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Journal Entry   Back Delaware Bay striped bass mycobacteriosis study Northeast Region, March 31, 2005 Print Friendly Version Completed a study on the prevalence of mycobacteriosis in Delaware Bay striped bass in conjunction with the USGS National Fish Health Research Laboratory. Mycobacteriosis is a bacterial disease that occurs in a large number of fish species including striped bass (Morone saxatilis). Diseased striped bass exhibit visceral and/or skin lesions with substantial disfigurement resulting from the latter. Emaciation may also be observed in severely diseased fish. While the extent of mortality associated with mycobacteriosis in wild striped bass is not fully understood, laboratory studies indicate that at least one of the mycobacterial species isolated from Chesapeake Bay striped bass can cause lethal infections when administered in biologically relevant doses. In many regions of the United States, striped bass are a highly prized target species for recreational anglers and commercial fishermen. The economic impact of striped bass devalued as a result of mycobacteriosis is equal in significance to dead fish because emaciated or disfigured fish have no market value. Moreover, infected fish pose a human health risk to persons that directly handle the fish, including anglers and those involved with commercial harvesting and processing. To date, much of what is known of mycobacteriosis in wild striped bass is based on data from fish collected in the Chesapeake Bay and its? tributaries. The on-going epizootic in Chesapeake Bay striped bass has produced focal points with high infection rates in association with substantial pathology. In order to determine the prevalence of mycobacteriosis in Delaware Bay, the estuary to the north of Chesapeake Bay, a preliminary study was initiated in 2003 to determine if mycobacteriosis is occurring in Delaware Bay striped bass. Eighty striped bass were obtained from commercial gill-nets off Woodland (n = 70) and Bowers (n = 10) Beach in December of 2003. Data obtained from these samples were compared to those obtained in November 2003 from striped bass captured in pound nets located in the Chesapeake Bay at the mouths of the Potomac (n = 50) and Nanticoke Rivers (n = 50). Tissues were examined for the presence of mycobacteria, non acid-fast bacteria and associated pathology. Pooled data from Delaware Bay indicated an overall infection rate (number of infected fish of approximately 17% and an infection intensity (mean+-SE) of 3.398 +- 0.576 Log CFU g-1 of spleen in the infected striped bass. Infection rates in Delaware Bay were significantly lower (p < 0.025) than those observed at the Chesapeake Bay sites where the rates were 80.4% and 60.4% for the Potomac and Nanticoke Rivers respectively. Infection intensity in impacted striped bass was significantly lower than observed in the Potomac but not the Nanticoke River where the infection intensities (mean +-SE.) were 5.054 +-0.318 and 4.772 +- 0.384 respectively. Disease (mycobacteriosis), as indicated by the presence of granulomas containing acid-fast bacilli in the tissues, was observed at low rates ( ~ 6 %) and at low levels in impacted individuals (1-3 granulomas per tissue section with no recrudescence). Mycobacteria-associated skin lesions, a major concern in Chesapeake Bay striped bass, were not observed in the Delaware Bay samples. The fish were in good condition overall with only one sampled fish exhibiting a relatively heavy infection (over 10,000 CFU g-1 of spleen). The isolate from this heavily infected fish, identified as Mycobacterium chelonae based on phenotypic characteristics, was the only isolate to clearly fit current species descriptions. Mycobacterium chelonae has been widely reported from fish and is a human pathogen. Other isolates appear to be similar to recently described species obtained from Chesapeake Bay striped bass. Although the data from this preliminary study suggests that the rate and severity of mycobacterial infection in the sampled Delaware Bay striped bass is low relative to that observed in Chesapeake Bay, the study involves a small number of fish thus extrapolations from the data sets should be made with caution. The data indicate that striped bass infected with mycobacteria are present in Delaware Bay and that the infection rate and intensity should be monitored to identify any significant disease or mortality that may be attributed to mycobacteria. Contact Info: Jennifer Lapis, (413) 253-8303, jennifer_lapis@fws.gov Send to: From: Notes: ..........................................................................................

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