Disseminated infection due to Exophiala pisciphila in Cardinal tetra, Paracheirodon axelrodi

Abstract

Cardinal tetra, Paracheirodon axelrodi (Schultz, 1956), kept in an ornamental tank, was found to be affected by severe invasive mycosis. Externally, the disease manifested as abdominal swelling, and internally, the anterior part of the intestine was extremely bloated with abundant dematiaceous septate hyphae and an accumulation of fluid. Histopathologically, a granulomatous inflammatory response was observed in the intestine wall, kidney and spleen. We assume that the mycotic agent was primarily deposited in the intestine and was then gradually disseminated to the other organs. DNA sequencing of ITS and LSU rDNA regions and phenotypic characterization were used for identification of the isolated fungus. The obtained data confirmed that the infection was caused by Exophiala pisciphila. The disease was subsequently reproduced in the carp fingerling using intramuscular and intraperitoneal injection of a spore suspension. The 13th day after intramuscular infection, a marked elevation of neutrophils was recorded in the peripheral blood; this involved a proliferation of band forms and segmented forms. As far as we know, this is the first report of infection due to E. pisciphila in Cardinal tetra.

Swim bladder mycosis in pretty tetra (Hemigrammus pulcher) caused by Exophiala pisciphila and Phaeophleospora hymenocallidicola, and experimental verification of pathogenicity

“…Little is known about changes in the haematology and biochemistry of blood plasma during fungal infection, although these diagnostic methods can be helpful in assessing fish health in intensive aquaculture. In line with the results of our experimental testing of the pathogenicity of E. pisciphila in common carp (Řehulka et al., ), we also recorded an increase in neutrophil band forms and segmented forms in rainbow trout. A similar finding was reported by Qureshi, Chauhan, and Mastan (), who described an increased occurrence of granulocytes in four freshwater fishes in India infected with the oomycetes Achlya prolifera , Aphanomyces sp., Dictyuchus monosporus and Saprolegnia parasitica , and in a study by Jamalzadeh, Keyvan, Ghomi, and Gherardi () in Caspian salmon ( Salmo trutta caspius ) affected by saprolegniasis.…”

“…The confined space of an aquarium is prone to the accumulation of, and therefore increased concentrations of, fungal propagules continuously mobilized from the mentioned reservoirs. In a previous study on Paracheirodon axelrodi infected with E. pisciphila , we observed fungal hyphae in the gastrointestinal tract, which suggests that there were two possible routes of infection from an exogenous source: one was via the alimentary tract, where infective stages of the fungus pass across the intestinal mucosa and are subsequently disseminated to visceral organs, while the other route was via the accumulation of spores in the swim bladder via the pneumatic duct (Řehulka et al., ). In line with the earlier findings, we found an inflammatory response in the intestinal wall and in the kidney, and we also observed exophthalmia, which was described by Langdon & McDonald in Salmo salar ().…”

“…Scale bar: a = 50 lm, b, c = 20 lm mentioned reservoirs. In a previous study on Paracheirodon axelrodi infected with E. pisciphila, we observed fungal hyphae in the gastrointestinal tract, which suggests that there were two possible routes of infection from an exogenous source: one was via the alimentary tract, where infective stages of the fungus pass across the intestinal mucosa and are subsequently disseminated to visceral organs, while the other route was via the accumulation of spores in the swim bladder via the pneumatic duct ( Rehulka et al, 2017).…”

“…The analysis of the ITS rDNA region (accession number LT604106) showed 99.8% (546/547 bp) similarity with the ex‐type strain of E. pisciphila CBS 537.73 (AF050272); the other species had 94% or lower similarity. We refer the readers to our recent study where a more detailed morphological description was published together with a summary of the host spectrum and phylogenetic placement of this species (Řehulka, Kolařík, & Hubka, ).…”

“…Preferentially, the kidney and the spleen of the stone moroko (Figure 6a,b) or the swim bladder of both fish species (Figure 6c) were invaded. Fijan (1969) was the first to describe E. pisciphila as the causative agent of severe systemic mycosis in channel catfish (Ictalurus punctatus); later, it was identified as a pathogen in at least four other fish species (reviewed by Rehulka et al, 2017). Contaminated food, water, decorative pieces of wood or stones in an aquarium may be exogenous sources of E. pisciphila.…”