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.     

Gastric dilation and air sacculitis in farmed chinook salmon, Oncorhynchus tshawytscha (Walbaum)

A syndrome affecting cultured chinook salmon, Oncorhynchus tshawytscha (Walbaum), characterized by distended abdomens, gastric dilation, air sacculitis (GDAS), increased feed conversion rates and increased mortality has been recognized in New Zealand. Affected fish were most obvious in sea cages but were also present in fresh water. Mortality rates associated with this condition were highest in late summer and approached 6% per month. A dilated and flaccid stomach, without visible rugal folds containing copious oil, watery fluid or undigested feed was typical. Gastric mucosal ulceration or inflammation were not present. The air sacculitis consisted of a thickened, dilated bladder with a mixed mucosal inflammatory infiltrate and a luminal exudate associated with large numbers of morphologically diverse bacteria. Gastric dilation or air sacculitis occurred alone or together in the same fish. In a group of 20 subclinically affected fish with or without gastric dilation, there were no significant differences in weight, length, serum osmolality, sodium, total protein or packed cell volume. Twenty-three severely affected fish had significantly ( P  < 0.05) higher serum osmolality but similar sodium and total protein to that of clinically normal fish.     

Field Efficacy of Florfenicol for Control of Mortality in Channel Catfish, Ictalurus punctatus (Rafinesque), Caused by Infection With Edwardsiella ictaluri

A field study to assess the efficacy of florfenicol (FFC) against enteric septicemia of catfish (ESC) was conducted with pond‐reared channel catfish fingerlings held in 0.1‐acre earthen ponds. Fish were challenged with Edwardsiella ictaluri in a natural pond outbreak or by cohabitation with E. ictaluri‐infected fish held in netpens. Fourteen ponds were assigned in equal number to two treatment groups, that is, either treated (with 10 mg FFC/kg body weight in medicated feed) or not treated (control) for 10 consecutive d. The threshold for enrollment into the study was 0.3% cumulative mortality attributed to ESC. Treatment was initiated on different dates for each pond because each pond was enrolled when 33 fish/pond were diagnosed with ESC based on clinical signs, lesions, or positive cultures. Mortality was monitored during the 10‐d treatment period and during a 14‐d posttreatment observation period. At the end of the 14‐d posttreatment observation period, all fish were euthanized, and 20 fish from each pond were examined by gross necropsy and evaluated for the presence of E. ictaluri by bacterial culture. The odds of a mortality in the control group were 2.20 times the odds of a mortality in the FFC‐treated group. Significantly fewer (P≤ 0.05) FFC‐medicated catfish died in comparison to unmedicated catfish. The minimum inhibitory concentration of FFC for this strain of E. ictaluri was 0.25 μg/mL in all fish that were assayed. The mean zone of inhibition (Kirby Bauer) was 36.8 mm from E. ictaluri isolates of test fish. There were no FFC treatment‐related lesions seen on gross pathology. FFC was efficacious and safe for control of mortality from E. ictaluri infection in catfish.     

Efficacy of Sarafloxacin Hydrochloride in Treating Naturally-Induced Edwardsiella ictaluri Infections in Channel Catfish,Ictalurus punctatus

Sarafin (sarafloxacin hydrochloride), a new antibacterial, was evaluated in the field on a naturally induced infection of Edwardsiella ictaluri in channel catfish, -Ictalurus punctatus. Healthy channel catfish (mean weight = 50 g) were stocked into nine cages at 200 fish per cage in a pond with an undergoing E. ictaluri infection. Seven days after stocking, dead fish were observed in the cages with clinical signs of enteric septicemia of channel catfish (ESC). After E. ictaluri was confirmed through isolative biochemical tests, medicated feed was applied for five consecutive days. During this period, fish in three control cages received a commercial 32% protein floating feed, three other cages of fish served as positive controls and were fed Romet, and three cages received the test feed with Sarafin. Both medicated feeds reduced the increase in cumulative percent mortality. In the control cages, cumulative percent mortalities continued to increase throughout the study period. Average daily mortality rates were significantly lower following both treatments of medicated feed, and treatments receiving Sarafin showed the greatest reduction in average daily mortality rates. Average daily mortality rates in the control did not change after the medicated feeding period. Toward the end of the study, temperatures reached 30°C, above the active range of ESC infections, and all mortalities ceased.     

Histopathology of experimental Streptococcus sp. infection in tilapia, Oroochromis niloticus (L.), and channel catfish, Ictafurus punctatus (Ratinesque)

Nile tilapia, Oreochromis niloticus (L.), and channel catfish, Ictalurus punctatus (Rafinesque), were experimentally infected by immersion with three isolates (Lake, DL8O5 and MS91452) of Streptococcus sp. from diseased fish. To enhance infection, the lateral body surface of each fish was scraped prior to bacterial exposure. The Lake and DL8O5 isolates caused exophthalmia, ocular opacity and ocular haemorrhage in some tilapia. Histopathology of these fish revealed; meningitis; polyserositis of heart, liver, spleen, ovary and kidney; splenitis; ovaritis; and myocarditis. Isolate MS91452 induced only mild granulomas in spleen, kidney and ovary of tilapia. The Lake and DL8O5 isolates induced endophthalitis, Channel catfish infected with the Lake and DL805 isolates developed similar eye lesions to tilapia. Histologic lesions caused by all three isolates in channel catfish consisted of meningoencephalitis, mild myocarditis, splenitis and ovaritis, but these lesions were not as severe as in Nile tilapia.     

Efficacy of a Live‐attenuated Edwardsiella ictaluri Oral Vaccine in Channel and Hybrid Catfish

This study evaluated the efficacy of an oral live‐attenuated Edwardsiella ictaluri vaccine against enteric septicemia of catfish (ESC) in channel and hybrid catfish. The vaccine was delivered one time orally by feeding fish a diet coated with an attenuated E. ictaluri isolate at four doses to deliver between 4 × 10⁶ to 3.2 × 10⁷ viable vaccine cells/g wet feed. Thirty‐five days postvaccination, control and vaccinated fish were challenged with virulent E. ictaluri and mortality was examined for 30 d postchallenge. Mortality of nonvaccinated hybrids (85%) and nonvaccinated channel catfish (73%) was similar but significantly greater than all groups of vaccinated fish. In channel catfish, a trend toward increasing mortality with decreasing dose was observed. Mortality of channel catfish vaccinated with the lowest dose (26.6%) was significantly higher than fish vaccinated with the highest dose (14.1%) but similar to fish vaccinated at the intermediate doses (17.5 and 19.4%). In contrast, mortality of four doses of vaccinated hybrid catfish was similar and ranged between 10.4 and 14.0%. The data demonstrate that the attenuated E. ictaluri vaccine at all four doses tested is effective at reducing ESC‐related mortalities in hybrid and channel catfish.     

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.     

Mortality and pathology of hybrid catfish,Clarias macrocephalus (Günther) × Clarias gariepinus (Burchell), associated with Edwardsiella ictaluri infection in southern Thailand

Enteric septicaemia of catfish (ESC) caused by Edwardsiella ictaluri is becoming an increasing problem in aquaculture and has been reported worldwide in a variety of fish species. This study reports ESC in hybrid catfish, Clarias macrocephalus (Günther) × Clarias gariepinus (Burchell), cultured in southern Thailand. The bacteria were identified as E. ictaluri by conventional and rapid identification systems, as well as by genetic and phylogenetic characterization. Analysis of 16S rRNA indicated 100% homology to the 16S rRNA sequence of several E. ictaluri strains in GenBank. Plasmid profiles demonstrated 4.0‐ and 5.6‐kb plasmids, compared with the 4.8‐ and 5.6‐kb plasmids in the US isolates, and representative genes of three of the four known pathogenicity islands of US isolates were present. Serologically, lipopolysaccharide (LPS) purified from the Thai isolates was not recognized by a monoclonal antibody against the LPS of US isolates. Fish experimentally infected with E. ictaluri showed 23–100% mortality within 14 days with a 168‐h LD₅₀ of 6.92 × 10⁷ CFU mL^?1 by immersion and a 96‐h LD₅₀ of 1.58 × 10⁶ CFU fish^?1 by intraperitoneal injection. Examination of tissue sections obtained from both naturally and experimentally infected fish indicated that infection of hybrid catfish with E. ictaluri produced lesions in several organs including liver, kidney, spleen, heart and brain. Histopathology findings included cellular necrosis, focal haemorrhage, infiltration of lymphocytes and multifocal granulomatous inflammation in the infected organs.     

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.     

Application of Compensatory Growth to Enhance Production in Channel Catfish Ictalurus punctatus

Four treatment groups that received repeating cycles of fixed feed deprivation for either 0, 1, 2, or 3 d (control, treatment 1, treatment 2, and treatment 3, respectively), followed by periods of refeeding with a 36% protein commercial catfish feed once daily as long as the active phase of compensatory growth (CG) persisted, were assessed in flow-through aquaria. No-feed periods elicited the CG state and were immediately followed by days of ad libatum refeeding. At the end of 10 wk, average growth rate (AGR) of fish was higher ( P < 0.05) than the control by 40%, 180%, and 191% for treatment 1, treatment 2, and treatment 3, respectively. The average weight of fish in treatment 3 was heavier ( P < 0.05) than the average control group at the end of the study period. Mean daily feed consumption was 3.91%, 5.03%, 5.36%, and 5.98% for control, treatment 1, treatment 2, and treatment 3, respectively. Mean feed consumption per fish per day was 24%, 71.3%, and 70.7% higher than the control in treatment 1, treatment 2, and treatment 3, respectively. Restricted feeding is one of the effective methods to contain ESC-related losses in commercial channel catfish fingerling operations. The mean cumulative survival of treatment groups registered higher ( P < 0.05) survival to Edwardsiella ictaluri infection compared to the daily fed control fish. Results from this study show that compensatory growth response triggered by periodic non-feeding days can improve growth rate, feed consumption, and improved survival to ESC infections in channel catfish fingerlings.     

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.     

Economic assessment of commercial-scale Edwardsiella ictaluri vaccine trials in U.S. catfish industry

Abstract

Enteric Septicemia of Catfish (ESC) is a ruinous bacterial disease affecting the U.S. catfish industry. Previous attempts to develop ESC vaccines have failed to achieve industry acceptance, largely attributed to difficulties in delivering the vaccine to immunocompetent fish. Recently, a live attenuated ESC vaccine has been developed, coupled with a mechanized platform designed to accurately deliver measured doses of vaccine with feed. This delivery scheme for vaccine-feed admixture has shown tremendous promise under controlled research settings. This study evaluated the economic effects of on-going commercial-vaccination trials on catfish fingerling operations in Mississippi. Commercial-vaccination trials for both channel and hybrid catfish demonstrated significant improvement in survival, growth, feed consumption, feed conversion and gross yield. At a realistic vaccination cost of $750/ha, the net economic benefits to channel and hybrid catfish fingerling-production phases were $3199 and $6145/ha, respectively. Whole-farm models showed additional profit ranging from $71,758 to $133,887/400-ha on farms that integrate fingerling production to their production strategies due to appropriation of more of the otherwise incumbent fingerling production acreage into foodfish production. Commercial adoption of the oral-vaccination platform would greatly enhance profitability while laying the foundation for development and delivery of polyvalent vaccines against other catfish diseases.     

Outbreaks of ulcerative disease associated with ranavirus infection in barcoo grunter,Scortum barcoo (McCulloch & Waite)

In 2013, an outbreak of ulcerative disease associated with ranavirus infection occurred in barcoo grunter, Scortum barcoo (McCulloch & Waite), farms in Thailand. Affected fish exhibited extensive haemorrhage and ulceration on skin and muscle. Microscopically, the widespread haemorrhagic ulceration and necrosis were noted in gill, spleen and kidney with the presence of intracytoplasmic eosinophilic inclusion bodies. When healthy barcoo grunter were experimentally challenged via intraperitoneal and oral modes with homogenized tissue of naturally infected fish, gross and microscopic lesions occurred with a cumulative mortality of 70–90%. Both naturally and experimentally infected fish yielded positive results to the ranavirus‐specific PCR. The full‐length nucleotide sequences of major capsid protein gene of ranaviral isolates were similar to largemouth bass virus (LMBV) and identical to largemouth bass ulcerative syndrome virus (LBUSV), previously reported in farmed largemouth bass (Micropterus salmoides L.), which also produced lethal ulcerative skin lesions. To the best of our knowledge, this is the first report of a LMBV‐like infection associated with skin lesions in barcoo grunter, adding to the known examples of ranavirus infection associated with skin ulceration in fish.     

Nifurpirinol (Furanace; P-7138) related lesions on channel catfish Ictalurus punctatus (Rafinesque)

Abstract. Skin lesions developed on channel catfish, Ictalurus punctatus , exposed to 0-5 mg/1 Furanace for 4 or 14 days. Lesions developed 3 days after the 4-day exposure and on the eleventh day of the 14-day exposure. The lesions continued to develop after the fish were moved to untreated water. The lesions which began as dull areas of skin, sometimes resulted in erosion of skin and muscle which exposed the vertebrae. Bacteria were not isolated from the lesions except those with severely eroded muscle. The gills possessed lesions characteristic of a response to a toxic chemical agent.     

Validation of a qPCR assay for the detection of Ictalurid herpesvirus‐2 (IcHV‐2) in fish tissues and cell culture supernatants

Ictalurid herpesvirus‐2 (IcHV‐2) is a pathogen of cultured black bullhead, Ameiurus melas (Rafinesque), and has been shown to produce high mortality in experimental exposures of channel catfish, Ictalurus punctatus (Rafinesque). During acute infections, the virus grows readily in cell cultures but produces a cytopathic effect (CPE) similar to that of Ictalurid herpesvirus‐1 (IcHV‐1) and the channel catfish reovirus. We have developed a quantitative PCR assay that can be used to detect IcHV‐2 in fish tissues and cell culture supernatants. The assay does not amplify other fish herpesviruses tested or host DNA. It is quantitative over a range of eight logs, and the limit of detection is <10 copies per reaction. In replicate assays carried out on different days, the coefficient of variability was 10%. The best organs for the detection of acute IcHV‐2 infections by our assay are the spleen and kidney. This assay should be useful for the diagnosis of IcHV‐2 disease, the identification of syncytial CPEs in cell cultures, and for the detection of latent infections in carrier fish.     

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.     

Epizootics in farm-raised channel catfish, Ictalurus punctatus (Rafinesque), caused by the enteric redmouth bacterium Yersinia ruckeri

In the winters of 1995 and 1996, unusual disease outbreaks occurred on two separate channel catfish farms in Arkansas, USA. Affected fish exhibited extraordinary haemorrhaged rings around the eyes and raised haemorrhaged areas overlying the frontal foramens. Other signs included abnormal swimming, lethargy, loss of equilibrium, and exophthalmia. Bacterial isolates from the moribund fish were identified as Yersinia ruckeri by biochemical tests, no lysis by the Hafnia-specific bacteriophage 1672, and Y. ruckeri-specific growth patterns on Shotts-Waltman media. Fingerling catfish injected intraperitoneally with the bacterial isolate at 7.8 × 10⁶ bacteria fish^?1 developed lesions characteristic of the epizootics at 13, 18, and 22 °C and a biochemically identical isolate was recovered. Fingerling rainbow trout injected with the channel catfish isolate at 1 × 10⁵ bacteria fish^?1 and held at 20 °C developed signs typical of enteric redmouth by 4 days post-inoculation and were moribund by 5 days post-inoculation. Some differences of clinical signs occurred between experimentally infected rainbow trout and channel catfish. Clinical and biochemical similarities between infections of Y. ruckeri and many warmwater pathogens in affected catfish may lead to incorrect diagnosis of ERM infections.     

Impact of Double-Crested Cormorant Depredations on Channel Catfish Farms

Resurgent wintering populations of double-crested cormorants in the past 10 years have caused serious depredation problems for commercial channel catfish ( Ictalurus punctarus ) growers in Mississippi. Catch rates of catfish by cormorants were found to average 5 catfish per cormorant-hour. Catfish taken averaged 12 cm in length. However, cormorants took fingerling catfish at rates as high as 28 per cormorant-hour. The average number of cormorants found feeding on a single pond in this study was 30.5. If this number (but not necessarily the same individuals) fed all day in an 8 ha pond stocked at 51,000 fishlha, the fish population would be halved in 30 days. Further, using this example, the cost of harassment patrols on a 200 ha catfish farm complex over a 5 month period would be exceeded in 22 days by the losses in this one pond. Wild gizzard shad ( Dorosoma cepedianum ) occurred in some ponds, and seem to be preferred by cormorants over caffish.     

Comparison of the lipid properties of healthy and pansteatitis‐affected African sharptooth catfish,Clarias gariepinus (Burchell), and the role of diet in pansteatitis outbreaks in the Olifants River in the Kruger National Park,South Africa

Pansteatitis has been identified in wild populations of sharptooth catfish, Clarias gariepinus (Burchell), and Nile crocodiles, Crocodylus niloticus Laurenti, inhabiting the same waters in the Olifants River Gorge in the Kruger National Park, South Africa. Mesenteric and pectoral fat tissue was investigated microscopically and by fatty acid analysis in healthy and pansteatitis‐affected catfish from both captive and wild populations. Variation in fatty acid composition between pectoral and mesenteric fat was noted. Composition of mesenteric fat differed between fish from various localities as a result of differences in diet. Pansteatitis in the captive population, resulting from ingestion of high amounts of dietary oxidized fat, reflected higher levels of unsaturated fatty acids within the mesenteric fat. Mesenteric fat of pansteatitis‐affected wild catfish was characterized by an increase in moisture content, a decrease in fat content and a decrease in stearic and linoleic acids. The n‐3 to n‐6 fatty acid ratio of mesenteric fat was higher in pansteatitis‐affected wild catfish than in healthy catfish from the same locality, reflecting higher polyunsaturated fat intake by pansteatitis‐affected fish. The possible role of alien, invasive, phytoplankton‐feeding silver carp, Hypophthalmichthys molitrix (Valenciennes), in the aetiology of pansteatitis in both catfish and crocodiles in the Olifants Gorge is discussed.