Mycobacterial infections in striped bass from Delaware Bay

Eighty striped bass Morone saxatilis were obtained from Delaware Bay using commercial gill nets set adjacent to Woodland Beach (n = 70) and Bowers Beach (n = 10) in December 2003. Fish were examined for gross lesions. Total lengths (TLs) and eviscerated weights were determined to calculate condition factors (K). Portions of spleens were aseptically harvested for bacterial culture, and portions of spleens, kidneys (anterior and posterior), livers, and gonads were obtained for histological examination. The size distribution of the striped bass was relatively homogeneous; the mean TL was about 600 mm for all samples. Mean K exceeded 0.95 in all samples and was not significantly different (P > 0.05) among samples. Significant differences in mycobacterial infection prevalence (P ≤ 0.05) were observed among samples; samples obtained at Woodland Beach (WB) on December 10 (53.8%, n = 13) and December 17 (7.1%, n = 42) exhibited the most striking differences in prevalence. Mycobacterial infection intensity ranged from 1 × 10² to 1 × 10⁷ colony-forming units per gram of spleen. Acanthocephalan infection prevalence and intensity, non-acid-fast bacterial infection prevalence, and fish sex ratio were also significantly different among the samples (P ≤ 0.05). Similar to the mycobacterial infections, differences in sex ratio, acanthocephalan infection, and non-acid-fast bacterial infection were observed between the WB samples taken on December 10 and 17. However, no significant associations (P > 0.05) were observed between sex ratio or these infections and mycobacterial infection. The differences in bacterial and parasite infection prevalence and intensity and fish sex ratio in some samples indicate that these fish had a different history and that the epizootiology of mycobacterial infection in striped bass from Delaware Bay may be relatively complex.