Unilateral exophthalmos in Sebastes spp.: histopathologic lesions

Abstract. A spontaneous unilateral exophthalmos occurring in five species of otherwise healthy rockfish, Sebastes spp., was investigated. All eyes from nine unilaterally exophthalmic and seven non-exophthalmic rockfish were examined grossly and histologically. In all affected fish the exophthalmos was due to enlargement of the globes resulting from the formation of choroidal cysts filled with a clear, watery fluid and surrounded by dense, aberrant connective tissue. Cyst formation led to gross distortion and disorganization of the choroid. Distorted remnants of the choroidal rete mirabile contained markedly fewer erythrocytes, a homogeneous proteinaceous material and a mild inflammatory cell infiltrate. Thickened scleral cartilage with disoriented chondrocytes was also present in exophthalmic eyes. Some of the affected eyes showed pigmentary abnormalities with clumps of heavily pigmented cells present in the retina and choroid. Retinal degeneration and detachment was also evident in some of the affected eyes.     

Haemoglobin and oxygen transport of the West Australian dhufish, Glaucosoma hebraicum Richardson, and other species

To better understand the possible role of deoxygenation of haemoglobin in the pathogenesis of exophthalmos in the West Australian dhufish, Glaucosoma hebraicum Richardson, some oxygen transport properties of haemoglobin from this species were determined and compared with haemoglobin from black bream, Acanthopagrus butcheri (Munro), snapper, Pagrus auratus (Bloch & Schneider) and King George whiting, Sillaginodes punctata (Cuvier). Dhufish had a single haemoglobin with a pronounced Root effect. Snapper and black bream blood had six and five types of haemoglobin, respectively. The magnitude of the Root effect of haemoglobins in the haemolysate was demonstrated by comparing oxygenation and total deoxygenation at pH 8 with relative deoxygenation at pH 6.9. Dhufish haemoglobin demonstrated a large Root effect, with the Root effect of King George whiting, snapper and black bream being of lesser magnitude. Deoxygenation of all haemolysates was more pronounced in the presence of adenosine triphosphate (ATP). Seasonal changes in haematological parameters and ATP content of dhufish blood were not evident. The Root effect is discussed in the context of its possible role in oxygen supply to the retina and adaptation to the fish's habitat and the environment.     

The experimental histopathology of Lernaea polymorpha Yu, 1938 infection in naive Aristichthys nobilis (Richardson) and a comparison with the lesion in naturally infected clinically resistant fish

Abstract. Bighead carp, Aristichthys nobilis (Richardson), fingerlings which had not been previously exposed to nauplii of Lernaea polymorpha were infected and sacrificed at various time intervals up to 21 days. Clinical observations showed that punctate haemorrhages developed following skin penetration at 13 days post-exposure. The adult female parasite was observed embedded in the skin and histopathology showed that the parasite penetrated the host tissue at an angle, sliding between the overlapping scales. It caused extensive tissue disruption, necrosis and haemorrhage along its path of entry, which was followed by an acute inflammatory response succeeded by a highly vascular chronic granulomatous fibrosis, whereby collagen fibres encapsulated the horns of the parasite. This contrasted with the predominantly haemorrhagic ulcerative lesions examined on immune fish subjected to natural infection, which were extensive but rarely accompanied by penetration through the dermis. There was a very extensive infiltrate of eosinophilic granular cells, club cells and lymphocytes within the spongiotic epidermis and the extensive haemorrhage was largely subepidermal.     

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.     

Detection of Cyprinid herpesvirus 2 in association with an Aeromonas sobria infection of Carassius carassius (L.), in Italy

Sixteen specimens of female crucian carp, Carassius carassius (L.), during the breeding season, were investigated for post‐mortem and full diagnostic examination during a mortality outbreak in a tributary stream of the Arno River in Tuscany in 2011. Necropsy highlighted the presence of a swollen anus and widespread haemorrhages in the body, fins, gills and eyes. Haemorrhages in internal organs and spleen granulomas were also observed. Bacteria isolated from the brain, kidney and spleen of affected fish were identified as A. sobria. Microscopic lesions observed in gills were characterized by necrosis of the secondary lamellae, congestion and multifocal lamellar fusion. The kidney showed necrosis, oedema, fibrin exudation and areas of haemorrhages, while in the spleen the main lesions were by multifocal necrosis of the lymphoid tissue. In the gills, transmission electron microscopy revealed herpesvirus‐like particles, subsequently identified as Cyprinid herpesvirus‐2 (CyHV‐2) with a nested PCR protocol. Although it was not possible to attribute a pathogenic role to CyHV‐2 in this mortality event, the identification of this herpesvirus in crucian carp increases the concern about its potential role in this species.     

Retinal and lenticular lesions in vitamin-C-deficient juvenile red drum, Sciaenops ocellatus (L.)

Abstract Ocular pathologic findings in eyes of ascorbic acid-deficient juvenile red drum, Sciaenops ocellatus (L.), are described. Abnormalities in the most severely affected eyes included: reduced globe size and lack of normal globe rigidity; vascular congestion and intraocular haemorrhage; lenticular lesions which included disorganization of posterior cortex, vacuolation of posterior subcapsular cortex and posterior migration of lens epithelium; and severe central retinal degeneration. The authors suspect that retinal degeneration was related to phototoxic injury, to which these fish had increased susceptibility as a result of ascorbic acid deficiency. The cause for lenticular lesions was undetermined, but may have been related directly to ascorbic acid deficiency, indirectly to retinal degeneration, or both.     

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.     

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.     

Pathology of experimental enteric septicaemia in channel catfish, Ictalurus punctatus (Rafinesque), following immersion-exposure to Edwardsiella ictaluri

Abstract. Fingerling channel catfish, Ictalurus punctatus (Rafinesque), were exposed experimentally to Edwardsiella ictaluri by immersion for 1 h in water containing 5 × 10⁸ colony-forming units (CFU) of the bacterium per ml. Ninety per cent of the fish developed lesions typical of enteric septicaemia of catfish (ESC), 93% of affected fish developed the acute form of ESC and 7% developed chronic ESC. Acute disease was characterized grossly by cutaneous haemorrhage and ulceration, and microscopically by enteritis, olfactory sacculitis, hepatitis and dermatitis. The earliest lesions of acute ESC, i.e. enteritis and olfactory sacculitis, were observed microscopically at 2 days post-exposure (PE); gross lesions, primarily mild subcutaneous haemorrhage at the base of fins, were first apparent at 4 days PE. Chronic ESC, seen most commonly 3–4 weeks PE, was characterized by dorsocranial swelling and ulceration, granulomatous olfactory neuritis/perineuritis, and meningoencephalitis involving the olfactory bulbs, olfactory tracts and olfactory lobes of the brain. Gross and microscopic lesions in the acute and chronic forms of experimental ESC were similar to the lesions reported in naturally occurring ESC. Definitive pathogenesis of acute and chronic ESC remains to be determined.     

Environmental parameters controlling growth of Ostrea edulis L. and Pecten maximus L. in suspended culture

Oysters (Ostrea edulis) and scallops (Pecten maximus) were grown in lantern nets at three stations in Birterbuy Bay, Co. Galway, Ireland. Shell and tissue growth and mortalities were recorded over a period of 18 months. Sea water temperatures, salinities, particulate organic carbon concentrations (POC), particulate organic nitrogen (PON) concentrations, particle concentrations and volumes of the seston and current speeds were recorded during a growing season. Differences in growth between stations are explained in terms of differences in temperature, organic carbon content of the seston and current speeds.     

Haemorrhagic kidney syndrome of Atlantic salmon, Salmo salar L.

This report describes a new syndrome affecting farmed Atlantic salmon on the Canadian east coast that has resulted in increased morbidity and mortality in affected stocks. The major pathological findings are apparent only microscopically and include renal interstitial haemorrhage and acute tubular necrosis and tubular casting. As a result, the disease has become known as haemorrhagic kidney syndrome (HKS). Affected fish are lethargic and anorectic, and lack external lesions. Clinically, HKS fish are anaemic, hypoproteinaemic and hyperosmolalic, with increased serum concentrations of sodium and chloride. At necropsy, internal changes ranged from apparently normal to include one or several of the following: swelling and/or patchy reddening of the kidney, pale gills, exophthalmos, serosanguinous ascites, darkening of the posterior intestine and splenomegaly. Ultrastructurally, viral inclusions were found in the cytoplasm of erythrocytes of HKS fish, and there were unusual electron‐dense inclusions within the tips of renal tubular microvilli of HKS fish. The significance and relevance of the ultrastructural findings to HKS are unknown. Virus isolation was attempted using CHSE, RTG‐2, FH‐10, BB and EPC cell lines; no virus was isolated. Bacteriological analysis failed to reveal significant pathogens. Analysis of tissues for heavy metals and pesticides was negative. Assays for clostridial toxins, lipopolysaccharide and verotoxins were negative. The aetiology of HKS remains unresolved.     

Histopathology of red-sore disease (Aeromonas hydrophila) in naturally and experimentally infected largemouth bass Micropterus salmoides (Lacepede)

Abstract. The histopathology of red-sore disease, caused by the gram-negative bacterium, Aeromonas hydrophila , is described for largemouth bass, Micropterus salmoides . Externally, lesions range from those affecting a few scales (pin-point), to those associated with extensive chronic ulcerations; there is focal haemorrhage, oedema and dermal necrosis which exposes underlying muscles producing infiltration of mononuclear and granulocytic inflammatory cells. Internally, the liver and kidneys are foci for toxic products produced by A. hydrophila with, in the most severe cases, complete destruction of the structural integrity of both organs. Pathological changes were not serious in either the spleen or heart, even in cases with massive damage in the liver and kidney. Internal and external lesions were similar in both natural and experimentally induced infections. The pathobiology of red-sore disease in bass is postulated to be linked to elevated water temperature stimulating increased metabolism, decreased body condition and stress, leading to the increased production of corticosteroids and the concomitant rise in susceptibility to infection.     

Pathology of gas bubble disease in two air-breathing catfishes (Clarias batrachus Linn. and Heteropneustes fossilis Bloch.)

Gross pathology in Clarias batrachus and Heteropneustes fossilis, and histopathology in the liver, intestine and kidney and abnormalities in erythrocyte count/mm³ and haemoglobin g% of C. batrachus afflicted with gas bubble disease were studied over 96 h. Histopathology and blood abnormalities in H. fossilis could not be observed due to heavy mortality. A tilt in the swimming posture and an upward bend in the tail region were the first signs of the disease. Exophthalmia was noted and blebs containing gas bubbles appeared on the fins and other parts of the body. The blebs burst producing open lesions after 72 h, and the fins became necrotic.Histopathologic changes included, in the liver, vacuolation of cells, necrosis and cordal disarray; in the intestine, lesions in the villi, degeneration of the submucosa, cellular exudate production in the lumen and air bubbles in the villi; and in the kidney, degeneration of tubules and glomeruli and necrosis of haemopoietic tissue. Erythrocyte count and haemoglobin content showed a consistent and significant fall from 12.87 × 10⁶ to 6.91 × 10⁶/mm³ and from 9.33 to 7.00 g%, respectively, up to 72 h. Empty blood vessels were noted in the liver, intestine and kidney. Fish of both species regained normal swimming orientation, and erythrocyte count and haemoglobin content also showed recovery from the disease.     

The effect of water pH on swimming performance in rainbow trout (Salmo gairdneri,Richardson)

A Brett-type respirometer was used to measure the effect of water pH on swimming performance of rainbow trout (Salmo gairdneri). Variations in water pH between 6 and 9 had no measurable effect on maximum aerobic swimming speed. At water pH 4, 5, and 10, however, the critical velocity was only 55, 67, and 61% respectively of that recorded for fish in water of pH 7. Exposure to acid conditions increased coughing and breathing frequency. Acid exposure resulted in a decrease whereas alkaline exposure resulted in an increase in both whole blood and red blood cell pH. Blood gas and acid-base characteristics showed little change during swimming at 2.0 BL/second, but exhaustive swimming resulted in a marked and immediate drop in blood pH in fish in acid, alkaline and neutral water. The blood acid-base status was restored to resting levels after exercise in neutral and alkaline water, but the acidosis was maintained following exercise in acid water. Fatigue occurred earlier and blood lactate levels increased to a higher level in fish swum to exhaustion in acid or alkaline water, compared with fish in neutral water.     

Edwardsiellosis in farmed rainbow trout (Oncorhynchus mykiss)

Edwardsiella tarda was isolated from naturally infected rainbow trout (Oncorhynchus mykiss) in raceway culture on a commercial fish farm where the fish were kept at a density of 110 kg m^?3 and at a water temperature of 14°C and with a photoperiod of 13 h light:11 h dark. The clinical signs of diseased fish (150 ± 20 mm standard length) were anorexia and lethargy. The most striking lesions in the fish were in the liver. There were hyperaemia and haemorrhages; on histopathological examination, the liver displayed inflammatory infiltrate in portal area, focal necrosis, dilatation of blood sinus and activation of sinusoidal cells. Infection experiments, performed 2 years after isolation of the original culture of E. tarda, were carried out under laboratory conditions at water temperatures of 15, 18 or 24°C. All experimental fish (common carp, Prussian carp, tench), intraperitoneally injected with 8 × 10⁶ cells, demonstrated a total resistance to E. tarda.     

Anaesthetic effect of eugenol at different concentrations and temperatures on black tiger shrimp (Penaeus monodon)

The anaesthetic effects of eugenol on Penaeus monodon were investigated at the different eugenol concentrations (60, 110, 160 and 210 mg/L), water temperature (21, 26 and 31°C), air exposure time (3, 6, 9 and 12 min) and body weight (2.62 ± 0.27, 6.34 ± 0.36 and 11.43 ± 0.33 g). The anaesthesia and recovery time were recorded. The results showed that the anaesthesia time of the shrimp decreased with the increase in the eugenol concentration and water temperature, and the recovery time increased with the increase of the eugenol concentration and the decrease of water temperature. Under the same eugenol concentrations, the recovery time increased with the increase of air exposure time and body weight. Under the eugenol concentration range of 60–210 mg/L, the recovered rate was 100%. The results indicated that eugenol is a safe and efficient anaesthetic for P. monodon.     

Experimental infection of Atlantic salmon, Salmo salar L., with infectious salmon anaemia virus: a histopathological study

Recent reports of the isolation of infectious salmon anaemia virus (ISAV) from Atlantic salmon, Salmo salar L., affected by haemorrhagic kidney syndrome (HKS) suggest that ISAV can cause severe renal haemorrhage and necrosis in addition to well-known pathognomonic hepatocellular necrosis and haemorrhage. The prevalence of ISAV-induced pathognomonic renal HKS lesions and their correlation to pathognomonic hepatic lesions of infectious salmon anaemia (ISA) is not known. The present experimental infection of Atlantic salmon with a Canadian isolate of ISAV found that pathognomonic hepatic ISA lesions were present in 90.6% and pathognomonic renal HKS lesions in 78.1% of fish which died after the experimental challenge. Both pathognomonic hepatic ISA lesions and pathognomonic renal HKS lesions were found together in 65.6% of fish which died after ISAV challenge. The present study clearly demonstrates that ISAV can cause a very high prevalence of both HKS and ISA pathognomonic lesions.     

Fish mortality due to acute ammonia exposure

Abstract. Fish mortality in the River Umia, near Villagarcia de Arosa, Pontevedra, Spain, which occurred after a discharge from a food sewage works, is studied. Physico-chemical parameters of water samples from sewage and from the River Umia were studied and concentrations of ammonia sufficiently high to cause toxic effects in fish (702 mg/1 and 302 mg/1 as total ammonia) were found. The toxicity of two concentrations of ammonia was investigated on goldfish, Carassius auratus (L.), using water quality values the same as found in the River Umia, to obtain the same concentrations of un-ionized ammonia (2·13 mg/1 and 0·91 mg/1). Fish exposed to high concentrations died within 24 h and three of six, which were exposed to the lowest concentration died within 96h. All fish at first showed symptoms of hyper excitability and hyperventilation, and at times of rest showed a decrease in respiration. Post-mortem findings generally included gill congestion and haemorrhage.