The implication of specific nutrients in the development of many musculoskeletal deformities is complicated by the multifactorial nature of their pathogenesis, however, the importance of several key nutrients is unquestionable. There are numerous causes of myositis due to infectious agents where the musculoskeletal system is secondarily affected. This chapter explains only a few key pathogens that notably and consistently target the musculoskeletal system. Edwardsiellosis affects a range of fish species in freshwater and marine environments around the world, and is particularly common in warm water. The cartilage of the branchial arches and cranium are the primary targets in cephalic osteochondritis with lysis, pyogranulomatous inflammation and often some degree of fibrosis if the fish survives. Bacterial kidney disease caused by Renibacterium salmoninarum is one of the most important infectious diseases that significantly affects muscle. Renibacterium salmoninarum is a Gram-positive diplobacillus that belongs to the Micrococcus-Arthrobacter sub-group of the actinomycetes.