Bacterial Kidney Disease has been reported wherever susceptible salmonid populations are present. There has been a dispute about the status of the diseases among different salmonid species and their susceptibility to the infection over the past years. In this regard, a considerable number of indicated the susceptibility of brook trout to BKD infection. In order to determine the status of bacterial kidney disease (BKD) in hatchery and wild populations of brook trout (Salvelinus fontinalis) in Michigan, (Renibacterium salmoninarum) R. salmoninarum prevalence and intensity were determined in representative samples from adult hatchery raised and wild stocks as well as their offspring from 2001 through 2005. The hatchery raised adult Iron River brook trout presented higher BKD prevalence than the brook trout caught from Cherry Creek. Generally, the BKD prevalence and intensity in hatchery and wild brook trout strains gradually decreased throughout the period from 2001 to 2004. The critical role played by hatchery practices to control the spread and minimize the prevalence of BKD among Michigan brook trout populations was discussed. Although most of the previous studies reported unimportant role of the male in transmission of R. salmoninarum, yet our results clearly demonstrated that males shed more R. salmoninarum along with their gametes than females. [Nature and Science. 2007;5(1):8-17].

For the past six decades, parasitic sea lampreys (Petromyzon marinus) have caused devastating losses to salmonid fisheries in the Great Lakes. To reduce the number of sea lampreys, the Great Lakes Fishery Commission began a large-scale program based on trapping male sea lampreys, sterilizing them, and releasing sterile males back into streams to compete with fertile males for spawning females. The transfer of lampreys among lakes can potentially lead to the transfer of various pathogens, and this has raised major concerns regarding the possibility of resident fish populations becoming infected by introduced pathogens. During a health inspection of sea lampreys collected from Lake Ontario, lampreys with obvious furuncle-like lesions (1–2 cm in diameter) were noticed. Most of the furuncles occupied the dorso-lateral musculature, and Aeromonas salmonicida subsp. salmonicida was isolated from the kidneys. This bacterium was cultured from kidneys of 2.5% of the sea lampreys collected from two locations within the Lake Ontario watershed in 2004. The identity of bacterial colonies was presumptively verified with biochemical reactions and confirmed with polymerase chain reaction. This is the first report of A. salmonicida infection in sea lamprey in the Great Lakes basin associated with furunculosis.

Reaching with the fertilized gametes to the production stage is a critical process for the success of aquaculture and restoration of wild fish programs worldwide. Iodophors are routinely used to disinfect both broodstocks and fertilized eggs to control vertical as well as horizontal transmission of fish pathogens. During three successive spawning cycles, the specific fish pathogens Aeromonas salmonicida and Renibacterium salmoninarum associated with typical clinical picture have been isolated from examined salmon before gamete collection. The prevalence approximately reached 51% and 79% for A. salmonicida and R. salmoninarum respectively. On the other hand, the R. salmoninarum was isolated from the collected eggs of the broadstocks used for spawning in the above mentioned cycles. Average prevalence of infection in tested eggs was 15%. At the pre-rinsing cycles, the bacterial load was determined as 1.2 × 10 and 0.6 × 10 CFU/plate for A. salmonicida and R. salmoninarum in spawners respectively. On the level of fertilized eggs, the load was determined as 0.2 × 103 CFU/plate and 0.1 × 103 for A. salmonicida and R. salmoninarum respectively. In the following spawning cycle, the efficacy of povidone iodine as surface disinfectant for returning spawners and fertilized eggs of Chinook salmon were tested. Concentrations of 60 mg/L povidone iodine for 30 minutes as initial dose followed by a maintenance dose of 70 mg/L for 10 minutes were applied as rinsing solutions for ♂ and ♀ Chinook salmon spawners. Eggs were shell-hardened in 80 mg /L povidone iodine for 30 minutes. Isolation trials from equal number of post rinsing spawner Chinook salmon and fertilized eggs indicated a sharp decline in bacterial colonies number per plate for spawners and eggs. The achieved post-rinsing results are highly indicative for the efficacy of povidone iodine as efficient disinfectant for both fish and eggs. Ultimately, the current study will ensure the production of fish populations with less bacterial load and consequent potent health status. [Life Science Journal. 2007; 4(3): 87 – 93 ] (ISSN: 1097 – 8135).

Diseases caused by Flavobacterium psychrophilum, a Gram-negative, long rod (0.2–0.75 · 1.5–7.5 lm) have recently become one of the most crucial problems affecting salmonid culture worldwide (Wood & Yasutake 1956; Pacha 1968; Lorenzen & Olesen 1997). In North America, the disease is known as cold water disease (CWD) because of its occurrence usually at low water temperature among different species of salmonids. The disease is characterized by skin erosions and ulcerations, darkening, fin and gill rot. In severe cases, the caudal fin is completely sloughed with the bare spine in the caudal peduncle area being completely exposed. In very young fish, the disease can also be associated with nervous manifestations such as erratic swimming behaviour and spiral movements (Holt, Amand, Rohovec & Fryer 1989; Kent, Groff, Morrison, Yasutake & Holt 1989). Flavobacterium psychrophilum has been reported in almost all salmonid species (Cipriano & Holt 2005). The bacterium has also been reported from other non-salmonid species including ayu, Plecoglossus altivelis (Temminck & Schlegel) (Lee & Heo 1998); common carp, Cyprinus carpio L.; crucian carp, Carassius carassius (L.); eel, Anguilla anguilla (L.) (Lehmann, Mock, Stuerenberg & Bernardet 1991); perch, Perca fluviatilis L.; and roach, Rutilus rutilus (L.) (Madetoja, Dalsgaard & Wiklund 2002). However, the bacterium has never been reported from the sea lamprey and the potential role played by the sea lamprey in the dissemination of the bacterium to cohabitant salmonids has not been addressed. In the Great Lakes basin, sea lamprey, Petromyzon marinus L., has been called the most destructive of invasive species (Lupi & Hoehn 1998). Adult parasitic sea lamprey have been incriminated as a major factor contributing to the collapse of the lake trout, Salvelinus namaycush (Walbaum), and the lake whitefish, Coregonus clupeaformis (Mitchill), fisheries in the Great Lakes during the early 1940s and 1950s (Smith & Tibbles 1980). To reduce the number of sea lamprey and limit its spread, the Great Lakes Fishery Commission began a largescale programme based on male sterilization and release to compete with fertile males during spawning. Males are collected from different sites at Lake Ontario, transported into a sterilizing facility in Hammond Bay, Michigan, and then released into selected river systems basin-wide. These relocation procedures may transfer various pathogens among different fish populations, which Journal of Fish Diseases 2006, 29, 629–632

Viral haemorrhagic septicaemia virus (VHSV) was isolated from muskellunge, Esox masquinongy (Mitchill), caught from the NW portion of Lake St Clair, Michigan, USA in 2003. Affected fish exhibited congestion of internal organs; the inner wall of the swim bladder was thickened and contained numerous budding, fluid-filled vesicles. A virus was isolated using fish cell lines inoculated with a homogenate of kidney and spleen tissues from affected fish. Focal areas of cell rounding and granulation appeared as early as 24 h post-inoculation and expanded rapidly to destroy the entire cell sheet by 96 h. Electron microscopy revealed virions that were 170-180 nm in length by 60-70 nm in width having a bullet-shaped morphology typical of rhabdoviruses. The virus was confirmed as VHSV by reverse transcriptase-polymerase chain reaction. Sequence analysis of the entire nucleoprotein and glycoprotein genes revealed the virus was a member of the North American genotype of VHSV; however, the isolate was sufficiently distinct to be considered a separate sublineage, suggesting its origin may have been from marine species inhabiting the eastern coastal areas of the USA or Canada.

Ichthyophthiriasis (white spot) is one of the economically important diseases affecting almost all freshwater fish and causing outbreaks associated with devastating losses. An outbreak of white spot occurred in an aquaria holding Siamese shark (Pangasius sutchi) and goldfish (Carassius auratus). Initial observation of the outbreak showed that only P. sutchi was affected with typical UP white spots associated with mortalities. However, C. auratus, a known susceptible species for Ich, in the same aquarium showed only mild erythema that disappeared during the course of infection with no mortalities. An experimental infection with Ichthyophthirius multifiliis was induced in P. sutchi and cohabitation was performed with the infected fish and naive P. sutchi and C. auratus to investigate the variation between the two species. Pangasius sutchi showed typical clinical signs with mortalities while cohabitant C. auratus showed only mild erythema without mortalities. Histopathological examination was performed to evaluate the infection variation. The study provides clinical evidence of the potential presence of more than one strain of I. multifiliis of different species specificity.

Bacterial kidney disease (BKD), caused by Renibacterium salmoninarum, is a widespread problem with major implications for salmonid fish species. The mechanisms by which the bacterium has reached high levels of infection previously unrecorded in the Laurentian Great Lakes are presently unknown. Research involving reservoirs and mechanisms of R. salmoninarum transmission in fish is lacking because of the ecologic complexity of heterogeneous habitats and the lack of adequate funding. Herein, we report on the isolation of R. salmoninarum from the kidneys of the sea lamprey (Petromyzon marinus). The bacterium was cultured from kidneys of 16% and 4% of lampreys collected from two locations within the Lake Ontario watershed in 2003 and 2004, respectively. The identity of bacterial colonies was verified with the nested polymerase chain reaction and quantitative enzyme-linked immunosorbent assay.

Ornamental fish constitute an expanding sector of fish industry in Egypt. Several native, naturalized and exotic fish species are known to be raised by fish hobbyists. Among freshwater aquarium fish, goldfish (Carassius auratus) is considered among the most popular and expensive fish species (70 LE per adult fish retail prize). Apart from its importance as an aquarium fish, goldfish presents a problem due to its likelihood role in disease transmission for native and naturalized cyprinid fish in Egypt. This has invigorated the interest to examine imported fish species and study their role in transmission of diseases to other fish species in Egypt. Most recently, a disease with a substantial morbidity and low mortality rate has been identified among imported capped breeds of goldfish. The affected fish showed whitish nodules in the cap region of the head. Upon examination, the nodule oozed milky fluid, leaving hemorrhagic lesions that were refilled with milky fluid 1-2 weeks later. Erosion and ulceration have been reported in some fish during late stages of the disease. Dermocystidium spp. has been associated with the disease and detected in the nodules and milky fluid. The clinical signs of the disease, some epizootiological data, parasite morphology and the histopathological criteria of the lesions are detailed in the present study.

Biochemical characterization of the extracellular proteins (ECP) of two softshell clam Perkinsus spp. cloned isolates, Perkinsus chesapeaki isolate G-117 and Perkinsus marinus H-49, was performed and compared to that of the oyster-derived P. marinus isolate P-1. G-117 and H-49 demonstrated distinct differences in enzyme activities; however, all three isolates shared common bands. Substrate-impregnated gels showed H-49 to possess proteolytic activities while G-117 did not. Inhibition studies revealed that H-49 ECP contain serine proteases similar to those described for P-1. The G-117 ECP lacked proteolytic activity but showed a higher production of lipolytic enzymes than H-49 or P-1. Optimal in vitro growth temperatures for the two clam isolates were generally lower than those for P-1. G-117 showed faster growth at lower salinities than either H-49 or P-1. Clam Perkinsus spp. isolates appear to be better adapted to lower salinities and temperatures than the P. marinus isolate of the eastern oyster.

A gill-associated Perkinsus sp. isolated from the softshell clam (Mya arenaria) is described as a new species, P. chesapeaki sp. nov. Examination of the parasite in seawater cultures revealed life cycle stages and zoosporulation processes similar to those described for other species of the genus Perkinsus. Prezoosporangia developed thickened cell walls upon contraction of the cytoplasm and development of a distinctive clear area between the cell wall and the protoplast. Successive bipartition of the protoplast led to the formation of hundred's of zoospores within mature sporangia. Zoospores were released into seawater through one or more discharge tubes. Ultrastructural studies revealed an oblong zoospore possessing two flagella that arose from a concave side located in the upper third of the zoospore body. The anterior flagellum possessed a unilateral array of hair-like structures. A large anterior vacuole and basolateral nucleus dominated the cytoplasm of the zoospore body. The presence of a rudimentary apical complex including an open-sided conoid, rhoptries, micronemes, and subpellicular microtubules were also discerned. Differences in zoospore morphology, and sequence analyses of two genes previously reported, support the designation of the gill-associated Perkinsus from the softshell clam as a new species.

Despite the ecologic and economic significance of the softshell clam (Mya arenaria), little is known about the humoral factors involved in its host defense mechanisms. Protease inhibitors, a group of proteins believed to play a role in host defense mechanisms against infections and proliferative diseases, have recently been identified in bivalve molluscs. In the present study we provide evidence for the presence of protease inhibitors in softshell clam plasma. Levels of protease inhibitory activities against the enzymes tested varied greatly, e.g. 1 μg of plasma protein inhibited 35.3±9.69 ng pepsin (aspartic protease), 4.9±1.45 ng papain (cysteine protease) and 3.1±0.88 ng trypsin (serine protease). On the contrary, the level of anti-metalloprotease (thermolysin) activities was much lower. The sensitivity to methylamine and the ability to protect trypsin from active site trypsin inhibitors provided evidence for the presence of an α2-macroglobulin-like molecule in softshell clam plasma. In the Chesapeake Bay widespread epizootics of disseminated sarcoma have been described in M. arenaria populations. The impact of this lethal proliferative disorder on clam defense responses has received little attention. In this study the effects of sarcoma progression on plasma protease inhibitory activities were, therefore, assessed. Clams with early stages of sarcoma showed a non-significant decrease in protease inhibitor levels. Clams with advanced stages of sarcoma showed a significant decrease in the ability to inhibit trypsin and papain, while the protease inhibitory activity levels against aspartic and metalloprotease were completely exhausted.

Aphanomyces spp. were isolated from skin erosions and ulcers of cultured Striped and thin lip grey mullets. Fungi with non-septated hyphae were found in wet mount preparations of skin. Samples inoculated on glucose peptone liquid medium for three successive steps then mycelial growths were transferred into glucose peptone yeast extract agar medium. Aphanomyces spp. were successfully isolated, in axenic cultures, from seven out of 35 fish samples. The cultures were maintained on glucose peptone yeast extract liquid media. Formation of sporangia in tap water that contained hemp seeds confirmed that the grey mullet isolates are members of tlx genus Aphanomyces. All isolates grew progressively at salinities thar ranged from 2-8 ppt, however, only one isolate survived at 37 degrees C.

Extracellular proteases were isolated from the cell-free culture supernatant of the oyster-pathogenic protozoan, Perkinsus marinus, by bacitracin–sepharose affinity chromatography. The purified protease fractions contained >75% of the protease activity initially loaded onto the column with very high specific activity that corresponded to 8–11-fold level of protease enrichment. The isolated proteases hydrolysed a variety of protein substrates including oyster plasma. All of the isolated P. marinus proteases belonged to the serine class of proteases. Inhibitor studies involving spectrophotometric assay and gelatin gel electrophoresis showed high levels of inhibition in the presence of the serine protease inhibitors PMSF, benzamidine and chymostatin, whereas inhibitors of cysteine, aspartic, and metalloproteases showed little or no inhibition. Spectrophotometric assays involving serine-specific peptide substrates further revealed that the isolated proteases belong to the class of chymotrypsin-like serine proteases. A 41.7 kDa monomeric, N-glycosylated, serine protease (designated Perkinsin) has been identified as the major P. marinus extracellular protease.

The in vitro growth rates of two isolates of Perkinsus marinus were significantly reduced by bacitracin. Upon coincubation with I mg bacitracin/mL, the doubling times rose from 27 +/- 2.1 h to 34 +/- 2.9 h for the LMTX-1 isolate (P < 0.001) and from 15 +/- 1.9 h to 22.2 +/- 2.4 h for the Perkinsus-1 isolate (P < 0.001). At 10 mg bacitracin/mL, viability of both isolates was much reduced (P < 0.0001). The sensitivity of P. marinus to bacitracin was examined in vivo in two clinical trials. In the first, individual eastern oysters Crassostrea virginica were injected with 10(7) Perkinsus-1 cells, then fed bacitracin at a concentration of 5 or 50 mg/mL encapsulated in lipid vesicles daily for 6 weeks. Parasite body burden was significantly reduced in oysters administered 5 mg bacitracin/mL (3.3 x 10(4) +/- 2.5 x 10(4) hypnospores/g wet tissue) or 50 mg/ mt (5.3 x 10(4) +/- 6.4 x 10(4) hypnospores/g) as compared with control oysters (3.2 x 10(5) +/- 4.7 x 10(5) hypnospores/g, P < 0.05) that received encapsulated seawater only. In the second experiment, naturally infected oysters(average, 10.9 x 10(6) +/- 30.7 x 106 hypnospores/g) received encapsulated bacitracin at 10 mg/mL for LO seeks. Treated oysters had significantly lower levels of infection (2.5 x 10(6) +/- 3 x 10(6) hypnospores/g) than did control oysters (67.4 x 10(6) +/- 144 x 10(6) hypnospores/ g, P < 0.05). Despite the sharp decrease in infection intensity in the bacitracin-treated oysters, survival rate improved by only 10%. It is possible that damage to the vital organs of infected oysters was too advanced and widespread to be reversed. The in vitro and in vivo findings of this study suggest that bacitracin has promise for use in P. marinus chemotherapy.