bassianolide and Skin-Ulcer

The hybrid grouper, Epinephelus fuscoguttatus (♀) × Epinephelus lanceolatus (♂), is a newly bred cultivated marine fish species of high economic value. However, a skin ulcer disease with high mortality has occurred, and the responsible pathogen remains unknown. In this study, we summarized the epidemic status and external signs of this disease. We screened potential pathogens and finally isolated one bacterial strain ML01 from affected fish. We subjected healthy juvenile hybrid groupers to bacterial challenge tests with the isolate by immersion, immersion after dermal abrasion and intraperitoneal injection, respectively. Within 14 days post-infection, the isolate ML01 caused mass mortality of juveniles infected via immersion after dermal abrasion or intraperitoneal injection. Diseased juveniles displayed obvious signs of skin ulcers. The median lethal dose of ML01 by intraperitoneal injection was 1.10 × 10

Topics: Animals; Bass; Fish Diseases; Hybridization, Genetic; Phylogeny; Sequence Analysis, DNA; Skin Ulcer; Vibrio; Vibrio Infections; Virulence

In a previous study, we discovered that acute confinement stress causes rapid ulceration of the fins of hybrid striped bass Morone saxatilis female x M. chrysops male (Noga et al. 1998. Vet Pathol 35:102-107). In this paper, we report the development of a reproducible model for studying this phenomenon in juvenile hybrid striped bass. We also determined how quickly ulceration could develop in acutely stressed fish and documented the sequential light microscopic and ultrastructural changes associated with this response. When hybrid striped bass were subjected to a standardized confinement protocol, the pathological response was extremely rapid (fin ulceration began to develop within 15 min of confinement). Grossly, the distal edges of the fins became blanched, and melanophores aggregated near the basement membrane and dermis after 15 min of confinement. Microscopically, the earliest detectable change in the fins, which occurred within 15 min of confinement, was swelling and loss of microridges of the outermost epidermal cells; this was followed by epidermal erosion. After 30 min of stress, epidermal ulceration developed at the distal edges of the fins. At this time, both necrotic and apoptotic epidermal cells were present. The middle and basal epidermal layers were severely spongiotic and the dermis and hypodermis were edematous. Over longer periods (up to 2 h), lesions were similar but increasingly more severe, progressing from the distal edge of the fin towards the base. The response to acute stress showed a significant correlation between confinement period and severity of the pathological changes (epidermal degeneration, epidermal ulceration and leukocyte infiltration). Also, we demonstrated that epidermal damage was not restricted to the fins but also affected the body skin and eyes. The ventral area of the body and the corneal epithelium of stressed fish were ulcerated; however, skin on the head and operculum was not affected, suggesting a site-specific mode of damage. In stressed fish, epidermal ulceration was found in 67 to 97% of all fins, 88% of skin on the ventrum, and 67% of corneas, while control fish had only very mild epidermal ulceration in the few fish in which it was present (on 5 to 10% of the fins, but not on the ventral skin or corneas). Due to the widespread damage to epidermal tissues of the body surface, we have named this the acute ulceration response (AUR). Our study indicates that acute confinement can rapidly cause significant d

Topics: Analysis of Variance; Animals; Bass; Crowding; Epidermis; Fish Diseases; Histological Techniques; Microscopy, Electron, Transmission; Skin Ulcer; Stress, Physiological; Time Factors

There is a need to develop simple, rapid, and accurate methods for assessing health in fish populations. In this study we demonstrate that use of fluorescein, a nontoxic fluorescent dye, can rapidly and easily detect the presence of skin ulcers in all fish tested, including rainbow trout (Oncorhynchus mykiss), channel catfish (Ictalurus punctatus), goldfish (Carassius auratus), and hybrid striped bass (Morone saxatilis male X M. chrysops female). Exposure of fish to as little as 0.10 mg fluorescein per milliliter of water for 3 minutes was sufficient to identify experimentally induced lesions, even pinpoint ulcerations. Such lesions were not visible to the naked eye but were clearly demarcated with fluorescein treatment. Examination of fish that appeared clinically normal often revealed the presence of focal ulcerations, which might have been a consequence of damage during capture, but it also might suggest that skin ulceration may be common even in "clinically normal" fish. Exposure of either nonulcerated or experimentally ulcerated hybrid striped bass to an excessively high concentration of fluorescein had no apparent effect on health or survival. Our studies suggest that fluorescein may be a highly useful tool for rapid health screening in fish populations.

Topics: Animals; Aquaculture; Bass; Female; Fish Diseases; Fluorescein; Fluorescent Dyes; Goldfish; Ictaluridae; Male; Oncorhynchus mykiss; Photography; Skin Ulcer; Stress, Physiological

Exposure of striped bass (Morone saxatilis) and hybrid bass (M. saxatilis female x Morone chrysops male) to an acute (2-hour) confinement stress caused skin ulceration on the fins but not on the body of all confined fish. Striped bass displayed more severe lesions than did hybrid bass. Histologically, lesions had varying degrees of epithelial erosion and ulceration, which was most severe at the distal portion of the fins. Ulceration was associated with dermal and hypodermal edema and necrosis of the remaining stromal tissue and tips of bone in the fin rays. No hemorrhage or thrombosis was present to suggest any obvious vascular derangement. No evidence was found for either trauma or an infectious agent initiating the lesions. Injecting fish with epinephrine caused a similar response, although the degree of ulceration was less severe. These findings may explain why many opportunistic skin pathogens can rapidly develop into serious infections in fish.

Topics: Animals; Bass; Colony Count, Microbial; Crosses, Genetic; Crowding; Epinephrine; Fish Diseases; Immunity, Innate; Incidence; Opportunistic Infections; Skin Ulcer; Stress, Physiological

Edwardsiella tarda, an opportunistic bacterial pathogen, was isolated from dying largemouth bass (Micropterus salmoides) during an epizootic in a eutrophic lake system, Lochloosa Lake, Florida, USA. Approximately 1,500 adult fish died over a 6-wk period during the late summer and early fall of 1991. A mixed population of aerobic bacteria (E. tarda, Aeromonas hydrophila, and Pseudomonas sp.) was isolated from deep cutaneous ulcers and intestines of moribund bass. However, E. tarda in pure culture was the only bacterium isolated from several viscera of several fish; E. tarda may be the etiologic agent responsible for some episodes of seasonal mortality in largemouth bass.

Topics: Animals; Bass; Disease Outbreaks; Enterobacteriaceae; Enterobacteriaceae Infections; Female; Fish Diseases; Florida; Fresh Water; Seasons; Skin Ulcer; Viscera