Fungal Diseases in Fish

Fungal diseases of fish have become increasingly important, over the past 20 years. The traditional ‘‘fungi’’ are comprised of members from several different taxonomic kingdoms. An increasing number of other environmental fungi are being reported from diseased fish, further testament to the opportunistic nature of many fungi. Active fungal agents living in waters cause infections in juvenile and adult individuals in fish populations, leading to decay in eggs and larvae. Fungal infections that are generally observed as a secondary infection in fish populations become established in lesions caused as a result of mechanical injury by bacterial, viral, and parasitic primary agents, consequently causing a change in the prognosis of the disease. Fungi, however, can cause disease under a variety of other circumstances. Some may be more aggressive and play a more primary role. Fungi can be external or internal, and systemic. Fungi can cause problems during reproduction, for example, by infecting fertilized eggs in spawns. Certain species of fungi can grow in poorly stored feeds and produce mycotoxins. Fungal diseases, in general, are very difficult to control or treat once they have taken hold. Prevention is, as always, the best medicine. Increased knowledge of basic biology will help guide treatment and control methods. This review study sought to provide insights into the fungal diseases of wild or farmed fish introduced onto the market.