Effects of Subclinical Mycobacterium chelonae Infections on Fecundity and Embryo Survival in Zebrafish.

Mycobacteriosis is the second most common infectious disease in zebrafish research colonies, and most often this is caused by Mycobacterium chelonae. The infection is characterized by multiple granulomas in the kidney, coelomic cavity, particularly the ovary. However, most fish still appear clinically normal. Developmental genetics remain a primary area of research with the zebrafish model, and hence, an important use of adult zebrafish is as brood fish to produce embryos. We investigated the effects of experimentally induced M. chelonae infections on fecundity. A total of 480 5D wild-type zebrafish were divided into four groups: controls, males infected, females infected, and both sexes. Exposed fish developed high prevalence of infection, including many females with ovarian infections. Fish were then first subjected to four separate group spawns with four replicate tanks/group. Then, a third of the fish were subjected to pairwise spawns, representing 20 pairs/group, and then the pairs were evaluated by histopathology. Overall, the group and pairwise spawns resulted numerous eggs and viable embryos. However, we found no statistical correlations between infection status and number of eggs or viability. In contrast to Egg Associated Inflammation and Fibroplasia, lesions in infected ovaries were more localized, with large regions of the ovary appearing normal.