Reduced swimming performance in delta smelt infected with Mycobacterium spp.

Delta smelt Hypomesus transpacificus infected with Mycobacterium spp. swam significantly more slowly (mean ±s.e., 24±5 ± 1·2 cm s −1) than uninfected fish (30·0 ± 1·7 cm s −1). Differences in swimming performance were not attributable to differences in fish size (Ls or wet mass), condition factor or laboratory holding duration. Similar proportions of non‐fatigue‐related swimming failure among the uninfected and infected fish indicated that mycobacteriosis did not affect the willingness of delta smelt to swim in the flume. Level of infection, measured for the dominant M. chelonae pathogen using enzyme‐linked immunosorbent assay (ELISA), did not affect critical swimming velocity.