Henneguyosis: A novel threat to the exotic channel catfish Ictalurus punctatus cultivated in China

Abstract

Channel catfish Ictalurus punctatus is a freshwater fish of economic importance and has been worldwide introduced for aquaculture purposes. China has become the main producer of channel catfish and also the primary casualty of significant economic loss caused by various contagious diseases. Hence, surveillance of the causative agents can contribute to catfish industry security. In this study, the branchial infections that emerged in the domesticated channel catfish were reported in China, and three species of Henneguya were each determined to be responsible for the infection in single locality. Among these, the species isolated from Zhijiang City exhibited multifocal infection on the gills. It showed elongated lanceolate myxospores measured 14.8 ± 0.9 (12.6–16.7) × 3.9 ± 0.3 (3.4–4.7) × 3.5 ± 0.2 (2.9–3.9) μm and was distinct from the measurement of other congeners. A blast search against all sequences available in the Genbank database showed that H. exilis of 97.35% identity is the highest similarity to the present species. Accordingly, we denominated the Zhijiang isolates as Henneguya extensa n. sp. The second species were pooled from the surface of the gill filaments of catfish specimen sampled from Anqing City, showing myxospores measured 14 ± 1.3 (11.6–16.6) × 3.6 ± 0.2 (3.1–4) × 3.1 ± 0.2 (2.8–3.6) μm. It was identified as a species novel to the science based on the characteristic morphology and morphometrics. Therefore, we denominated it Henneguya anqingensis n. sp. A heavy burden of plasmodia formed by the third species that is destructive to the gill integrity was encountered in Yancheng City. By the identical morphology and overlapping morphometrics, this species was assigned to be Henneguya postexilisMinchew, 1977 initially reported from the USA. A pairwise sequence comparison and an evolution divergence analysis indicated a conspecific nature of the American and Chinese populations of H. postexilis. Phylogenetic analysis placed H. extensa n. sp. and H. postexilis in a clade comprising species predominantly infecting Ictaluridae fish native to North America. Histologically, the aggressive propagation of both H. extensa n. sp. and H. postexilis in the gills elicited extensive lamellar deformation and conspicuous occupation in the respiratory areas, potentially imposing survival pressure by suffocating the infected fish. Overall, the emergence of the branchial Henneguyosis was determined and, as the population of Henneguya species increased by the dense anthropogenic activity, may threaten the channel catfish industry in China.