Isolation, Identification and Characterization of a Novel Megalocytivirus from Cultured Tilapia (Oreochromis spp.) from Southern California, USA

In spring 2019, diseased four-month-old tilapia (Oreochromis spp.) from an aquaculture farm in Southern California, USA were received for diagnostic evaluation with signs of lethargy, anorexia, abnormal swimming, and low-level mortalities. At necropsy, non-specific external lesions were noted including fin erosion, cutaneous melanosis, gill pallor, and coelomic distension. Internal changes included ascites, hepatomegaly, renomegaly, splenomegaly, and multifocal yellow-white nodules in the spleen and kidney. Cultures of spleen and kidney produced bacterial colonies identified as Francisella orientalis. Homogenized samples of gill, brain, liver, spleen, and kidney inoculated onto Mozambique tilapia brain cells (OmB) developed cytopathic effects, characterized by rounding of cells and detaching from the monolayer 6–10 days post-inoculation at 25 °C. Transmission electron microscopy revealed 115.4 ± 5.8 nm icosahedral virions with dense central cores in the cytoplasm of OmB cells. A consensus PCR, targeting the DNA polymerase gene of large double-stranded DNA viruses, performed on cell culture supernatant yielded a sequence consistent with an iridovirus. Phylogenetic analyses based on the concatenated full length major capsid protein and DNA polymerase gene sequences supported the tilapia virus as a novel species within the genus Megalocytivirus, most closely related to scale drop disease virus and European chub iridovirus. An intracoelomic injection challenge in Nile tilapia (O. niloticus) fingerlings resulted in 39% mortality after 16 days. Histopathology revealed necrosis of head kidney and splenic hematopoietic tissues.

Fish from urban rivers and with high pollutant levels have shorter telomeres

Environmental pressures, such as urbanization and exposure to pollutants may jeopardize survival of free-living animals. Yet, much remains to be known about physiological and ecological responses to currently-released pollutants, especially in wild vertebrate ectotherms. We tested the effect of urbanization and pollution (phthalates, organochlorine and pyrethroid pesticides, polychlorobiphenyls, polybromodiphenylethers, polycyclic aromatic hydrocarbons, and some of their metabolites) on telomere length, a suggested biomarker of life expectancy, in the European chub, Squalius cephalus , from urban and agricultural rivers of the Marne hydrographic network, France. We showed that telomere length was reduced in chub from urban rivers. Moreover, among the wide range of anthropogenic contaminants investigated, high levels of phthalate metabolites in liver were associated with shorter telomeres. This study suggests that urbanization and chemical pollution may compromise survival of wild fish, by accelerating telomere attrition.

Acanthocephalan parasites collected from Austrian fishes: molecular barcoding and pathological observations

Acanthocephalan parasites were collected from the intestinal tracts of 137 predominantly wild fish (1 barbel Barbus barbus, 3 European chub Squalius cephalus, 13 rainbow trout Oncorhynchus mykiss and 120 brown trout Salmo trutta) from 12 localities. The condition factor, intensity of acanthocephalan infection and pathological lesions, if applicable, were documented. Routine bacteriology and virology were performed, and the brown trout were additionally tested for the presence of the myxozoan parasite Tetracapsolioides bryosalmonae by PCR. In total, 113 acanthocephalans were barcoded by sequencing a section of the mitochondrial cytochrome oxidase subunit I (COI) gene. Barcoding of the acanthocephalan tissues resulted in 77 sequences, of which 56 were assigned to Echinorhynchus truttae (3 genotypes), 11 to Pomphorhynchus tereticollis (9 genotypes), 9 to Acanthocephalus sp. (5 genotypes) and 1 to Neoechinorhynchida. Most of these genotypes were detected for the first time. Statistically, the acanthocephalan infection did not have an impact on the condition factor of the brown trout. Infection with P. tereticollis caused more severe pathological changes in the digestive tract than E. truttae. The present study provides new data regarding the distribution of acanthocephalan species in Austria and their impact on individual fish. In addition, new barcoding data from acanthocephalan parasites are presented, and the occurrence of P. tereticollis in European chub in Austria and in brown and rainbow trout in general was confirmed for the first time.

Detection of Squalius cephalus (Linnaeus, 1758), Carassius carassius (Linnaeus, 1758) and the khromist of Rutilus rutilus (Linnaeus, 1758) in the lower reaches of the Dnipro river in recent years

The article presents the materials on the detection of two very rare species of fish: the European chub Squalius cephalus (Linnaeus, 1758) and the crucian carp (the golden carp) Carassius carassius (Linnaeus, 1758) in the waters of the lower estuary of the Dnipro river in recent years. C. carassius is listed in the Red Book of Ukraine (2009). The article also describes the first encounter in these waters with the khromist of the common roach Rutilus rutilus (Linnaeus, 1758), which has a yellow-golden colour of the whole body. The basin of the Lower Dnipro includes the Kakhovske reservoir, the Ingulets river, several small tributaries and the lower unregulated part of the Dnipro riverbed along with the straits. Over the entire period of observation, up to 72 species of the round-mouthed fish and the fish from 59 genera and 19 families have been spotted in the fish fauna of the Lower Dnipro basin. According to some data, it is stated that within the migratory and freshwater species of the round-mouthed fish and the fish of the Lower Dnipro's ichthyocenosis only 21 out of 47 species of the native fish fauna have survived here. In general, the current fish fauna of the unregulated part of the Lower Dnipro amounts to 51 species of fish. The habitat of 28 species of fish in the lower estuary of the Dnipro river was confirmed in 2019.

Characterization of a Novel Megalocytivirus Isolated from European Chub (Squalius cephalus)

A novel virus from moribund European chub (Squalius cephalus) was isolated on epithelioma papulosum cyprini (EPC) cells. Transmission electron microscopic examination revealed abundant non-enveloped, hexagonal virus particles in the cytoplasm of infected EPC cells consistent with an iridovirus. Illumina MiSeq sequence data enabled the assembly and annotation of the full genome (128,216 bp encoding 108 open reading frames) of the suspected iridovirus. Maximum Likelihood phylogenetic analyses based on 25 iridovirus core genes supported the European chub iridovirus (ECIV) as being the sister species to the recently-discovered scale drop disease virus (SDDV), which together form the most basal megalocytivirus clade. Genetic analyses of the ECIV major capsid protein and ATPase genes revealed the greatest nucleotide identity to members of the genus Megalocytivirus including SDDV. These data support ECIV as a novel member within the genus Megalocytivirus. Experimental challenge studies are needed to fulfill River’s postulates and determine whether ECIV induces the pathognomonic microscopic lesions (i.e., megalocytes with basophilic cytoplasmic inclusions) observed in megalocytivirus infections.

Distribution of Heavy Metals (Ni, Co, Pb, Cd, Hg) in Tissues of European Chub (Squalius cephalus L.) from the Middle Course of the Nitra River, Slovakia

The aim of this study was to determine the levels of Ni, Co, Pb, Cd and Hg in the muscle, hepatopankreas, kidney and gonads of European chub (Squalius cephalus) from the middle course of the Nitra River, during spring and autumn seasons by AAS method. The concentrations of metals (mg.kg-1 wet weight) in the muscle ranged as follows: Ni 0.15-1.18, Co 0.09-0.58, Pb 0.39-1.66, Cd 0.04-0.29, Hg 0.85-2.71. Statistically significant differences among individual tissues, as well as between seasons have been recorded. Higher metals concentrations were detected in inner organs than in muscle. Permissible limits for safe consumption in the case of Pb, Cd and Hg have been exceeded in 100%, 95% and 100%, respectively. Currently, for the Co and Ni are not set any permissible limits.

Age Structure and Growth Dynamics of European Chub, Squalius cephalus, Linnaeus 1758 (Actinpterygii: Cyprinidae) from two Catchments in Transylvania-Romania

In recent years, research on water monitoring involves more and more the analysis of ichtyofauna in many aspects such as: the number of fish species, their distribution in the catchment sectors, the ratio between them, the dominant species, and growth dynamics and age structure of fish populations. The chub (Squalius cephalus), is in this case an indicator species. It is present in most rivers in Romania and it is well represented numerically. The specimens for our study were collected from the Someşul Mic River (Cluj County) respectively Târnava (Alba County). Growth dynamics in this case is a comparison tool, perfect for fish populations. Age category distribution from the catchments taken into study is also a tool that gives us important information. The absence of some age categories is a question mark related to environmental accidents that occurred on a river or river sector. Through this study, we intend to demonstrate that growth dynamics and age structure are effective tools for characterizing and comparing fish populations.