Advances in Detection Techniques for Fungus-like Organisms of Aquaculture Importance

Abstract

Oomycetes are a class of eukaryotic organisms that are similar to fungus in morphology and lifestyle. The cell wall of oomycetes is composed of cellulose, unlike fungus, where chitin is the main component. These organisms are generally considered saprophytes with the ability to cause secondary infection. However, some species are highly pathogenic and cause severe diseases in fish. Important fish pathogens of this class belong to the genus Saprolegnia, Achlya, and Aphanomyces under the order Saprolegniales. These organisms have caused huge economic loss in aquaculture and are even considered responsible for the decline in populations of wild fish and amphibians. Previously, these organisms were effectively controlled by use of malachite green, which was later banned. This has led to the emergence of these organisms with increased incidence, virulence, and host range. The diagnosis of the disease can be made by observing the gross lesion of white cotton wool-like growth at the site of infection, but identifying a causative agent is not possible. Identification of the genus and up to the species level is made through various ways such as microscopic observation of the reproductive structures, antibody-based methods, and molecular identification techniques. With advancement in technology, rapid, specific methods have been developed that can identify as well as quantify the causative agent in a given sample. Fast and accurate identification of pathogen will enable us to act promptly against the infection to prevent further spread.