Studies on ascaridid, oxyurid and enoplid nematodes (Nematoda) from fishes of the Okavango River, Botswana

Abstract

Based on light and scanning electron microscopical studies, eight species (five adult and three larval) of nematodes belonging to the Ascaridida, Oxyurida and Enoplida were collected from fishes of the Okavango River, Botswana, namely Falcaustra similis Moravec et Van As, 2004, Atractidae gen. sp. (only female) (both Cosmocercoidea), Cucullanus sp. (only female) (Seuratoidea), Cithariniella longicaudata sp. n., Synodontisia annulata sp. n. (both Oxyuroidea), Contracaecum sp. third-stage larvae, third-stage larvae of Galeiceps sp. (both Ascaridoidea) and Eustrongylides sp. fourth-stage larvae (Dioctophymatoidea). The new species Citharinella longicaudata (type host Schilbe intermedius Rüppel) is mainly characterised by the shape and size of cephalic papillae and the spicule 108 µm long, and Synodontisia annulata (type host S. intermedius) by the shape of cephalic papillae, body length of gravid females (4.88-5.33 mm) and a short spicule (66 µm long). The female specimen of Cucullanus sp. from Tilapia sparmanni Smith markedly differs from congeners parasitising inland fishes in Africa by the elongate pseudobuccal capsule and by the excretory pore far posterior to the oesophago-intestinal junction; apparently, it belongs to an undescribed species. Galeiceps larvae parasitising fishes are described for the first time. This paper is a continuation of these studies, based on the same nematode collection, now providing results of the systematic evaluation of nematodes of the orders Ascaridida, Oxyurida and Enoplida. Detailed morphological examinations (using both light and scanning electron microscopy) of these materials revealed the presence of several species, including three new taxa of adults and previously undescribed larvae of a little-known anisakid genus. The results are presented herein. MATERIALS AND METHODSA total of 169 specimens belonging to nine fish species of the families Alestidae, Cichlidae, Clariidae, Mochokidae and Schilbeidae were collected in the Okavango River (mainstream in the Shakawe area) in the Panhandle, by gill nets, cast-nets and electro-fishing. Fish were taken live to a nearby field laboratory and maintained unfed in plastic tanks for at least two days to allow the gut to empty. The fish were anaesthetised and killed using MS222 and the internal organs were removed and placed in 1% saline. Nematodes removed from the digestive tract and viscera were fixed in 4% or 10% buffered neutral formalin.For light microscopical examination, the nematodes were cleared gradually in glycerine. Drawings were made with the aid of a Zeiss microscope drawing attachment. Specimens used for scanning electron microscopy (SEM) were post-fixed in 1% osmium tetroxide (in phosphate buffer), dehydrated through a graded ethanol series, critical-point-dried and sputter-coated with gold; they were examined using a JEOL JSM-7401F scanning electron microscope at an accelerating voltage of 4 kV (GB low mode). All measurements are in micrometres unless otherwise indicated. Only small numbers of the available s...

Some nematodes, including two new species, from freshwater fishes in the Sudan and Ethiopia

“…The morphology of available specimens is identical with that reported by Moravec and Van As (2015a). Third-and fourth stage larvae of Eustrongylides Jägerskiöld, 1909 from fishes and some other aquatic vertebrates, serving as paratenic hosts, are unidentifiable to species by morphological and biometrical features.…”

“…Koubková et al 2008, Moravec et al 2009a,b, 2013, Moravec and Jirků 2014a,b, 2015, Moravec and Van As 2015a,b,c,d, González-Solís and Mariaux 2017. Erection of so many new nematode taxa within such a short period documents again that the composition of the fauna of African fish nematodes remains to be little known.…”

“…in Africa. With respect to the paper of Moravec and Van As (2015a), all previous records of C. citharini Khalil, 1964 from Synodontis spp. in Egypt concerned in fact C. khalili.…”

“…Since the interspecific differences of Cithariniella spp. are mainly found in males (Koubková et al 2010, Moravec andVan As 2015a), the identification of the present specimens is principally based on the genus of the definitive host. According to Moravec and Van As (2015a), C. khalili is the only species of this genus parasitising Synodontis spp.…”

Some nematodes from freshwater fishes in central Africa

“…The general morphology of this female larva, especially the presence of a distinct sclerotised apparatus inside the bulbous posterior portion of the oesophagus, indicates that it belongs to the Atractidae. Recently Moravec and Van As (2015a) reported a nongravid female designated as Atractidae gen. sp. from the intestine of the catfish Schilbe intermedius Rüppel (Schilbeidae) in Bot- swana, which, however, differs from the present specimen in a larger body, a distinct pharyngeal portion of the oesophagus and isthmus and in the location of the vulva in the anterior part of the body.…”