Abstract
Despite increasingly sophisticated microbiological techniques, and long after the first discovery of microbes, basic knowledge is still lacking to fully appreciate the ecological importance of microbial parasites in fish. This is likely due to the nature of their habitats as many species of fish suffer from living beneath turbid water away from easy recording. However, fishes represent key ecosystem services for millions of people around the world and the absence of a functional ecological understanding of viruses, prokaryotes, and small eukaryotes in the maintenance of fish populations and of their diversity represents an inherent barrier to aquatic conservation and food security. Among recent emerging infectious diseases responsible for severe population declines in plant and animal taxa, fungal and fungal-like microbes have emerged as significant contributors. Here, we review the current knowledge gaps of fungal and fungal-like parasites and pathogens in fish and put them into an ecological perspective with direct implications for the monitoring of fungal fish pathogens in the wild, their phylogeography as well as their associated ecological impact on fish populations. With increasing fish movement around the world for farming, releases into the wild for sport fishing and human-driven habitat changes, it is expected, along with improved environmental monitoring of fungal and fungal-like infections, that the full extent of the impact of these pathogens on wild fish populations will soon emerge as a major threat to freshwater biodiversity.
Highlights
Fishes are susceptible to diseases caused by a large number of infectious agents including viruses, bacteria, true fungi, fungallike microrganisms, other protists, and metazoans
The number of reported fungal and fungal-like pathogens responsible for diseases in animals is on the increase globally (Fisher et al, 2009; Holdich et al, 2009; Loo, 2009; Frick et al, 2010; Ratnieks and Carreck, 2010; Sarmiento-Ramírez et al, 2010)
Increasingly infectious outbreaks are reported in a broad range of species from coral (Kim and Harvell, 2004) to wheat (Wanyera et al, 2006); notable examples include local extinctions of bats (Frick et al, 2010), bees (Ratnieks and Carreck, 2010), turtles (Sarmiento-Ramírez et al, 2010), amphibians (Fisher et al, 2009) and fish (Gozlan et al, 2005, 2009)
Summary
Fishes are susceptible to diseases caused by a large number of infectious agents including viruses, bacteria, true fungi, fungallike microrganisms, other protists, and metazoans. In aquatic ecosystems fungi and fungal-like pathogen detection in fish hosts is more complicated due to the lack of direct observation of their hosts contrary to frogs or coral, for example (Gozlan, 2012) This is true in freshwater systems where, despite being responsible for pan-continental population extinctions, some diseases caused by fungal and fungal-like pathogens are chronic with no clear external symptoms (Gozlan et al, 2005; Kocan and Hershberger, 2006; Andreou et al, 2011, 2012). This could involve simple one host – one pathogen challenges such as in Andreou et al (2012) or a Frontiers in Microbiology | Aquatic Microbiology
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