Histopathology of Kabatana arthuri (Microspora) infection in sutchi catfish, Panagasius sutchi

Parasitic fauna of farmed freshwater ornamental sutchi catfish (Pangasiandon hypophthalmus) and silver dollar (Metynnis hypsauchen) in Alborz province, Iran

BACKGROUND

Parasitic infestations are one of the most significant problems in global aquaculture. In addition to direct economic losses due to significant mortalities, parasites may have a significant negative impact on the fish's behaviour, energetic demands, trophic position, interspecific competition, growth rate, and reproductive function.

OBJECTIVES

We conducted the present study to evaluate the infection status of parasitic pathogens in freshwater sutchi catfish (Pangasianodon hypophthalmus) and silver dollar (Metynnis hypsauchen) farmed in Alborz province of Iran.

METHODS

Between January and February 2021, 140 ornamental fish, including 70 sutchi catfish (P. hypophthalmus) and 70 silver dollar (M. hypsauchen), were delivered from various ornamental fish farms for parasitological analysis. Thorough macroscopic and microscopic examinations were performed to detect parasitic infections in delivered freshwater ornamental fish.

RESULTS

A total of six parasite species, including five protozoan species (Nyctotherus piscicola, Trichodina heterodentata, Ichthyophthirius multifiliis, Protoopalina sp., and Hexamita sp.) and one monogenean species (Ancyrocephalus sp.), were identified in the examined fish. The overall prevalence of the recovered parasites was 46.43% (65/140) of the fish.

CONCLUSIONS

In the current study, several parasites, including Hexamita sp., Ancyrocephalus sp., Protoopalina sp., and N. piscicola, were identified as the first records of the sutchi catfish (P. hypophthalmus) and/or silver dollar (M. hypsauchen), and these two fish species are known as new hosts for the isolated parasites in ornamental fish farms in Iran. Assessing the parasitic fauna of ornamental fish is therefore critical for preventing parasite introduction into adjacent provinces as well as neighbouring countries and promoting fish health.

Ultrastructural and molecular characterization of a new microsporidium parasite from the Amazonian fish, Gymnorhamphichthys rondoni (Rhamphichthyidae)

A new species of a microsporidium found in the freshwater teleost Gymnorhamphichthys rondoni, collected on the lower Amazon River, is described based on light, ultrastructural, and phylogenetic studies. This parasite develops in the skeletal muscle of the abdominal cavity, forming whitish cyst-like structures containing numerous spores. Mature spores, lightly pyriform to ellipsoidal with rounded ends and measuring 4.25 ± 0.38 × 2.37 ± 0.42 µm (n  =  30), were observed. The spore wall, which measured about 102 nm, was composed of 2 layers with approximately the same thickness. The isofilar polar filament was coiled, with 9-10 (rarely 8) turns. The posterior vacuole appeared as a pale area, occupying about 1/3 of the spore length, and contained a spherical posterosome composed of granular material that was denser at the periphery. The myofibrils located near the spores appeared to be in advanced degradation. Molecular analysis of the rRNA genes, including the ITS region, and phylogenetic analyses using maximum parsimony, maximum likelihood, and Baysesian inference were performed. The ultrastructural characteristics of the spores and the phylogenetic data strongly suggested that it is a new species related to Kabatana, Microgemma, Potaspora, Spraguea, and Tetramicra. We named this new microsporidian from Amazonian fauna as Kabatana rondoni n. sp.

A NEW MICROSPORIDIAN INFECTING THE MUSCULATURE OF THE ENDANGERED TIDEWATER GOBY (GOBIIDAE)

A previously unrecognized microsporidian (Kabatana newberryi n. sp.) is described from the musculature of Eucyclogobius newberryi (Gobiidae) in Big Lagoon, Humboldt County, California. Spores are ovoid, ranging in size from 2.8 +/- 0.3 microm in total length and 1.9 +/- 0.4 microm in width (measurements of 30 spores made by calculation from micrograph). The polar filament has 9-10 coils in 1-2 rows. Development occurs in direct contact with host muscle cell cytoplasm, without xenoma or sporophorous vesicle. Phylogenetic analysis of the new species and of 35 other microsporidians known to infect fish using 1115 base pairs of aligned 16S rRNA gene indicate the new species is most closely related to Kabatana takedai. However, the new species differs by 11% sequence divergence from K. takedai. Divergence in morphology and genetic data allow for diagnosis from all other fish-infecting microsporidia and supports recognition of a new species of microsporidian, Kabatana newberryi n. sp., presently known only from a suspected specific host, the endangered tidewater goby Eucyclogobius newberryi.

Occurrence of a new microsporidium in the skeletal muscle of the flying fish Cypselurus pinnatibarbatus japonicus (Exocoetidae) from Yakushima, Japan

A new microsporidium was observed in the flying fish Cypselurus pinnatibarbatus japonicus (Franz) (Exocoetidae) from Yakushima, Japan. Visual examination revealed the microsporidium to form white elongate nodules in the host's trunk muscle. Monomorphic spores were ovoid to pyriform in shape, with average dimensions of 4.1 x 2.2 microm and possessing a polar tube describing 13-15 coils. Histological observations showed that each parasite focus of infection was encapsulated by a host-produced fibrous membrane. The presence of sporophorous vesicles was not clearly determined. Ribosomal DNA sequence analyses showed the microsporidium to be discrete from other known fish muscle-infecting species and to be most closely related to a clade comprising the Pleistophoridae and Glugea spp. The parasite is provisionally placed as Microsporidium cypselurus sp. n.