Histopathology of snakehead, Channa striatus (Bloch), experimentally infected with the specific Aphanomyces fungus associated with epizootic ulcerative syndrome (EUS) at different temperatures

Abstract

Snakeheads, Channa striatus (Bloch), were inoculated with a spore suspension of the specific pathogenic Aphanomyces, isolated from fish affected by epizootic ulcerative syndrome (EUS), in South East Asia. Fish were held at three different temperatures: 19, 26 and 31 °C. Histological changes induced by the infection are described. In the early stages of the disease, degenerative changes were observed in all samples, but inflammatory infiltrate was much more marked in fish kept at 26 and 3i°C. By 8 days post-injection, extensive mycotic granulomatosis was observed in the samples kept at 26 and 31*^0. The fish kept at 19°C developed a severe invasive myonecrosis with limited macrophage response. From 14 to 28 days post-injection, healing became well established at 26 and 3KC and surviving fish kept at these temperatures recovered completely by 28 days.

Emergence of the Epizootic Ulcerative Syndrome in Pond Reared Carp Fish (Cyprinids) and It's Control Measure in Chitwan, Central Nepal

“…Losses due to EUS are difficult to estimate because of its widespread occurrence in many countries and inadequacy of record keeping. Thailand indicated losses in catfish and snakehead culture amounting to US$8.7 million in 1982US$8.7 million in -1983 outbreaks (Chinabut, 1994). In Bangladesh, the losses in fish mortality amounted to about US$5.6 million (ADB/NACA, 1991).…”

“…In Bangladesh, the losses in fish mortality amounted to about US$5.6 million (ADB/NACA, 1991). A number of comprehensive reviews on economic loss and impact aspect of EUS were reported (Roberts et al, 1993;Noga, 1993;Chinabut, et al, 1995;Roberts, 1997;Chinabut, 1998;Lilley et al 1998), besides EUS has listed by the Network of Aquaculture Centers in Asia-pacific (NACA) and internationally by the World Organization for Animal Health (Office International des Epizooties or OIE) (AFFA, 2000;FAO, 2009;Pradhan et al, 2014).…”

“…Water quality variable monitored at the time of fish sampling were not below acceptable trigger values for aquatic ecosystems. Though temperature is a critical factor determining the severity of EUS outbreaks and most mortalities occur when water temperatures are relatively low (Chinabut et al, 1995). Low water temperatures (<16 o C) and rapid decreases in temperature are immunosuppressive and induce changes to the epidermis including loss of mucus that induce changes to the epidermis, including loss of mucus that predispose fish to infection (Bly and Clem, 1992;Quiniou et al, 1998).…”

Horizontal transmission of epizootic ulcerative syndrome (EUS)-associated virus in the snakehead Ophicephalus striatus under simulated natural conditions

“…Previous studies also confirmed the presence of A. hydrophila in Laguna de Bay waters (Lio-Po et al 1992), the site of the present study. Moreover, cytotoxin-producing strains of A. hydrophila were associated with EUS-affected fish and hypothesized to play an important role in the pathogenesis of the disease by Yadav et al (1992).In challenge experiments, the pseudofungi Aphanomyces invadans induced red hemorrhagic lesions at the site of injection of most experimental snakeheads at 19 and 26°C, with granuloma development at the latter higher temperature, while fish at the lower temperature showed acute inflammation (Chinabut et al 1995). Roberts et al (1993) and Lilley & Roberts (1997) showed that EUS-associated Aphanomyces sp.…”

Pathogenicity of the Epizootic Ulcerative Syndrome (EUS)-Associated Rhabdovirus to Snakehead Ophicephalus striatus.

“…However, studies have shown that a rhabdovirus, the bacteria, Aeromonas hydrophila and the fungus Aphanomyces have been consistently associated with EUS-affected snakehead O. striatus (Frerichs et al, 1986;Lio-Po et al, 1992;Rob erts et al, 1993;Callinan et al, 1995). So far, none of these pathogens have been conclusively proven to be the primary agent of EUS (Frerichs et al, 1993;Chinabut et al, 1995 Viral effects on different size groups Different size groups of naive snakeheads consist ing of fingerlings (two size groups) and fry were exposed to virus isolate 95-96 by bath. Three replicates of 10 fingerlings/aquarium and the same number of replicates of 20 fry/aquarium were immersed in a viral suspension (105 TCID50/mL) for 1 h then diluted to 5 L (a five-fold dilution).…”