Branchiomyces Demigrans Infection in Farm‐Reared Common Carp (Cyprinus Carpio L.) and Nile Tilapia (Oreochromis Niloticus) at Different Localities in Egypt, With Special Emphasis to the Role of Environmental Stress Factors

Several cases of branchial mycosis caused by Branchiomyces spp. were identified in fingerlings specimens of Nile tilapia(Oreochromis niloticus) and Common carp(Cyprinus carpio)which obtained from different 4 private farms at Damietta, Port-said, El-Behera and Kafr-El Sheikh governorates, Egypt during the summer of 2014.Mortalities ranged from a few hundred to several thousand fish per pond. Significant gross and histopathological findings from these cases were limited to the gills. The infected fishes were suffering from respiratory distress; gasping air from the water surface and rapid movement of opercula. Squash preparations from the infected gill tissue revealed brown, broad, branched and non-septated hyphae. On Sabouraud's dextrose agar (SDA) media with 10% duck decoction showed bright white colonies after 2 days which reached its maximum growth 8 days post inoculation. Microscopical examination of stained growth with lactophenol cotton blue, branched hyphae at their tips were identified which were characteristic for Branchiomyces sp. The causal pathogen was identified as Branchiomyces demigrans, in which the diameter of spores and non-septated hyphae were 4-10μm and 16-24μm respectively. Histopathological examination from infected fish gills revealed that all examined fishes had fungal mycelia that were mainly but not entirely confined to the base of the primary lamellae and the gill arches. These fungal hyphae were intravascular and occluded vessels in the gill tissues. It was found that ammonia, nitrite and organic matter were elevated over the permissible levels in the surveyed localities. The present paper describes the fungal characteristics and pathology of branchial mycosis caused by Branchiomyces spp. in these freshwater fishes and the relation of Branchiomyces infection with water quality parameters.

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