular neoplastic emboli. Case 3 presented for routine health examination and was euthanized for diagnostic purposes after coelomic ultrasound revealed multiple hepatic masses. At necropsy, two 1-3-cm-diameter, brown- and-black mottled, firm hepatic masses were identified and diagnosed histologically as hepatocellular carcinoma. Immunohistochemistry was performed in two of these cases and was noncontributory, likely because of a lack of cross reactivity between antibodies (antipancytokeratin) and elasmobranch tissues.

Cutaneous epitheliotropic lymphosarcoma in a captive white catfish (Ameiurus catus Linnaeus)

A wild caught white catfish (Ameiurus catus Linnaeus) developed multiple cutaneous masses. Cytology revealed neoplastic lymphocytes and microscopy confirmed dermal infiltration with epitheliotropism in the epidermis, oral mucosa, and cornea, without internal organ involvement. Transmission electron microscopy did not identify viral particles. Histopathology supported cutaneous epitheliotropic lymphosarcoma, a condition most commonly reported in mammals. This is the first reported case of cutaneous epitheliotropic lymphosarcoma in an ictalurid and one of the few published cases of this condition in any fish species.

Gular Cutaneous Fibrosarcoma and Anatomophysiological Considerations for Anaesthesia in a Saddled Bichir, Polypterus endlicheri endlicheri

Bichirs (Polypterus spp.) have frequently been studied with regard to comparative and developmental anatomy; however, very little information has been published regarding diseases, aging changes, and medical and surgical management in these species. Neoplasia represents one such example of conditions for which a dearth of information in these species exists. There has been increasing recognition of various types of neoplasms, including cutaneous tumors, particularly in ornamental fish; some of which may be related to environmental or to infectious causes. When excision of such tumors is indicated, surgical anaesthesia is required. However, special considerations may be warranted when employing immersion anaesthesia protocols in facultative air-breathing fish that can utilise the lungs for respiration. This anatomophysiological feature of Polypterus spp. may not only influence induction and maintenance of surgical anaesthesia but may theoretically have implications for drowning. Herein, we describe the management of a case of a rapidly growing gular neoplasm in a juvenile saddled bichir and considerations for surgical anaesthesia in this “lunged” species. Induction and maintenance of surgical anaesthesia using tricaine methanesulfonate (MS-222) in this species were found to be effective at significantly lower concentrations than standard recommended doses. Histopathological analysis identified the mass as a fibrosarcoma. To the best of our knowledge, this is the first report of a cutaneous fibrosarcoma in a bichir, representing the first report of neoplasia in Polypterus spp. and the first description of surgical anaesthesia in this amphibious fish.

The evolution and ecology of benign tumors

Tumors are usually classified into two main categories - benign or malignant, with much more attention being devoted to the second category given that they are usually associated with more severe health issues (i.e., metastatic cancers). Here, we argue that the mechanistic distinction between benign and malignant tumors has narrowed our understanding of neoplastic processes. This review provides the first comprehensive discussion of benign tumors in the context of their evolution and ecology as well as interactions with their hosts. We compare the genetic and epigenetic profiles, cellular activities, and the involvement of viruses in benign and malignant tumors. We also address the impact of intra-tumoral cell composition and its relationship with the tumoral microenvironment. Lastly, we explore the differences in the distribution of benign and malignant neoplasia across the tree of life and provide examples on how benign tumors can also affect individual fitness and consequently the evolutionary trajectories of populations and species. Overall, our goal is to bring attention to the non-cancerous manifestations of tumors, at different scales, and to stimulate research on the evolutionary ecology of host-tumor interactions on a broader scale. Ultimately, we suggest that a better appreciation of the differences and similarities between benign and malignant tumors is fundamental to our understanding of malignancy both at mechanistic and evolutionary levels.

Peripheral Nerve Sheath Tumors Resembling Human Atypical Neurofibroma in Goldfish (Carassius auratus, Linnaeus, 1758)

Simple Summary

In animals, especially in fish, dermal neoplasms are a common finding. A distinction between peripheral nerve sheath tumors (PNSTs) and other spindle cell tumors (SCTs) is not always possible when relying exclusively on routine cytological and histopathological findings. The current study aims to determine a minimal subset of stains required to correctly identify PNSTs in goldfish and describes, in detail, six dermal nodules that resemble atypical neurofibroma in humans. Interestingly, muscular and fibroblastic tumors were excluded using Azan trichrome staining, while Alcian blue and Gomori’s reticulin stains revealed the presence of intratumoral areas of mucins and basement membrane fragments, respectively. In addition, PAS and PAS with diastase pretreatment confirmed the latter finding and revealed intra- and extracellular glycogen granules. Immunohistochemistry displayed reactivity for S100 protein, CNPase, and phosphorylated and non-phosphorylated neurofilament-positive axons. Altogether, these findings suggested that Azan trichrome staining, Gomori’s reticulin staining, and immunohistochemistry for S100 protein and CNPase represent a useful set of stains to identify and characterize PNSTs in goldfish.

Abstract

Skin spindle cell tumors (SSTs) frequently occur in fishes, with peripheral nerve sheath tumors (PNSTs) being the most commonly reported neoplasms in goldfish. However, distinguishing PNSTs from other SCTs is not always possible when relying exclusively on routine cytological and histopathological findings. Therefore, the aim of this study is to characterize six skin nodules, resembling atypical neurofibromas in humans, found in six cohabiting goldfish (Carassius auratus), and to determine a minimal subset of special stains required to correctly identify PNSTs in this species. Routine cytology and histopathology were indicative of an SCT with nuclear atypia in all cases, with randomly distributed areas of hypercellularity and loss of neurofibroma architecture. Muscular and fibroblastic tumors were excluded using Azan trichrome staining. Alcian blue and Gomori’s reticulin stains revealed the presence of intratumoral areas of glycosaminoglycans or mucins and basement membrane fragments, respectively. PAS and PAS–diastase stains confirmed the latter finding and revealed intra- and extracellular glycogen granules. Immunohistochemistry displayed multifocal, randomly distributed aggregates of neoplastic cells positive for S100 protein and CNPase, intermingled with phosphorylated and non-phosphorylated neurofilament-positive axons. Collectively, these findings are consistent with a PNST resembling atypical neurofibroma in humans, an entity not previously reported in goldfish, and suggest that Azan trichrome staining, reticulin staining, and immunohistochemistry for S100 protein and CNPase represent a useful set of special stains to identify and characterize PNSTs in this species.

Sudden outbreak of metastatic intestinal adenocarcinoma in rainbow trout Oncorhynchus mykiss

Intestinal adenocarcinomas are uncommon in fishes. To date, they have been reported in zebrafish Danio rerio, blue gularis Fundulopanchax sjostedti, koi carp Cyprinus carpio koi, Atlantic salmon Salmo salar and rainbow trout Oncorhynchus mykiss. Metastases are even rarer and have been observed so far at very low prevalence, only in feed-induced adenocarcinoma in Atlantic salmon and rainbow trout. Intestinal adenocarcinoma with liver and heart metastases and mesenteric invasion was found in approximately 33% of 4 yr old rainbow trout from a Slovene hatchery with 2000 breeding trout. During stripping, lumps in the abdominal cavity were palpated in one-third of the breeding fish; some of the fish were anorectic and lethargic, and mortality was slightly increased. Affected trout were euthanized and 4 were submitted for necropsy and histopathology. Necropsy revealed firm, whitish, irregularly lobular masses originating from the intestine. Histologically, the intestinal masses showed a prominent proliferation of tall columnar neoplastic epithelial cells arranged in dense irregular islands or solid areas and papillotubular protuberances. Solid areas of neoplastic cells were also observed in the mesentery of all trout and in the liver of one trout, whereas minute groups of neoplastic cells were seen in the vessels of the intestinal mucosa in all trout and in the myocardium and the liver of one trout. Epithelial origin of neoplastic cells was confirmed by expression of the cytokeratin marker AE1/AE3. The intestinal masses were diagnosed as intestinal adenocarcinoma with mesenteric invasion and metastases to the liver and heart. The cause of intestinal adenocarcinoma was not determined.

Epizootic neoplasia in a managed population of Atlantic bumper fish, Chloroscombrus chrysurus (Osteichthyes: Carangidae), at a public aquarium

Advances in fish medicine and husbandry have increased the average lifespans of specimens in managed aquarium populations. As a result, an increased incidence and variety of neoplasia is expected. This work characterizes diverse neoplasms arising within a managed population of Atlantic bumper fish acquired via repeated collections from the Charleston Harbor region. A total of 76 neoplasms were evaluated histologically from 41 of 45 fish that died or were killed over a 46-month period, including cutaneous hemangiomas and hemangiosarcomas, lepidocytomas and lepidosarcomas, fibromas, vertebral body or cutaneous osteomas, disseminated lymphomas, testicular leiomyomas, cutaneous or branchial fibrosarcomas, myxomas, fibroblastic lepidosarcoma, teratoid medulloepithelioma, ganglioglioma, malignant nerve sheath tumour, cardiac rhabdomyoma, cutaneous rhabdomyosarcoma, soft tissue sarcoma and renal adenoma. Perioral and cutaneous lesions of vascular and scale origin were observed most frequently. Other, often malignant, neoplasms arose within these benign lesions, resulting in extensive local tissue invasion. However, excluding disseminated lymphomas, metastasis was only detected in one case of hemangiosarcoma. These findings suggest early surgical intervention may limit tissue destruction and loss of display quality. This report details a variety of common and rare neoplasms in fish, as well as the first characterizations of neoplasia in Atlantic bumper and ganglioglioma in fish.

Research-Relevant Background Lesions and Conditions in Common Avian and Aquatic Species

Non-mammalian vertebrates including birds, fish, and amphibians have a long history of contributing to ground-breaking scientific discoveries. Because these species offer several experimental advantages over higher vertebrates and share extensive anatomic and genetic homology with their mammalian counterparts, they remain popular animal models in a variety of fields such as developmental biology, physiology, toxicology, drug discovery, immunology, toxicology, and infectious disease. As with all animal models, familiarity with the anatomy, physiology, and spontaneous diseases of these species is necessary for ensuring animal welfare, as well as accurate interpretation and reporting of study findings. Working with avian and aquatic species can be especially challenging in this respect due to their rich diversity and array of unique adaptations. Here, we provide an overview of the research-relevant anatomic features, non-infectious conditions, and infectious diseases that impact research colonies of birds and aquatic animals, including fish and Xenopus species.

Nephroblastoma in a Common Mudpuppy Necturus maculosus simultaneously Present with a Mollicute Bacterium of the Genus Acholeplasma

In March 2017, a wild-caught female common mudpuppy Necturus maculosus from Iowa, USA, with an enlarged posterior abdomen was submitted for diagnostic assessment. The cause of the abdominal distension was a large fluid-filled abdominal mass, diagnosed as a nephroblastoma. Parasites and numerous bacteria were isolated and identified from the mudpuppy but were determined to be incidental. Samples of the neoplasm inoculated onto an American toad Anaxyrus americanus cell line (BufoTad) yielded cytopathic effect during several passages. However, standard molecular testing of the cell culture supernatant failed to identify any viruses. Next-generation sequencing identified the replicating agent as a bacterium of the genus Acholeplasma. Immunohistochemistry confirmed the presence of Acholeplasma within the nephroblastoma, including within tumor cells. This is the first report of nephroblastoma and the second report of neoplasia in this species. The results also suggest that certain bacteria of the genus Acholeplasma might be oncogenic.

Swim bladder tumors in the wavy medaka (Oryzias latipes)

Swim bladder tumors were detected in three out of 28 wavy medakas aged about 2 years old, all of which displayed abnormal swimming patterns caused by their spinal curvature. The tumors were located in the dorsal abdominal cavity. The swim bladder lumen was not detected in the region where it was originally assumed to be located, and that region was replaced with adipose tissue. The tumors were non-invasive, expansile, and encapsulated solid masses composed of a homogenous population of well-differentiated, densely packed, gas glandular epithelium-like cells. The tumor masses were connected to the rete mirabile, but the tumor cells did not infiltrate into them. Histopathologically, these tumors were diagnosed as adenomas originating from the gas glandular epithelium of the swim bladder. Spontaneous swim bladder tumors are rare in medaka, with an incidence of 0.02%; however, in the present study of wavy medaka, the incidence was much higher (10.7%). The long-term physical effects on the gas gland caused by swim bladder deformation considered to be a secondary effect of the spinal curvature may be an important factor in the proliferation of the gas glandular epithelium in the wavy medaka, resulting in the higher incidence of swim bladder tumors.

Testicular leiomyoma and spermatogenic failure syndrome in a seabass from broodstock

Testicular leiomyomas and gonadal dysfunctions are not commonly reported in teleost and particularly in broodstock fish. In the present work, a testicular leiomyoma related to an unusual case of spermatogenic failure syndrome, in a broodstock seabass coming from an Italian aquaculture farm, is reported. At gross pathology, the circumscribed neoplasia showed several white nodular masses, originating from the gonad, deforming the anatomo-physiological shape. From light microscopy, the presence of neoplastic tissue islands with spindle cells with a whirling pattern and the low presence of connective tissue were evident and originated from smooth muscle cells. Seminiferous tubules showed severe azoospermia with the absence of sperm cells even closer to the neoplastic area. Immunohistochemical analysis was positive for alpha-SMA, desmin and vimentin but negative for S-100, confirming a diagnosis of leiomyoma. This is the first report of spermatogenic failure syndrome associated with a testicular leiomyoma in fish from broodstock. More efforts should be made in studying broodstock fish pathologies related to fish maintenance and hormonal treatments that could economically affect aquaculture production.

Spontaneous neoplasia in captive syngnathid species: A retrospective case series (2003-2014) and literature review

Syngnathidae (seahorses, pipefish and seadragons) are charismatic species commonly kept in commercial aquaria, but published literature on syngnathid diseases is limited and immunohistochemical techniques not routinely employed. A retrospective review of 2,541 syngnathid submissions received between March 2003 and October 2016 identified 18 neoplasms including germ cell tumours, exocrine pancreatic and intestinal carcinomas, chromatophoromas, and single cases of lymphoma, thyroid and renal carcinoma, swim bladder and pituitary adenoma. Big-bellied seahorses accounted for 19% of submissions, but 50% of neoplasms were diagnosed in this species. This study includes the first reported cases of germ cell tumours, chromatophoroma, thyroid carcinoma and pituitary adenoma in Syngnathidae and the first reports of neoplasia in pipefish species. Out of nine commercial antibodies trialled for immunohistochemical characterization of neoplastic tissue, only pan-cytokeratin proved cross-reactive. Electron microscopy was performed in four cases. Tumours should be considered as differential diagnosis in cases with buoyancy issues, debilitated or emaciated animals, and may predispose to secondary infections. This study highlights the value of histopathological disease surveillance for commercial aquarium settings.

The ecology and evolution of wildlife cancers: Applications for management and conservation

Ecological and evolutionary concepts have been widely adopted to understand host-pathogen dynamics, and more recently, integrated into wildlife disease management. Cancer is a ubiquitous disease that affects most metazoan species; however, the role of oncogenic phenomena in eco-evolutionary processes and its implications for wildlife management and conservation remains undeveloped. Despite the pervasive nature of cancer across taxa, our ability to detect its occurrence, progression and prevalence in wildlife populations is constrained due to logistic and diagnostic limitations, which suggests that most cancers in the wild are unreported and understudied. Nevertheless, an increasing number of virus-associated and directly transmissible cancers in terrestrial and aquatic environments have been detected. Furthermore, anthropogenic activities and sudden environmental changes are increasingly associated with cancer incidence in wildlife. This highlights the need to upscale surveillance efforts, collection of critical data and developing novel approaches for studying the emergence and evolution of cancers in the wild. Here, we discuss the relevance of malignant cells as important agents of selection and offer a holistic framework to understand the interplay of ecological, epidemiological and evolutionary dynamics of cancer in wildlife. We use a directly transmissible cancer (devil facial tumour disease) as a model system to reveal the potential evolutionary dynamics and broader ecological effects of cancer epidemics in wildlife. We provide further examples of tumour-host interactions and trade-offs that may lead to changes in life histories, and epidemiological and population dynamics. Within this framework, we explore immunological strategies at the individual level as well as transgenerational adaptations at the population level. Then, we highlight the need to integrate multiple disciplines to undertake comparative cancer research at the human-domestic-wildlife interface and their environments. Finally, we suggest strategies for screening cancer incidence in wildlife and discuss how to integrate ecological and evolutionary concepts in the management of current and future cancer epizootics.

Malignant melanoma of brown bullhead (Ameiurus nebulosus) in Lake Memphremagog, Vermont/Quebec

In 2012, brown bullhead (Ameiurus nebulosus) with large, raised, black growths were first reported from multiple areas within the Vermont portion of Lake Memphremagog. Subsequent surveys conducted from 2014 to 2017 at two sites within the lake indicated a prevalence of 30% in adult brown bullhead 200 mm and above total length. These lesions ranged from slightly raised smooth black areas to large nodular areas on the body surface and fins and within the oral cavity. Microscopically, these lesions were determined to be malignant melanoma with invasion into surrounding hypodermis, skeletal muscle and bone as well as metastases to gill, ovary and intestine. Liver neoplasms were also observed in 8% of the bullhead collected from Lake Memphremagog in 2015. Neither skin nor liver neoplasms were noted in Ticklenaked Pond, a site used for comparison.

Genetic diversity, inbreeding and cancer

Genetic diversity is essential for adaptive capacities, providing organisms with the potential of successfully responding to intrinsic and extrinsic challenges. Although a clear reciprocal link between genetic diversity and resistance to parasites and pathogens has been established across taxa, the impact of loss of genetic diversity by inbreeding on the emergence and progression of non-communicable diseases, such as cancer, has been overlooked. Here we provide an overview of such associations and show that low genetic diversity and inbreeding associate with an increased risk of cancer in both humans and animals. Cancer being a multifaceted disease, loss of genetic diversity can directly (via accumulation of oncogenic homozygous mutations) and indirectly (via increased susceptibility to oncogenic pathogens) impact abnormal cell emergence and escape of immune surveillance. The observed link between reduced genetic diversity and cancer in wildlife may further imperil the long-term survival of numerous endangered species, highlighting the need to consider the impact of cancer in conservation biology. Finally, the somewhat incongruent data originating from human studies suggest that the association between genetic diversity and cancer development is multifactorial and may be tumour specific. Further studies are therefore crucial in order to elucidate the underpinnings of the interactions between genetic diversity, inbreeding and cancer.

Putative histiocytic sarcoma in redfin needlefish Strongylura notata (Beloniformes: Belonidae) in Florida, USA

Redfin needlefish Strongylura notata from Florida coastal waters were observed with unusual neoplastic lesions. Affected specimens were collected from 1 Atlantic estuary (Indian River Lagoon, prevalence = 0.32%, n = 5314) and 2 Gulf of Mexico estuaries (Tampa Bay, prevalence = 0.02%, n = 10762; Charlotte Harbor, prevalence = 0.02%, n = 5112) during routine fisheries-independent monitoring surveys conducted from 1999-2009. Grossly, each lesion manifested as a large (18-30 mm × 20-50 mm), raised (approximately 10 mm), white, creamy, or pinkish nodule on the flank, dorsal trunk, base of the pectoral fin, or head. Multiple small (<5 mm) nodules possessing poorly demarcated borders with neighboring tissues on the external jaw surface and at the base of the teeth were also observed. Histopathologically, neoplastic cells were found in the dermis, beneath the skeletal muscle, and in the soft tissue at the base of teeth of the premaxilla and the dentary jaw processes. Neoplastic cells usually had prominently invaded among the myosepta of the skeletal muscle. Neoplastic parenchymal cells had the basic characteristics of atypical, mononuclear, round, histiocytic cells with an eccentric, reniform nucleus and abundant cytoplasmic vacuolation, while some exhibited bizarre nuclear pleomorphism. Transmission electron microscopy revealed that neoplastic cells had a grooved nucleus and cytoplasmic organelles with rough endoplasmic reticulum, mitochondria, Golgi apparatus, and lysosomes. Neoplastic cells had possibly metastasized to liver, spleen, and kidney. Positive immunohistochemical staining with Ki67, p53, S-100, and CD163 support neoplastic features and a putative diagnosis of histiocytic sarcoma.

Cancer in wildlife: patterns of emergence

Cancer is ubiquitous in wildlife, affecting animals from bivalves to pachyderms and cetaceans. Reports of increasing frequency demonstrate that neoplasia is associated with substantial mortality in wildlife species. Anthropogenic activities and global weather changes are shaping new geographical limitations for many species, and alterations in living niches are associated with visible examples of genetic bottlenecks, toxin exposures, oncogenic pathogens, stress and immunosuppression, which can all contribute to cancers in wild species. Nations that devote resources to monitoring the health of wildlife often do so for human-centric reasons, including for the prediction of the potential for zoonotic disease, shared contaminants, chemicals and medications, and for observing the effect of exposure from crowding and loss of habitat. Given the increasing human footprint on land and in the sea, wildlife conservation should also become a more important motivating factor. Greater attention to the patterns of the emergence of wildlife cancer is imperative because growing numbers of species are existing at the interface between humans and the environment, making wildlife sentinels for both animal and human health. Therefore, monitoring wildlife cancers could offer interesting and novel insights into potentially unique non-age-related mechanisms of carcinogenesis across species.

Reversibility of Proliferative Thyroid Lesions Induced by Iodine Deficiency in a Laboratory Zebrafish Colony

A laboratory zebrafish colony developed red masses, predominantly under the jaw, in a significant portion of the population. The masses were diagnosed histopathologically as thyroid follicular hyperplasia, adenoma, or carcinoma in accordance with published morphologic criteria. After switching to a higher iodine brand of salt used to maintain a low level of salinity within the water system and a small diet change, the thyroid lesions regressed dramatically. Within 5 months the masses were no longer grossly visible. At the population level, external evaluations and histopathological assessments of whole-body sections document a regression in the prevalence of thyroid neoplasia and hyperplasia to normal thyroid conformation by 11 months after salt change. These findings suggest that a wide range of proliferative thyroid lesions, including neoplasms, in zebrafish may be hormone-dependent, even following lesion development. In addition, these results suggest that zebrafish have an adaptive ability to absorb iodine from water and food, which should be considered in discussions to standardize diets and when describing environmental parameters in publications.

Update on Cancer Treatment in Exotics

Treatment options for animals with cancer are rapidly expanding, including in exotic animal medicine. Limited information is available about treatment effects in exotic pet species beyond individual case reports. Most cancer treatment protocols in exotic animals are extrapolated from those described in humans, dogs, and cats. This review provides an update on cancer treatment in exotic animal species. The Exotic Species Cancer Research Alliance accumulates clinical cases in a central location with standardized clinical information, with resources to help clinicians find and enter their cases for the collective good of exotic clinicians and their patients.

Transmission of a common intestinal neoplasm in zebrafish by cohabitation

Intestinal neoplasms are common in zebrafish (Danio rerio) research facilities. These tumours are most often seen in older fish and are classified as small cell carcinomas or adenocarcinomas. Affected fish populations always contain subpopulations with preneoplastic lesions, characterized by epithelial hyperplasia or inflammation. Previous observations indicated that these tumours are unlikely caused by diet, water quality or genetic background, suggesting an infectious aetiology. We performed five transmission experiments by exposure of naïve fish to affected donor fish by cohabitation or exposure to tank effluent water. Intestinal lesions were observed in recipient fish in all exposure groups, including transmissions from previous recipient fish, and moribund fish exhibited a higher prevalence of neoplasms. We found a single 16S rRNA sequence, most similar to Mycoplasma penetrans, to be highly enriched in the donors and exposed recipients compared to unexposed control fish. We further tracked the presence of the Mycoplasma sp. using a targeted PCR test on individual dissected intestines or faeces or tank faeces. Original donor and exposed fish populations were positive for Mycoplasma, while corresponding unexposed control fish were negative. This study indicates an infectious aetiology for these transmissible tumours of zebrafish and suggests a possible candidate agent of a Mycoplasma species.

Tumours in white suckers from Lake Michigan tributaries: pathology and prevalence

The prevalence and histopathology of neoplastic lesions were assessed in white sucker Catostomus commersonii captured at two Lake Michigan Areas of Concern (AOCs), the Sheboygan River and Milwaukee Estuary. Findings were compared to those observed at two non-AOC sites, the Root and Kewaunee rivers. At each site, approximately 200 adult suckers were collected during their spawning migration. Raised skin lesions were observed at all sites and included discrete white spots, mucoid plaques on the body surface and fins and large papillomatous lesions on lips and body. Microscopically, hyperplasia, papilloma and squamous cell carcinoma were documented. Liver neoplasms were also observed at all sites and included both hepatocellular and biliary tumours. Based on land use, the Kewaunee River was the site least impacted by human activities previously associated with fish tumours and had significantly fewer liver neoplasms when compared to the other sites. The proportion of white suckers with liver tumours followed the same patterns as the proportion of urban land use in the watershed: the Milwaukee Estuary had the highest prevalence, followed by the Root, Sheboygan and Kewaunee rivers. The overall skin neoplasm (papilloma and carcinoma) prevalence did not follow the same pattern, although the percentage of white suckers with squamous cell carcinoma exhibited a similar relationship to land use. Testicular tumours (seminoma) were observed at both AOC sites but not at the non-AOC sites. Both skin and liver tumours were significantly and positively associated with age but not sex.

Fish Oncology: Diseases, Diagnostics, and Therapeutics

The scientific literature contains a wealth of information concerning spontaneous fish neoplasms, although ornamental fish oncology is still in its infancy. The occurrence of fish neoplasms has often been associated with oncogenic viruses and environmental insults, making them useful markers for environmental contaminants. The use of fish, including zebrafish, as models of human carcinogenesis has been developed and knowledge gained from these models may also be applied to ornamental fish, although more studies are required. This review summarizes information available about fish oncology pertaining to veterinary clinicians.

Cancer Prevalence and Etiology in Wild and Captive Animals

Neoplasia has been recorded in the vast majority of metazoans. The frequent occurrence of cancer in multicellular organisms suggests that neoplasia, similar to pathogens/parasites, may have a significant negative impact on host fitness in the wild. This is supported by the fact that wildlife cancers have recently been shown to result in significantly increased levels of mortality and concomitant reduction in fitness. By thorough searches of the available literature we provide a comprehensive and an updated list of cancer prevalence and etiology in the wild. We were, however, unable to find data on nontransmissible cancer prevalence in invertebrates and consequently this chapter focuses on cancer in wild vertebrates. Although single cases of cancer are frequently encountered in the wildlife, we were only able to retrieve robust data on cancer prevalence for 31 vertebrate species (12 fish, 3 amphibians, 2 reptiles, 2 birds, and 12 mammals). Cancer prevalence among these vertebrates ranged from as low as 0.2% observed in Canada geese (Branta canadensis) to more than 50% recorded in both Santa Catalina Island foxes (Urocyon littoralis catalinae) and Cape mountain zebras (Equus zebra zebra). The high prevalence recorded in some vertebrates strongly suggests that cancer in wildlife may indeed carry significant fitness costs. In spite of this, the low number of published comprehensive studies clearly shows that so far cancer in wildlife has received insufficient attention by biologists. We hope that this chapter will act as a catalyst for further studies focusing on the impact of cancer in wild animals. The chapter additionally compares cancer recorded in French zoological parks to those obtained at other zoological parks. Finally, we provide an updated list of cancer recorded as single cases in the wild, as well as in captive animals.

Anatomy and Disorders of the Oral Cavity of Ornamental Fish

Ornamental fish represent the largest and most diverse group of exotic animals kept as pets. The specific oral anatomy of each family or selected species has evolved to suit the natural environment, feeding behaviors, food or prey type, and location of the food/prey in the water column. The anatomy can change over the life of the animal, from fry to adult. The oral cavity of fish is susceptible to many problems including infectious and parasitic diseases, trauma, and neoplasia. Diagnosis may involve wet mount preparations of exfoliative cytology from the lesion, histopathology, and bacterial or fungal culture.

Hernia of the swim bladder (aerocystocele) with concurrent mycotic granulomatous inflammation and swim bladder carcinoma in a wild mullet (Mugil cephalus)

We describe a hernia of the swim bladder, with a concurrent mycotic granulomatous inflammation, and carcinoma of the swim bladder in a wild mullet (Mugil cephalus) referred for an exophytic dorsal mass. Grossly, the mass was white, soft, and composed of multiple cystic gas-containing chambers connected by a funnel-shaped tissue segment to the coelomic swim bladder. Histologically, the mass was characterized by cysts of variable size, multifocally contiguous with the subepithelial rete mirabile, supported by abundant fibrous tissue. The skin covering the herniated swim bladder was focally ulcerated and replaced by abundant granulation tissue in which multiple scattered granulomas centered on pigmented fungal hyphae were observed. These granulomas were also seen in the remaining coelomic portion of the swim bladder as well as in the spleen, perivisceral pancreas, and peritoneal adipose tissue; the fungus was molecularly identified as Cladosporium spp. Focally, arising from the herniated swim bladder epithelium, an unencapsulated poorly demarcated, moderately cellular neoplasm, composed of islands, lobules, and acini of neoplastic epithelium, was found.

Endogenous Retroviruses in Fish Genomes: From Relics of Past Infections to Evolutionary Innovations?

The increasing availability of fish genome sequences has allowed to gain new insights into the diversity and host distribution of retroviruses in fish and other vertebrates. This distribution can be assessed through the identification and analysis of endogenous retroviruses, which are proviral remnants of past infections integrated in genomes. Retroviral sequences are probably important for evolution through their ability to induce rearrangements and to contribute regulatory and coding sequences; they may also protect their host against new infections. We argue that the current mass of genome sequences will soon strongly improve our understanding of retrovirus diversity and evolution in aquatic animals, with the identification of new/re-emerging elements and host resistance genes that restrict their infectivity.

Risk factors for development of internal neoplasms in koi carp Cyprinus carpio koi

Fish, like mammals, can be affected by neoplastic proliferations. As yet, there are only a very small number of studies reporting on the occurrence of tumours in koi carp Cyprinus carpio koi and only sporadic reports on the nature of the tumours or on risk factors associated with their development. Between 2008 and 2012, koi with abdominal swelling were examined pathologically: neoplastic lesions were diagnosed and classified histologically. We evaluated possible risk factors for the development of these internal neoplasms in koi carp in Switzerland, using an online 2-part questionnaire sent to fish keepers with koi affected by internal tumours and to fish keepers who had not previously reported any affected koi. Part 1 addressed all participants and focused on general information about koi husbandry and pond technical data; Part 2 addressed participants that had one or several case(s) of koi with internal tumour(s) between 2008 and 2012, and consisted of specific questions about affected koi. A total of 112 internal tumours were reported by the 353 koi keepers participating in the survey. Analysis of the obtained data revealed that tumour occurrence was significantly associated with the location (indoors vs. outdoors) and volume of the pond, frequency of water changes, origin of the koi, number of koi kept in a pond and the use of certain pond disinfectant/medication products. Our results contribute to the identification of possible risk factors, which in turn could help to establish prophylactic measures in order to reduce the occurrence of internal neoplasms in koi.

A novel investigation of a blister-like syndrome in aquarium Echinopora lamellosa

This study investigates potential causes of a novel blister-like syndrome in the plating coral Echinopora lamellosa. Visual inspections of this novel coral syndrome showed no obvious signs of macroparasites and the blisters themselves manifested as fluid-filled sacs on the surface of the coral, which rose from the coenosarc between the coral polyps. Histological analysis of the blisters showed that there was no associated necrosis with the epidermal or gastrodermal tissues. The only difference between blistered areas and apparently healthy tissues was the presence of proliferated growth (possible mucosal cell hyperplasia) directly at the blister interface (area between where the edge of the blister joined apparently healthy tissue). No bacterial aggregates were identified in any histological samples, nor any sign of tissue necrosis identified. We conclude, that the blister formations are not apparently caused by a specific microbial infection, but instead may be the result of irritation following growth anomalies of the epidermis. However, future work should be conducted to search for other potential casual agents, including viruses.