Myxosporean infection causing intestinal disease in farmed turbot, Scophthalmus maximus (L.), (Teleostei: Scophthalmidae)

The present report describes an intestinal disease which causes important losses in farmed turbot. Mortality rates were higher in summer and reached 100% in all tanks where the disease was confirmed. Affected fish showed external signs consisting of anorexia, sunken eyes and a typical prominent bony ridge on the skull. These signs can be considered the pathognomonic signs of the disease, together with the gut lesions seen in the histological study. Pallor of the internal organs, intestinal haemorrhages and the presence of liquid in the intestine were also observed, with ascites in heavily infected fish. Histopathological damage was evident in the gut, with severe enteritis, detachment of epithelium, haemorrhages and inflammation of the subepithelial connective tissue. The myxosporean aetiology was demonstrated in all the fish showing the characteristic signs of disease. Myxosporean stages, including scarce spores, were found in the affected epithelium or free in the intestinal lumen together with epithelial debris. The present study demonstrates the importance of this myxosporean disease which represents a serious threat for turbot culture. This is also the first record of a member of the Myxosporea in turbot.     

The clinical diagnosis of protozoal myositis syndrome (Neospora caninum) of puppies

Nine puppies suffered from progressive paresis with muscle wasting, hyporeflexia and extensor rigidity. CK-activity in serum was elevated and electrodiagnostic findings were indicative of lower motor neuron disease. Although lesions were also found in the CNS, additional neurological signs were rare, but CSF examination revealed the presence of inflammatory lesions. On pathologic examination, all animals had a disseminated necrotizing myositis. In addition, a disseminated encephalomyelitis was found as well as, in 2 cases, a neuritis. In the lesions of 6 animals protozoal organisms were found which were immunocytochemically identified as Neospora caninum. Our results show that the protozoal myositis-encephalitis syndrome in puppies can be diagnosed in the clinic with high probability. A clinical differentiation between toxoplasmosis and Neospora caninum infection is presently difficult.     

Proliferative kidney disease: first reported outbreak in North America

Abstract. Proliferative kidney disease (PKD) was diagnosed in rainbow trout, Salmo gairdneri Richardson, at the Hagerman, Idaho, State Fish Hatchery. Wild fish from Riley Creek, one of the hatchery water supplies, were infected with PKD organisms. Clinical signs, gross pathology and histopathology of affected fish were typical of those reported for PKD in salmonids from European hatcheries. In addition to lesions normally seen, we observed a severe vasculitis and occlusion of renal and hepatic vessels. Ultrastructure of the PKD organism and possible inclusion body production sites are described. The disease outbreak was complicated by the presence of other infectious diseases. This is the first recorded outbreak of PKD in North America.     

Fusarium incarnatum isolated from black tiger shrimp, Penaeus monodon Fabricius, with black gill disease cultured in Vietnam

Fusarium incarnatum was isolated from gill lesions of cultured black tiger shrimp, Penaeus monodon, in every crop during 2000-2002 in Nghe An province, Vietnam. Infected shrimps showed typical signs of black gill disease and mortalities about a month prior to harvest. Detailed morphological examinations, as well as molecular phylogenic analyses based on partial nucleotide sequences of ribosomal DNA, were made on the isolates. An artificial infection of kuruma prawn, Penaeus japonicus, using two selected isolates was also conducted and their pathogenicity determined.     

Streptococcosis in cultured turbot, Scopthalmus maximus (L.), associated with Streptococcus parauberis

Several strains of Garm-positive short rod (coccibacilli)-shaped bacteria were isolated from diseased cultured turbot, Scophthalmus maximus (L.), in the North of Spain with lesions and signs of Spain with lesions and signs of streptocecosis. The α-haemolytic streptoceoccus-like organisms from diseased turbot were identified by physiological, biochemical and 16S rRNA gene sequence analysis as Streptococcus parauberis. This is the first report of S. parauberis associated with fish disease.     

Pathology of shell disease in the blue crab, Callinectes sapidus Rathbun, (Decapoda: Portunidae)

Blue crabs affected with shell disease displayed a wide array of pathologies in response to this very common affliction. Grossly, shell disease lesions most commonly presented as variably sized brown to black foci. Such lesions ranged from very small (1 mm2) to locally extensive (up to 200 mm2 in area). The larger of the melanized lesions sometimes appeared ulcerated. The most severe lesions observed (Pamlico River shell disease-PRSD) resulted in loss of up to 25% of the entire carapace. A diverse bacterial flora consisting of aeromonads, vibrios and five other genera were isolated as the predominant organisms from shell disease lesions. Fungi were rarely observed in larger lesions. Protozoa and algae were also rarely observed on the surface of some lesions. Histologically, lesions ranged from mild erosion of the epicuticle and outermost layers of the calcified endocuticle to more extensive endocuticle erosion with accompanying inflammation. In the most severe cases, there was total loss of the endocuticle and epidermis, with pseudomembrane formation, intense haemocyte infiltration, and involvement of adjacent viscera. There was no apparent relationship between the size of gross lesions and their histological severity (as defined by the extent of tissue damage), suggesting that gross examination of shell disease lesions is not a reliable method for assessing the damage to affected blue crabs.     

Acid water and aluminium exposure: gill lesions and aluminium accumulation in farmed brown trout, Salmo trutta L.

Abstract. Brown trout, Salmo trittta L., from two fish farms, situated within acid-susceptible areas in Sweden, were studied with respect to aluminium accumulation and gill pathology. The total aluminium concentrations, after liming of the water in both farms, were between 200 and 300μg/1 at sampling. Brown trout from a third farm in a non-acidified area (total aluminium concentration of water 35μg/1 were included as a control. The aluminium concentrations in gills from farmed brown trout in acidified areas were approximately 20μg/g and 90μg/g wet weight respectively compared with approximately 2μg/g wet weight in control brown trout gills. Light- and electron microscopic examination disclosed two major types of gill lesions characterized by chloride cell hyperplasia in the secondary lamellar epithelium and enlargement of the intercellular spaces in the secondary lamellar epithelium. The difference in the aluminium speciation and accumulation may explain the difference in the gill pathology of farmed fish from acidified areas. The chloride cell hyperplasia together with a relatively low aluminium accumulation is considered to reflect a long-term exposure effect.     

Longitudinal study of a natural outbreak of heart and skeletal muscle inflammation in Atlantic salmon, Salmo salar L

Heart and skeletal muscle inflammation (HSMI) is a transmissible disease of farmed Atlantic salmon, Salmo salar L. It is characterized by significant epi-, endo- and myocarditis, as well as myositis, particularly involving red skeletal muscle. The aetiology of HSMI is currently unresolved, though a viral cause is suspected. Since its discovery in 1999, HSMI has become an increasing problem for the Norwegian farming industry, with some farms experiencing yearly outbreaks and subsequent economic losses. In the present study an Atlantic salmon farm was studied from December 2003 to April 2005. Samples from apparently healthy as well as clinically diseased fish were collected monthly and examined histopathologically. The first fish to be diagnosed with HSMI was sampled in May, 8 months after transfer to sea. A clinical outbreak of HSMI followed in June, when all fish in the sample had lesions consistent with HSMI. Subsequent samples revealed that cardiac lesions decreased in severity 2 months after the start of the outbreak, but that multiple foci of cellular infiltration and necrosis persisted throughout the year. There appeared to be a shift in lesion location from being most severe in the compact myocardium in early stages of disease to a greater involvement of the atrium and spongy layer of the ventricle in later samples. Late samples also showed increased fibrosis of cardiac tissue. In conclusion, HSMI appears to be a severe disease with elevated mortality, morbidity close to 100% and prolonged duration.     

Presence of multiple viruses in non-diseased, cultivated shrimp at harvest

Histological examinations were carried out with 400 cultivated black tiger shrimp (Penaeus monodon) from 12 commercial rearing ponds from three different areas in Thailand over a period of 3 years. The shrimp were collected at or near harvest time as two arbitrary size groups of 10–20 each from each pond. Aside from size difference, they showed no gross signs of disease and were normally active. Pathognomonic histopathological lesions were found only for hepatopancreatic parvovirus (HPV) or monodon baculovirus (MBV). Although these were relatively frequent, no unusual shrimp mortality had occurred in any of the ponds examined. Severity of these infections was negatively correlated with shrimp size. When grouped together, HPV-infected shrimp gave mean lengths of approximately 6.5 cm that were significantly different from uninfected shrimp at 9 cm length, early in the cultivation cycle while MBV-infected groups of approximately 9 cm length were not readily distinguishable until uninfected shrimp were 10 cm or more, later in cultivation. Thus, HPV infection was correlated with more severe stunting than MBV. In addition to histopathological examination, polymerase chain reaction (PCR) assays for HPV, white spot syndrome virus (WSSV) and infectious hypodermal and hematopoietic necrosis virus (IHHNV) were carried out on one large sample of 240 shrimp from 6 ponds where visible lesions were apparent for MBV only. Surprisingly, 94% of the specimens gave a positive test for at least one of the four viruses. HPV and IHHNV alone or in combination were detected at high prevalence (approximately 60%) despite the absence of visible histological lesions and were confirmed by southern blot hybridization. Although the prevalence of the four viral pathogens was very high, it would normally have gone unnoticed, since normal shrimp are rarely examined for viruses.     

Characterization of Mycobacterium salmoniphilum as causal agent of mycobacteriosis in Atlantic salmon,Salmo salar L., from a freshwater recirculation system

Thirty Atlantic salmon, Salmo salar L., with low corporal condition relative to other fish present in the culture system, were sampled from a freshwater recirculation pisciculture located in Chile. The most characteristic signs and lesions were cachexia and presence of multiple greyish‐white granulomas within internal organs. The external and internal lesions, along with the microscopic, histologic and biochemical findings, were consistent with mycobacteriosis. The identification of Mycobacterium salmoniphilum as the causal agent of the lesions was possible through the use of molecular analyses. This study represents the first report of Mycobacterium salmoniphilum in a freshwater recirculation system and the first case of fish mycobacteriosis described in Chile.     

Evaluation of immunological parameters in farmed gilthead sea bream, Sparus aurata L., before and during outbreaks of 'winter syndrome'

In recent years, 'winter syndrome' has caused severe economic losses in many marine farms in southern Europe. This study compared the activity of the immune system in healthy, asymptomatic and diseased gilthead sea bream. Serum protein and immunoglobulin content were evaluated as well as serum complement activity from these groups of fish. Differential leucocyte counts were also determined. Immunological assays were performed to determine intra- and extracellular 'respiratory burst' activity as non-specific immune response parameters. Diseased fish showed a significant reduction in haemolytic activity (90%), and in serum proteins and immunoglobulins in comparison with the other groups. A significant increase in the lymphocyte percentage (50%) and a decrease in the granulocyte percentage (over 70%) was found in asymptomatic fish. Respiratory burst activity was reduced in both the clinical and preclinical stages of the disease, compared with the controls. These observations confirm a severe immunodeficiency in diseased fish but also the presence of a cellular immune dysfunction in fish without clinical signs, before the onset of the disease.     

A study of gross,histological and blood biochemical changes in rainbow trout,Oncorhynchus mykiss (Walbaum), with rainbow trout gastroenteritis (RTGE)

The mechanisms behind the pathogenesis of rainbow trout gastroenteritis (RTGE) are still unknown. This study examined the macroscopic and microscopic changes in trout with RTGE (RTGE+), as well as the blood chemistry. A total of 464 rainbow trout were sampled from 11 sites in the UK, comprising 152 RTGE+ fish and 330 random, apparently healthy fish. A case definition for RTGE was assessed by the analysis of its agreement with three laboratory tests: histopathology, packed cell volume and kidney bacteriology. Cluster analysis indicated the presence of three distinct presentations within the population of RTGE+ fish. Cluster A included gross signs associated with moribund RTGE+ fish, and clusters B and C identified gross signs consistent with concurrent diseases, notably furunculosis, enteric redmouth and proliferative kidney disease. The information gained was used to select RTGE+ fish without concurrent disease for the analysis of RTGE pathogenesis with blood biochemistry. This analysis revealed a severe osmotic imbalance and a reduced albumin/globulin ratio as indicatives of selective loss of albumin. These findings are compatible with a protein losing enteropathy.     

Streptococcosis,Lactococcosis and Enterococcosis are potential threats facing cultured Nile tilapia (Oreochomis niloticus) production

Streptococcosis, lactococcosis and enterococcosis are among the most important bacterial diseases affecting tilapia farms in Kafr Elsheikh governorate, Egypt. A number of clinically diseased fish were collected and submitted to our laboratory during disease outbreak in 2018. They were characterized by nervous swimming behaviour, skin darkness, exophthalmia, ocular opacity and haemorrhages. Necropsy findings were splenomegaly, congestive hepatomegaly, liquefied brain and enteritis. The phenotypic and molecular characterizations of the bacterial strains isolated from naturally infected fish identified three genera of Gram‐positive cocci: Streptococcus agalactiae, Enterococcus faecalis and Lactococcus garvieae. Infectivity trials were conducted in four groups of Nile tilapia inoculated with S. agalactiae Egy‐1, E. faecalis Egy‐1 and L. garvieae Egy‐1 strains and saline. Mortalities, clinical signs and pathological findings were recorded daily 14 days post infection. Experimentally infected tilapia showed similar clinical signs, postmortem lesions, but varied in the severity and experienced high mortalities up to 70% in case of S. agalactiae and L. garvieae infections and 30% in case of E. faecalis infection. Pathological examination of infected tissue sections stained with modified Brown–Brenn and immunohistochemistry revealed an important direct correlation between the distribution of each bacterial isolate and the lesions developed in different organs. Furthermore, the isolates were subjected to profiling against 11 antibiotics, and they showed resistance against several types of antibiotics, which implicate potential risk to human health and emphasize the urgent need for alternate bio‐control strategies to prevent the diseases and the problem of multidrug resistance in aquatic environment.     

Edwardsiella tarda infection in Korean catfish,Silurus asotus,in a Korean fish farm

Mass mortality of Korean catfish, Silurus asotus, occurred in a culture farm situated in Jeollabukdo Province, Korea. The cumulative mortality rates reached up to 5% of the total fish in the farm per day. In clinical signs, the affected fish showed abdominal distension, vent protrusion, enteritis, liver congestion and abscess‐like lesions in enlarged spleen and kidney. Histopathologically, in the liver, hepatocytes lost fat and underwent atrophy or necrosis. The spleen showed necrotized splenocytes and a haemorrhagic pulp. In the kidney, glomerular destruction, degeneration of renal tubular epithelial cell and haemorrhage were observed. However, necrotic muscular lesions were not observed. A pure bacterial isolate was obtained from the liver, spleen and kidney lesions of affected fish. Experimental infection of normal catfish with the isolate resulted in the development of clinical signs similar to those seen on the farm. The isolates were identified as Edwardsiella tarda through biochemical tests (99.4%) and analysis of bacterial genes (16S rDNA) sequences (98%). The bacteria possessed two virulent genes: sodB and katB genes. These results suggest that E. tarda can act as a pathogen of farmed catfish. This is the first report showing that E. tarda caused mortality in cultured Korean catfish.     

Acid water and aluminium exposure: experimentally induced gill lesions in brown trout, Salmo trutta L.

Abstract. Brown trout gills were examined after exposure to different aluminium concentrations (50, 200,500μg/1) at pH 5.5 and 7.0 for up to 6 weeks. The influence of humus (Pt 0, Pt 20) and water temperature (2.5°C, 15°C) was recorded. The gill structure was studied by light, scanning and transmission microscopy, together with a complementary morphometric analysis of centrally located secondary lamellae. Low water temperature (2.5°C) resulted in advanced gill lesions after exposure to aluminium at pH 5.5. The lesions were characterized by enlargement of the secondary lamellae due to an increased number of chloride cells in the epithelia. Furthermore, the chloride cells contained cytoplasmic aluminium precipitates. Addition of humus (Pt20) or increased pH (7.0) reduced or inhibited the effects of aluminium on the gills. A high water temperature (15°C) reduced the early gill lesions observed after exposure to water at 2.5°C. Prolonged exposure to a temperature of 15°C resulted in alterations in the gill structure in all groups, including the control group.     

Infection of Tilapia Oreochromis sp. by Vibrio vulnificus in Freshwater and Low-salinity Environments

The first isolation of Vibrio vulnificus in southern Taiwan from hybrid tilapia Oreochromis sp. raised in freshwater and brackish water environments is documented in this report. The infection was only found in fish in ponds where the salinity was less than 10 ppt. Tilapia raised in water of higher salinities in the same region were not affected. Grossly visible signs of infection included dark coloration, lethargy, and external hemorrhage and ulceration of the skin. The most prominent internal signs of infection included splenomegaly and severe hemorrhagic lesions in the liver. Septicemia was documented in moribund fish. All bacterial isolates from moribund fish were tested by polymerase chain reaction, using V. vulnificus hemolysin/cytolysin gene‐specific primers. Sequence data from the 16S ribosomal RNA gene suggest that these isolates were V. vulnificus. The isolates were indole and mannitol positive, characteristics shared by human clinical isolates and isolates from freshwater European eel, Anguilla anguilla. The isolates from tilapia were unique in that they were negative for ornithine decarboxylase and citrate.     

Pan-steatitis in farmed northern bluefin tuna, Thunnus thynnus (L.), in the eastern Adriatic

Clinical, gross and histopathological investigations were carried out into large-scale mortalities on eastern Mediterranean bluefin tuna, Thunnus thynnus (L.), farms. Fish showed only nervous signs and darkened colour. At post-mortem the liver was bronze coloured and the pyloric area waxy in consistency. There was no evidence of any other gross pathology. Histopathology showed severe hepatic necrosis and lipidosis. Peri-pancreatic lipoid tissue was heavily infiltrated with an inflammatory round cell infiltrate. Fish on all three farms had been fed on a North African pilchard diet rather than traditional local or Baltic species. Once the diet was modified, losses ceased. A diagnosis of pan-steatitis as seen in other farmed fish species, as well as in terrestrial animals, on particular fish-based diets was made, although the actual factor within the diet which induced the inflammatory effect is not known.     

Suspected myocardial necrosis in farmed Atlantic salmon, Salmo salar L.: a field case

Arteriosclerosis of the coronary artery has been described as a 'fact of life' for Pacific and Atlantic salmonids due to the high prevalence in spawning fish. The lesions are believed to be the result of overstretching of the highly distensible bulbus arteriosus whereby the endothelium of the main coronary vessel becomes mechanically damaged and a smooth muscle proliferation ensues with resultant partial occlusion of the vessel. The physiological significance for the function of the heart has yet to be demonstrated, but experimental studies show that, for example, swimming performance is compromised in fish in which the coronary artery has been ligated. This paper describes a case of myocardial necrosis in harvest-size Atlantic salmon during and after transportation to the slaughterhouse. Mortality during this process reached 10% in some of the transports and affected fish showed characteristic signs of congestive cardiac failure. Histology revealed extensive myointimal proliferation in the coronary artery and patchy necrosis of the compact ventricular myocardium. Several unfavourable factors such as high water temperature, skeletal malformations and crowding all probably contributed to extra cardiac workload. To the best of our knowledge, this is the first reported field case showing a link between coronary lesions and severe cardiac pathology.     

Pyelocystitis in breeding sows

Pyelocystitis results from ascending infection of the urinary tract with Corynebacterium suis in sows. Infection occurs regularly during coitus by healthy boars, which are often contaminated with Corynebacterium suis. Characteristic clinical signs of pyelocystitis are haematuria, anemia and emaciation. The whole urinary tract shows severe purulent-necrotic inflammation with progressive vascular lesions. Diagnosis is based on clinical, pathological and bacteriological findings. Distinct changes in urine samples are present. Treatment is only successful in sows with intact function of kidneys. In early detected cases treatment can be effective with repeated application of appropriate antibiotics, e.g. penicillin or ampicillin. There are no proven methods of prevention.