Which of the following parasites is most commonly associated with skin and gill infections in marine fish?

The correct choice is related to the Capsalids, which are flatworms belonging to the family of Monogenea. Capsalids are known to primarily infect the skin and gills of marine fish, causing significant health issues. They can attach themselves to the surfaces, leading to lesions, irritation, and secondary infections as a result of their feeding practices. They are often unfortunately referred to as "gill flukes" due to their specific predilection for gill infection.

Understanding the habitat and infection sites of various parasites helps clarify why Capsalids are especially relevant in marine environments. The physical presence of these parasites on the gills and skin can directly impact respiratory efficiency and overall wellbeing in fish, leading to deteriorated health and increased susceptibility to other pathogens.

In contrast, Dactylogyrus and Gyrodactylus are more typically associated with freshwater fish. Dactylogyrus predominantly affects the gills, while Gyrodactylus can affect the skin and gills as well but is primarily found in freshwater systems. Mycobacterium, while it can cause significant issues in fish, leads to systemic infections and lesions, which are not exclusively tied to the skin and gill like Capsalids. This distinction in