Incidence of Mycobacteriosis in Young of the Year Striped Bass (Morone saxatilis) from the Chesapeake Bay

Striped bass (Morone saxatilis) in the Chesapeake Bay are experiencing a high occurrence of Mycobacterium spp. infections characterized by high visceral and dermal granulomatous lesions. It has been suggested that mycobacteriosis may be the cause of increased striped bass mortality rates in the Chesapeake Bay. Mycobacteriosis is an epizootic bacterial disease caused by a large group of Mycobacterium spp. The most recent and dominant isolates that have been cultured from Chesapeake Bay striped bass include Mycobacterium marinum, M. shottsii, and M. pseudoshottsii. Previous studies have used techniques such as bacteriology and histology to identify the presence of these isolates. As the fish ages, infection prevalence increases and so many studies have focused on prevalence of mycobacteriosis in adult striped bass rather than in juvenile striped bass. Other studies that have focused on mycobacteriosis in young of the year striped bass have indicated low infection rates. Our study was designed to determine whether striped bass are acquiring mycobacteriosis during their early life stages and to determine whether Mycobacterium spp. infection rates have increased over time using sensitive molecular techniques. Prey items were also tested in order to see if infection was prevalent among adult striped bass forage species. We collected and analyzed 18 young of the year striped bass(Morone saxatilis), 10 white perch (Morone americana), 2 atlantic croaker (Micropogonias undulatus), 1 least killifish (Heterandria formosa) and 1 bay anchovy (Anchoa mitchilli). Samples were analyzed using PCR-RLFP to identify and differentiate Mycobacterium spp. The use of these molecular assays using splenic tissues from each sample indicated the presence of Mycobacterium spp. within one young of the year striped bass and one white perch. Mycobacteriosis was not detected in the remaining 17 young of the year striped bass and other adult striped bass prey items.