Tumours and microbial diseases of marine fishes in Alaskan waters

Abstract. In an effort further to define the current health status of demersal fish in the Bering Sea, 36 618 fish captured by otter trawl during 1976 were examined for pathological conditions. Of the 26 species examined, 22 were found to have no detectable abnormalities. The four species with abnormalities were Pacific cod Gadus macrocephalus Tilesius with pseudobranchial tumours and skin lesions, walleye pollock Theragra chalcogramma (Pallas) with pseudobranchial tumours, yellowfin sole Limanda aspera (Pallas) with lymphocystis, and rock sole Lepidopsetta bilineata (Ayres) with epidermal papillomas. The prevalence, geographical distribution and biological and pathological characteristics of affected individuals were determined.
Pseudobranchial tumours of both Pacific cod and walleye pollock were occasionally found to be invasive. Fish bearing these tumours were distributed throughout the sampling area. The epidermal papillomas on rock sole resembled similar tumours found on several flatfish species along the West Coast of North America. The distribution of this disease appeared to be depth related. The virus-caused lymphocystis growths were located on the 'blind' side of yellowfin sole. The highest frequencies of fish with lymphocystis were in the south-eastern Bering Sea. Two main types of skin lesions were seen on Pacific cod: ulcers and ring-shaped lesions. Isolates of bacteria ( Pseudomonas sp.) were routinely obtained from the cod ulcers and may be the cause of this disease. The ring-shaped skin lesions, when examined microscopically, contained unidentified epidermal basophilic bodies.     

Lesions associated with natural and experimental infections of Aeromonas hydrophila in channel catfish, Ictalurus punctatus (Rafinesque)

Abstract. Histologic differences were observed in channel catfish, Ictalurus punctatus (Rafinesque), with naturally occurring cutaneous (bacteria isolated only from lesions of skin and superficial muscle) and systemic Aeromonas hydrophila infections. Systemic infections were characterized by diffuse necrosis in several internal organs and the presence of melanin-containing macrophages in the blood. Fish with only cutaneous infections had several types of concealed lesions including increased amounts of lipofuscin and haemosiderin in the liver and spleen; however, most visceral organs were not necrotic. The average condition factor of fish with cutaneous infections was lower than for fish with systemic infections. Early histologic lesions in channel catfish experimentally infected by immersion in a suspension of A. hydrophila were similar to lesions observed in naturally occurring systemic infections and to lesions previously reported in channel catfish injected intraperitoneally with A. hydrophila . In experimentally infected fish, all lesions healed in fish that did not die, and prolonged infections limited to skin and muscle did not occur.     

Morphopathological features of a severe ulcerative disease outbreak associated with Tenacibaculum maritimum in cultivated sole, Solea senegalensis (L.)

This study describes morphopathologic changes in naturally infected farmed Senegalese sole affected by tenacibaculosis caused by Tenacibaculum maritimum. Macroscopic observation, in addition to light microscopy and scanning electron microscopy, was used to study the lesions. Main lesions were characterized by complete loss of epidermis and dermis, as well as extensive necrosis of muscle layers. Mild-to-moderate inflammatory response with the presence of macrophages was noted around hyaline degenerated muscle cells. Gram-negative filamentous bacteria could be detected only at the dermis. Under scanning electron microscopy, filamentous bacteria located over the scales without epithelium could be observed. These findings together with the isolation and PCR detection of the bacteria in kidney and skin tissues suggest that once the bacteria reach the dermis, probably through eroded epidermis, they are able to proliferate and produce enzymes that are responsible for the damage in the underlying tissues.     

The importance of Lernaea cruciata (Le Sueur) in the initiation of skin lesions in largemouth bass, Micropterus salmoides (Lacepede), in the Chowan River, North Carolina, USA

Abstract. Largemouth bass, Micropterus salmoides (Lacepede), were collected from May to October from the Chowan River, North Carolina and examined for the presence of skin lesions. Over 55% of all largemouth bass greater than 100 mm in length had skin lesions. The largest fish (≥400 mm) had the greatest number of lesions (= 3.4 lesions per fish). When examined by wet mounts, small early lesions frequently (31% of all lesions) had the microscopic recently metamorphosed adult female stage of Lernaea cruciata . Older macroscopically visible adult females were only rarely seen (2% of all lesions). Examinations of wet mounts revealed no identifiable pathogen in 60% of all early lesions but histologically almost all lesions had a similar inflammatory response. Lesions were most common along the ventral surface of the body where 85% of all lesions were present. This was also the most common site of copepod infection, with 95% of all copepods present at this site. Bacterial numbers in early lesions were occasionally high and tended to increase in concentration in advanced lesions. No single organism was consistently identified as predominant in the majority of lesions. The possible relationship of these lesions to red-sore disease is discussed.     

Cephalic osteochondritis and necrotic scleritis in intensively reared salmonids associated with Flexibacter psychrophilus

Three cases of pyogranulomatous cephalic osteochrondritis of intensively reared rainbow trout, Oncorhynchus mykiss (Walbaum), and Atlantic salmon, Salmo salar L., in Canada and Chile, respectively, were examined for histopathological and bacteriological changes, and by using immunohistochemistry. Bilateral exophthalmia and intraocular haemorrhage were the most common gross lesions seen in the Ontario fish. Histologically, the major pathological changes seen in all cases involved the developing bone and cartilage of the head region, including the eye. Necrosis and pyogranulomatous inflammation of the scleral cartilage (necrotic scleritis) were the major ocular changes. Similarly, lysis of cephalic cartilage and immature bone, accompanied by pyogranulomatous inflammation, usually progressing to fibrosis, were the most common lesions associated with the cranial changes in both the rainbow trout and Atlantic salmon. Routine histological staining, including special stains, failed to reveal the presence of pathogens associated with these lesions. However, immunohistochemical staining of representative sections from all cases with rabbit anti- Flexibacter psychrophilus serum (ATCC 49510) demonstrated significant numbers of antigenically related bacteria within the leading edge of some of the scleral and cephalic osteochondritic lesions. Axenic cultures of Flexibacter psychrophilus were recovered from the eye lesions of the rainbow trout, but it was not possible to reproduce ocular lesions experimentally. However, mortality was produced following intramuscular injection of rainbow trout with bacteria.     

Puffy skin disease (PSD) in rainbow trout,Oncorhynchus mykiss (Walbaum): a case definition

Puffy skin disease (PSD) is a disease that causes skin pathology in rainbow trout, Oncorhynchus mykiss (Walbaum). Incidence of PSD in UK fish farms and fisheries has increased sharply in the last decade, with growing concern from both industry sectors. This paper provides the first comprehensive case definition of PSD, combining clinical and pathological observations of diseased rainbow trout from both fish farms and fisheries. The defining features of PSD, as summarized in the case definition, were focal lateral flank skin lesions that appeared as cutaneous swelling with pigment loss and petechiae. These were associated with lethargy, poor body condition, inappetance and low level mortality. Epidermal hyperplasia and spongiosis, oedema of the dermis stratum spongiosum and a mild diffuse inflammatory cellularity were typical in histopathology of skin. A specific pathogen or aetiology was not identified. Prevalence and severity of skin lesions was greatest during late summer and autumn, with the highest prevalence being 95%. Atypical lesions seen in winter and spring were suggestive of clinical resolution. PSD holds important implications for both trout aquaculture and still water trout fisheries. This case definition will aid future diagnosis, help avoid confusion with other skin conditions and promote prompt and consistent reporting.     

The prevalence of mycobacterial infections in striped bass in Chesapeake Bay

Several species of bacteria have been isolated from diseased striped bass, Morone saxatilis (Walbaum), in Chesapeake Bay. Mycobacteria species are of particular interest because of their association with chronic lesions in both fish and humans. The resulting disease in fish may be characterised by emaciation, inflammation of the skin, exophthalmia (pop‐eye), ascites (dropsy), open lesions, and ulceration. The prevalence of mycobacterial infection in 217 striped bass in the Maryland portion of Chesapeake Bay was determined to provide evidence of decreased overall condition of fish affected by these bacteria. The density of the granulomas was higher in the spleen and head kidney than either the heart or liver, and appeared to be most closely associated with the presence of an external lesion. Thirty‐eight per cent of the fish showed some sign of an external lesion. Granulomas appeared in at least one organ in 53% of the fish sampled regardless of the presence or absence of an external skin lesion. Condition factor was significantly higher for striped bass without external lesions (0.96) than those with lesions (0.82). Striped bass with no internal granulomas and no external lesion had the highest condition factor (0.99) and fish with granulomas and external lesions the lowest (0.81). Slopes of the regression log_e weight (g) and log_e length (mm) for striped bass with external lesions was significantly higher than those fish without external lesions and had a lower r². The results suggest that striped bass that are infected with mycobacteria have decreased overall health.     

Parasites and hepatic lesions among pink salmon, Oncorhynchus gorbuscha (Walbaum), during early seawater residence

Juvenile pink salmon, Oncorhynchus gorbuscha (Walbaum), in the Broughton Archipelago region of western Canada were surveyed over 2 years for sea lice (Lepeophtheirus salmonis and Caligus clemensi), gross and microscopic lesions and evidence of infections with viruses and bacteria. The 1071 fish examined had an approximate ocean residence time no longer than 3 months. A high prevalence of degenerative liver lesions, renal myxosporean parasites and a low prevalence of skin lesions and sea lice were observed. No indications of viral or bacterial diseases were detected in either year. The monthly prevalence of sea lice in 2007 (18-51%) was higher than in 2008 (1-26%), and the infestation density exceeded the lethal threshold in only two fish. Degenerative hepatic lesions and renal myxosporean parasites occurred in approximately 40% of the pink salmon examined in June of both years, and the peak monthly prevalence of hepatocellular hydropic degeneration was greater in 2007 (32%, in May) than in 2008 (12%, in June). Logistic regression analysis found skin lesions and hepatocellular hydropic degeneration significantly associated with sea lice. Most parasites and lesions occurred during both years, but the prevalence was often higher in 2007. Fish weight was 35% less in June 2007 than in June 2008, but condition factor was not different. Further research is required to monitor inter-annual variations and aetiology of the liver lesions and to assess their potential role on pink salmon survival.     

Pathology of Enterococcus sp. infection in farmed turbot, Scophthalmus maximus L.

Abstract The lesions of an enterococcal septicaemia occurring in turbot, Scophthalmus maximus (L.), cultured in several farms in northwest Spain are described. The agent of this septicaemia was identified previously as an Enterococcus -like bacterium. Two main patterns of lesions were observed in the diseased turbot: a focal form characterized by exophthalmia, muscular haemorrhages, acute branchitis, and suppurative inflammation of periorbital tissues, eyeball, meninges and brain; and another generalized form with similar lesions, but showing more extensive haemorrhages, ulceration and purulent inflammation of the skin, desquamative enteritis, and necrosis of spleen and kidney. Fatty changes of the liver were observed in all turbot examined (diseased and controls), which indicates that these alterations were not related to the infection. Experimentally inoculated turbot developed lesions corresponding to the generalized form of the natural disease. Although the Enterococcus strain was recovered in pure culture from all the organs, Gram-positive bacteria could not be visualized histologically in the lesions of muscle and brain.     

Ulcerative dermatitis in wild dusky grouper Epinephelus marginatus (Lowe) from Libyan waters

In the period 2013–2015, wild dusky grouper, Epinephelus marginatus (Lowe), caught in Libyan coastal waters and ranging in size from 42 to 92 cm in total length, were observed to have distinctive skin lesions of unknown aetiology. Histopathologically, the lesions comprised a multifocal, unilateral or bilateral dermatitis, involving the epidermis, superficial dermis and scale pockets, and sometimes, in severe cases, the hypodermis. Severe lesions had marked epidermal spongiosis progressing to ulceration. Healing was observed in some fish. Bacteria and fungi could be isolated from severe lesions, although they were not seen histopathologically in early‐stage lesions. By contrast, metazoan parasite eggs were observed in the dermis and epidermis of some fish with mild and moderate dermatitis. Unidentified gravid digenean trematode parasites carrying similar eggs were also seen within the blood vessels of the deep and superficial dermis. The cause of this distinctive condition, termed dusky grouper dermatitis (DGD), and its potential impact upon already threatened Mediterranean wild dusky grouper populations and upon cultured grouper more widely have yet to be established.     

Aeromonas sobria, a causative agent of disease in farmed perch, Perca fluviatilis L

Significant numbers of perch, Perca fluviatilis, raised on a pilot fish farm in Switzerland presented focal skin lesions on the lateral sides and fin rot. Mortality rates reached levels of up to 1% of the total fish on the farm per day. Virtually pure cultures of Aeromonas sobria were isolated from the liver, kidney, spleen and skin lesions of affected fish. Aeromonas sobria isolated from the farmed perch had a haemolytic effect on sheep and trout erythrocytes, autoaggregated, was cytotoxic for cultured fish cells and possessed genes involved in type III protein secretion. Experimental infection of naive perch with a single colony isolate of A. sobria from an affected farm fish resulted in the development of clinical signs identical to those seen on the farm. The results indicate that A. sobria can act as a primary pathogen of perch.     

Scanning Electron Microscopy of “Saddleback” Lesions Associated with Experimental Infections of Flavobacterium columnare in Channel Catfish,Ictalurus punctatus (Siluriformes: Ictaluridae), and Zebrafish,Danio rerio (Cypriniformes: Cyprinidae)

Laboratory‐reared, specific pathogen‐free fingerling channel catfish, Ictalurus punctatus, and adult zebrafish, Danio rerio, were each separately exposed by immersion challenge to the etiological agent of “columnaris disease,”Flavobacterium columnare (Japanese Collection of Microorganisms 21327 strain). At 24‐h post‐immersion, fish exhibiting a “saddleback” lesion were fixed whole in 10% neutral buffered formalin. Skin samples approximately 5 mm² were excised from both the margin and center of each saddleback lesion as well as from corresponding sites in control, non‐challenged, fish before being prepared routinely for scanning electron microscopy (SEM). Skin samples from control channel catfish and zebrafish had uniform, contiguous epidermal cells with continuous or closely apposed cell margins and well‐defined microridges. Channel catfish skin lesion samples had margins typified by epidermal sloughing and lesion centers that exhibited a multitude of rod‐shaped bacterial cells, approximately 3–10 µm long × 0.3–0.5 µm wide, intermingled with cellular debris across a surface characterized by denuded, strongly ridged, or folded dermal connective tissue. Zebrafish skin lesion samples had a multitude of rod‐shaped bacterial cells and exhibited comparable ultrastructural changes but some lacked scales. These findings are the first published SEM observations of columnaris disease and saddleback lesions in channel catfish and zebrafish and thereby advance our understanding of the ultrastructural characteristics of acute‐stage saddleback lesions and columnaris disease pathogenesis.     

Analysis of the composition of the bacterial community in puffer fish Takifugu obscurus

The food chain has been postulated as one pathway for tetrodotoxin (TTX)-producing bacteria to enter into fish. However, the background composition of the bacterial community in puffer fish is unclear. Using 16S rDNA PCR denaturing gradient gel electrophoresis (PCR-DGGE) technology, we investigated the composition of bacterial communities in the skin, intestines, and TTX-accumulating organs (ovary, liver) of the striped puffer fish Takifugu obscurus. A total of 38 species of different culture-independent bacteria were isolated and classified according to phylogenetic analysis. Of these species, those belonging to the class γ-Proteobacteria dominated the microbial community in the puffer fish, while others belonged to the group of low DNA G + C content, Cytophaga–Flavobacterium–Bacteroides (CFB) group, α-Proteobacteria, β-Proteobacteria, ε-Proteobacteria and Spirochaetales. Gram positive bacteria of the group of low DNA G + C content were seen as the dominant component in the intestine, while γ-Proteobacteria was the dominant group in the skin or TTX-accumulating organs. The TTX-accumulating organs were found to contain bacteria from all TTX-producing genera reported previously. We also observed large differences in the bacterial assemblages in the intestines of fish fed natural and artificial diets.     

Infection experiments with Aphanomyces invadans in four species of estuarine fish

Along the eastern seaboard of the US, Atlantic menhaden, Brevoortia tyrannus, develop characteristic ulcerative lesions, a condition termed ulcerative mycosis. These lesions are identical to those seen across Asia in fish affected by epizootic ulcerative syndrome, a condition caused by the fungus-like oomycete Aphanomyces invadans. Young-of-the-year menhaden inhabiting estuarine environments are the primary species affected in the USA and little is known about the factors involved in the initiation of the lesions, or why menhaden are predominantly infected. Atlantic menhaden, hogchoker, Trinectus maculatus, striped killifish, Fundulus majalis, and mummichog, Fundulus heteroclitus, were inoculated with A. invadans (80 zoospores per fish) to explore species differences in infection and lesion development. All four species developed lesions. Killifish developed frank lesions similar to those observed in menhaden but the gross lesions occurred later, approximately 5-10 days after those on menhaden. Hogchoker and mummichog did not develop gross skin ulcers; rather, their lesions appeared as reddened areas under the epidermis. Mummichogs also showed evidence of significant healing with a well-developed granuloma and significant myocyte regeneration. These experiments show that species barriers as well as ecological barriers can explain some of the factors involved in the development of lesions in, and specificity of the water mould for, menhaden.     

Risk factors for skin lesions in Atlantic salmon, Salmo salar L.

Risk factors for skin lesions observed on the slaughter line in Atlantic salmon, Salmo salar L., were examined in a cohort study in Hordaland County, Norway. The salmon were followed from seawater introduction, starting in April 1994, until the last group was slaughtered in February 1996. The findings indicated that the egg and smolt stages were important factors in the prevalence of skin lesions at slaughter. There appeared to be differences in the risk for skin lesions between salmon from different egg suppliers to the smolt farms. An increase of 3 months between vaccination and seawater introduction increased the relative risk (RR) for skin lesions (RR = 1.9). Salmon vaccinated with a vaccine with adjuvants derived from plant oil appeared to be at higher risk for skin lesions (RR = 4.6) than those vaccinated with a vaccine with adjuvants derived from mineral oil (RR = 1.4). The larger the salmon (from 3.1 to 5.7 kg), the lower the risk for skin lesions (RR = 0.4).     

Skin pathology in Hawaiian goldring surgeonfish,Ctenochaetus strigosus (Bennett)

Twenty‐eight goldring surgeonfish, Ctenochaetus strigosus (Bennett), manifesting skin lesions and originating from the north‐western and main Hawaiian Islands were examined. Skin lesions were amorphous and ranged from simple dark or light discolouration to multicoloured tan to white sessile masses with an undulant surface. Skin lesions covered 2–66% of the fish surface, and there was no predilection for lesions affecting a particular part of the fish. Males appeared over‐represented. Microscopy revealed the skin lesions to be hyperplasia, melanophoromas or iridophoromas. The presence of skin tumours in a relatively unspoiled area of Hawaii is intriguing. Explaining their distribution, cause and impact on survivorship of fish all merit further study because C. strigosus is an economically important fish in the region.     

Phenotypical and genotypical characterization of Shewanella putrefaciens strains isolated from diseased freshwater fish

Between 2007 and 2012, a variety of disease outbreaks most often characterized by skin disorders were observed among different species of freshwater fish in Poland. In most cases, the clinical signs included focally necrotized gills, necrotic skin lesions or ulcers. Internally, haemorrhages, oedematous kidney and abnormal spleen enlargement were generally noted. The disorders were accompanied by increased mortality. Most of the problems concerned cultured common carp Cyprinus carpio L. and rainbow trout Oncorhynchus mykiss (Walbaum). Fish have been examined from a number of these farms, and additionally, the wild and ornamental fish with similar clinical signs of diseases were also tested. Bacteria were isolated consistently from lesions and internal organs. They had characteristic orange-pigmented colonies which grew in pure culture or constituted 55–95% of total bacterial flora. One hundred and eighteen isolates were collected and biochemically identified as Shewanella putrefaciens group, and this was confirmed by sequencing. Challenge tests confirmed the pathogenicity of these bacteria. This is the first report characterizing and describing S. putrefaciens as a pathogen of different species of freshwater fish in Europe.     

The pathology of chronic erosive dermatopathy in Murray cod, Maccullochella peelii peelii (Mitchell)

Chronic erosive dermatopathy (CED) is a disease of intensively farmed Murray cod in Australia that has been reported in association with the use of groundwater (mechanically extracted from shallow boreholes) supplies. CED results in focal ulceration of the skin overlying sensory canals of the head and flanks. Trials were conducted at an affected fish farm to study the development of the condition, both in Murray cod and in goldfish, and also to assess the reported recovery of lesions when affected fish were transferred to river water. Grossly, lesions began after 2-3 weeks with degeneration of tissue at the periphery of pores communicating with the sensory canals. Widening of these pores along the axis of the canals resulted from a loss of tissue covering the canal. Histopathologically, hyperplasia of the canal epithelial lining was seen after 3 weeks in borehole water and subsequent necrosis and sloughing of this tissue resulted in the loss of the canal roof. Canal regeneration occurred when fish were transferred from borehole water into river water. The lack of lesions in other organs and the pattern of lesion development support exposure to waterborne factors as the most likely aetiology.     

Spontaneous melanotic lesions in axillary seabream,Pagellus acarne (Risso)

In this article, we describe spontaneous melanotic lesions in the skin of axillary seabream, Pagellus acarne (Risso), from a defined area of the Portuguese Coast, located in Cabo da Roca and Foz do Arelho. The lesions corresponded to the black pigmentation spots on the skin of the head, fins, lips and conjunctiva and, additionally, black nodules on the skin of the head and lips. In some specimens, the nodular formations in the head changed their anatomical conformation. Histologically, there were melanophores scattered along the basement membrane or forming aggregates in the dermis, infiltrating the subcutaneous tissue but not invading the adjacent muscle tissue. The aim of this study was to characterize the macroscopic and microscopic features of the pigmented lesions. These fish show sessile hyperpigmented lesions (spots) that correspond to proliferative lesions of melanophores in the dermis and nodular lesions that correspond to neoplastic lesions, melanophoromas. The melanophores in such lesions showed high concentration of melanin in the cytoplasm, moderate pleomorphism and compact distribution throughout all of the dermis.     

Histopathology and prevalence of epidermal papillomas epidemic in brown bullhead, Ictalurus nebulosus (Lesueur), and white sucker, Catostomus commersoni (Lacépède), populations from Ontario, Canada

Abstract. White sucker, Catostomus commersoni (Lacépède), and brown bullhead, Ictalurus nebulosus (Lesueur), populations throughout the Great Lakes examined for evidence of pollution associated neoplasia exhibited a variety of morphologically distinct skin lesions. Three types of skin lesions affected white suckers: (a) focal on the lips, (b) discrete on the body, or (c) raised mucoid focal lesions on the skin and fins. Histologically, all three types featured a continuum between mild epidermal hyperplasia and benign papillomata. Brown bullheads exhibited a single variably shaped raised lesion on all body surfaces and within the oral cavity in addition to focal lip lesions. All bullhead lesions exhibited a continuum between mild epithelial hyperplasia and papillomata. Some skin lesions in both species were invasive but most abnormalities represented some stage in the development of epidermal papillomas. These papillomas superficially resemble papillomas common in many fish species and which are associated with viruses, but sucker and bullhead papillomas exhibit a unique range of histopathological and gross morphological appearances. The high prevalence of these papillomas, affecting up to 60% of some populations in polluted areas, supports the possibility that carcinogenic chemicals in the sediments are influencing papilloma development.