Experimental infection of Aphanomyces invadans and susceptibility in seven species of tropical fish.

Mohd Daud Hassan Hj.,Mohammad Afsharnasab,Issa Sharifpour,Shiv Shankar,Seyedeh F. Afzali

doi:10.14202/vetworld.2015.1038-1044

Abstract

Aim:Epizootic ulcerative syndrome (EUS) causes by aquatic oomycete fungus, Aphanomyces invadans is a dangerous fish disease of a wide range of fresh and brackish water, wild and farmed fish throughout the world. The objective of the present study was to determine the susceptibility of a number of tropical fish species to the EUS and compare the severity of infection between experimental groups.Materials and Methods:Snakehead, Channa striata (Bloch, 1793); snakeskin gourami, Trichopodus pectoralis (Regan, 1910); koi carp, Cyprinus carpio (Linnaeus, 1758); broadhead catfish, Clarias macrocephalus (Günther, 1864); goldfish, Carassius auratus (Linnaeus, 1758); climbing perch, Anabas testudineus (Bloch, 1792); and Nile tilapia, Oreochromis niloticus (Linnaeus, 1758) were challenged by intramuscular injection using zoospores of Aphanomyces invadans (NJM9701). The infected fish skins and muscles were examined for EUS histopathological characteristics, and the results on the severity of lesions and mortality were analyzed using SPSS program.Results:All zoospore-injected fish were shown to be susceptible to the EUS infection except Nile tilapia. Although, the general histopathological pattern was similar in the zoospore-injected group, but there were some variation in granulomatous reaction, that is the presence or absence of giant cells, and time of mortality were detected. The result of statistical analysis showed that there was a significant difference between species, (c2=145.11 and p<0.01).Conclusion:Gourami, koi carp, and catfish were demonstrated to be highly susceptible while goldfish and climbing perch were found to be moderately susceptible to the EUS infection. These findings suggested that the cellular response of fish to mycotic infection and granulomatous reaction varied in different fish species, which could not be an indicator of susceptibility or resistant to the EUS itself, although it was shown that the granulation rate and the level of maturity or solidification (consolidation of granulomas) were higher in resistant fish.

Highlights

Epizootic ulcerative syndrome (EUS) is a clinical fish condition that arguably had the most serious socio-economic impact affecting the fresh and brackish water fish over the past 40 years and has been listed by the Aquatic Animal Code since 1995 [1]
Gourami, koi carp, and catfish were demonstrated to be highly susceptible while goldfish and climbing perch were found to be moderately susceptible to the EUS infection
These findings suggested that the cellular response of fish to mycotic infection and granulomatous reaction varied in different fish species, which could not be an indicator of susceptibility or resistant to the EUS itself, it was shown that the granulation rate and the level of maturity or solidification were higher in resistant fish

Summary

Introduction

Epizootic ulcerative syndrome (EUS) is a clinical fish condition that arguably had the most serious socio-economic impact affecting the fresh and brackish water fish over the past 40 years and has been listed by the Aquatic Animal Code since 1995 [1]. The disease propagates through the countries of the Asia-Pacific region with dire consequences for fish resources and the livelihood of fishermen [2]. EUS is a disease that manifests in acute skin and muscle ulceration with the consequence of significant mortality in freshwater fish. The aquatic oomycete fungus, Aphanomyces invadans, has been identified as the causative agent of EUS [3,4] which releases a proteolytic enzyme facilitating penetration of fish tissue and precipitating shallow to deep ulcers, leading to a high mortality in fish population [5].

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