Asaccotrema vietnamiense n. gen.; n. sp. (Trematoda: Monorchioidea), a new aberrant representative of lissorchiid trematodes from the sidestripe rasbora, Rasbora paviana Tirant (Actinopterygii: Cyprinidae), Vietnam

Sokolov, Sergey G., Gordeev, Ilya I. (2019): Asaccotrema vietnamiense n. gen.; n. sp. (Trematoda: Monorchioidea), a new aberrant representative of lissorchiid trematodes from the sidestripe rasbora, Rasbora paviana Tirant (Actinopterygii: Cyprinidae), Vietnam. Zootaxa 4674 (4): 451-462, DOI: 10.11646/zootaxa.4674.4.

Parasites of the Antarctic toothfish (Dissostichus mawsoni Norman, 1937) (Perciformes, Nototheniidae) in the Pacific sector of the Antarctic

The Antarctic toothfish (Dissostichus mawsoni Norman, 1937) is one of the main target species of commercial fisheries in the Antarctic. It is an endemic and is found along the shelf of Antarctica, as well as on the slopes of seamounts, underwater elevations and islands in the sub-Antarctic. It feeds on a variety of fish and cephalopods and can be an intermediate/paratenic host of some helminthes, whose final hosts are whales, seals, large rays and sharks. This article presents new data on toothfish infection in the Pacific sector of the Antarctic. Specimens were examined during commercial longline fishing in the Ross Sea and the Amundsen Sea in January–February 2013. Fourteen species of parasites were found using standard parasitological methods and genetic analysis.Keywords:  Toothfish; parasites; Antarctic fisheries; CCAMLR; infection; Southern Ocean.(Published: 24 June 2016)Citation: Polar Research 2016, 35, 29364, http://dx.doi.org/10.3402/polar.v35.2936

Abnormal gonads in the Antarctic toothfish (Dissostichus mawsoni Norman, 1937 [Perciformes: Nototheniidae]): the first record and histological description

This paper describes the morphology and histology of abnormal gonads in Antarctic toothfish (Dissostichus mawsoni) and the possibility of intersexuality and senescence of some individuals. Two old (approximately 25 years) and large (184–185 cm) specimens with abnormal gonads were caught in the Antarctic during commercial fishing for toothfish and studied using histological methods. Although D. mawsoni is well-known and extensively studied, this is the first study dealing with abnormal gonads in the species. The histological analysis revealed that the gonads of the first specimen contained both male and female germ cells (ovotestis), the testicular and ovarian tissues being separated by a thick layer of connective tissue. The female portion was composed of secondary vitellogenic oocytes, primary vitellogenic, cortical alveolar and primary growth oocytes, while the testes contained cysts of spermatogonia and primary spermatocyte. The gonads of the second specimen were small, filiform and showed massive growth of the connective tissue, which occupied almost the entire gonad; a few spermatogonia without visible cysts were found. This study extends our understanding of sexual development in Antarctic toothfish, documenting the possibility of long-term interruptions in the reproductive cycle of this species

Phylogenetic Evidence for the Lissorchiid Concept of the Genus Anarhichotrema Shimazu, 1973 (Trematoda, Digenea)

Anarhichotrema Shimazu, 1973 is a monotypic digenean genus, with the type- and only species, Anarhichotrema ochotense Shimazu, 1973, known to infect North Pacific fishes. This genus was originally described as a member of the Lissorchiidae (Monorchioidea) and later moved to the Zoogonidae (Microphalloidea). Its exact phylogenetic position has remained unresolved due to the lack of molecular data. In this study, we isolated specimens of A. ochotense from the Bering wolffish, Anarhichas orientalis Pallas, 1814 caught in the Sea of Okhotsk, described them morphologically and performed a molecular phylogenetic analysis of their nuclear 18S and 28S rDNA regions. The specimens examined in our study generally corresponded to previous morphological descriptions of A. ochotense but were noticeably smaller, possibly due to the crowding effect. The phylogenetic analysis placed Anarhichotrema within the Lissorchiidae as a sister taxon to the group comprising freshwater lissorchiids. Thus, we restore Anarhichotrema to the Lissorchiidae, as originally assigned

Phylogenetic Evidence for the Lissorchiid Concept of the Genus <i>Anarhichotrema</i> Shimazu, 1973 (Trematoda, Digenea)

Anarhichotrema Shimazu, 1973 is a monotypic digenean genus, with the type- and only species, Anarhichotrema ochotense Shimazu, 1973, known to infect North Pacific fishes. This genus was originally described as a member of the Lissorchiidae (Monorchioidea) and later moved to the Zoogonidae (Microphalloidea). Its exact phylogenetic position has remained unresolved due to the lack of molecular data. In this study, we isolated specimens of A. ochotense from the Bering wolffish, Anarhichas orientalis Pallas, 1814 caught in the Sea of Okhotsk, described them morphologically and performed a molecular phylogenetic analysis of their nuclear 18S and 28S rDNA regions. The specimens examined in our study generally corresponded to previous morphological descriptions of A. ochotense but were noticeably smaller, possibly due to the crowding effect. The phylogenetic analysis placed Anarhichotrema within the Lissorchiidae as a sister taxon to the group comprising freshwater lissorchiids. Thus, we restore Anarhichotrema to the Lissorchiidae, as originally assigned

Abnormal gonads in the Antarctic toothfish (Dissostichus mawsoni Norman, 1937 [Perciformes: Nototheniidae]): the first record and histological description

This paper describes the morphology and histology of abnormal gonads in Antarctic toothfish (Dissostichus mawsoni) and the possibility of intersexuality and senescence of some individuals. Two old (approximately 25 years) and large (184–185 cm) specimenswith abnormal gonadswere caught in the Antarctic during commercial fishing for toothfish and studied using histological methods. Although D. mawsoni is well-known and extensively studied, this is the first study dealing with abnormal gonads in the species. The histological analysis revealed that the gonads of the first specimen contained both male and female germ cells (ovotestis), the testicular and ovarian tissues being separated by a thick layer of connective tissue. The female portion was composed of secondary vitellogenic oocytes, primary vitellogenic, cortical alveolar and primary growth oocytes, while the testes contained cysts of spermatogonia and primary spermatocyte. The gonads of the second specimen were small, filiform and showed massive growth of the connective tissue, which occupied almost the entire gonad; a few spermatogonia without visible cystswere found. This study extends our understanding of sexual development in Antarctic toothfish, documenting the possibility of long-term interruptions in the reproductive cycle of this species

Composition of leucocytes in peripheral blood of Patagonian toothfish (Dissostichus eleginoides, Smitt, 1898) (Nototheniidae)

The composition of leukocytes in the Patagonian toothfish (Dissostichus eleginoides Smitt, 1898), caught in the Scotia Sea at a depth of more than 1000 m, was studied. Cells with various morphofunctional characteristics and cell structure were found. Lymphocytes were predominant, followed by, in decreasing order, eosinophils, monocytes, blast forms and neutrophils. The composition of leukocytes in the Patagonian toothfish consists of the same types of leukocytes as the earlier studied Antarctic toothfish (Dissostichus mawsoni Norman, 1937), but the percentage of white blood cells in the leukocyte formula differs between the two species

Composition of leucocytes in peripheral blood of Patagonian toothfish (Dissostichus eleginoides, Smitt, 1898) (Nototheniidae)

The composition of leukocytes in the Patagonian toothfish (Dissostichus eleginoides Smitt, 1898), caught in the Scotia Sea at a depth of more than 1000 m, was studied. Cells with various morphofunctional characteristics and cell structure were found. Lymphocytes were predominant, followed by, in decreasing order, eosinophils, monocytes, blast forms and neutrophils. The composition of leukocytes in the Patagonian toothfish consists of the same types of leukocytes as the earlier studied Antarctic toothfish (Dissostichus mawsoni Norman, 1937), but the percentage of white blood cells in the leukocyte formula differs between the two species

A Phylogenetic Re-Evaluation of the Stenakrine Opecoelids (Trematoda, Digenea: Opecoeloidea) with Some Taxonomic Novelties

The Opecoeloidea is a large group of xiphidiate digeneans parasitizing marine and freshwater fishes. According to the current taxonomic model, this superfamily contains only one family with numerous subfamilies. This study is devoted to the members of the Stenakrinae. Based on phylogenetic analysis of concatenated sequences of 18S and 28S rRNA genes of stenakrine opecoelids Caudotestis dobrovolski, C. cf. dobrovolski, Hexagrammia zhukovi, Stenakron vetustum, as well as the deep-sea xiphidiate digenean Zdzitowieckitrema incognitum, which so far has had an ambiguous phylogenetic status, we erect a new opecoeloid family, the Zdzitowieckitrematidae fam. nov. The genera Holsworthotrema and Scorpidotrema are removed from the Stenakrinae to the Scorpidotrematinae subfam. nov. within the Opecoelidae. We also remove the Stenakrinae from the Opecoelidae and recognize it as a separate family within the Opecoeloidea. The Stenakridae stat. nov. is a sister taxon to a well-supported Opecoelidae. The Zdzitowieckitrematidae occupies a sister position relative to the stenakrids and the opecoelids taken together. All three families are clearly phylogenetically distinct, however convincing morphological differences are revealed only between the Zdzitowieckitrematidae and the Stenakridae and between the Opecoelidae and the Stenakridae