RESUMEN

A new species of philometrid nematode, Philometroides africanus sp. n., is described from female specimens found encapsulated in gill arches and inner surface of gill covers of the African pike, Hepsetus odoe (Bloch), an endemic freshwater fish in Africa, from the Okavango River and Delta in Botswana. This new nematode is characterised mainly by a markedly small and plump body of gravid females (body length 6-9 mm), a separate anterior oesophageal bulb, a conspicuously small oesophageal gland, presence of four pairs of very small submedian cephalic papillae, and absence of any caudal processes. The prevalence of P. africanus in African pike of the Okavango Delta was 29%, with the intensity 1-8 (mean 3) encapsulated nematodes per fish. The genus Margolisianum Blaylock et Overstreet, 1999 is considered a junior synonym of Philometroides Yamaguti, 1935 and, consequently, its type species is transferred to the latter as Philometroides bulbosus (Blaylock et Overstreet, 1999) comb. n.

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RESUMEN

During surveys of the fish parasites of Lake St Lucia on the coast of northern KwaZulu-Natal, specimens of an hitherto undescribed argulid were found on the skin of the kelee shad Hilsa kelee (Cuvier). This, only the fourth argulid species to be found in South African coastal waters, is here described as Argulus izintwala n. sp.

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A new species, Gnathia nkulu sp. n. is described from material collected off the South African coast at 80-200m depth. It differs from the intertidal species Gnathia africana Barnard, 1914 in that the mediofrontal process is not deeply divided into two lobes, article 2 of the pylopod is rounded and small wart-like tubercles and long simple setae are present on both the cephalosome and pereon.

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A redescription of the adult male of Caecognathia cryptopais (Barnard, 1925) is provided from syntypes and other material deposited in the South African Museum. The generic status of Caecognathia cryptopais is also revised. This redescription is based on light and scanning electron microscopy.

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Specimens of the freshwater snail Bulinus tropicus (Krauss, 1848) collected in the Free State, South Africa shed cercariae with an oral collar bearing 27 spines. Tadpoles of the African clawed toad Xenopus laevis laevis Daudin, 1802 collected from the same waters harbored metacercariae with a similar collar of spines. Adults were obtained after feeding infected tadpoles to laboratory-reared reed cormorants, Phalacrocorax africanus (Gmelin, 1789). The parasite was identified as Petasiger variospinosus (Odhner, 1910), the life cycle was experimentally completed, and stages described by the use of light and scanning electron microscopy.

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Argulus kosus Avenant-Oldewage, 1994 was described from two females collected in Kosi Bay, South Africa. Individuals of both sexes have now been found associated with freshwater, estuarine and marine fishes in Lake St Lucia on the coast of northern KwaZulu/Natal. The male is described, and A. smalei Avenant-Oldewage & Oldewage, 1995 is synonymised with A. kosus.

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The strigeoid metacercaria Diplostomulum xenopi is commonly found in the pericardial cavity of Xenopus laevis laevis. This paper provides the first description of the adult obtained from the intestine of an experimental host, the darter, Anhinga melanogaster. Natural cercarial infections were found in specimens of the freshwater snail Bulinus tropicus collected from dams in the Free State. South Africa. The life cycle was experimentally completed and all stages were described by light and scanning electron microscopy.

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A population of a trichodinid (Ciliophora: Peritrichia) was found in the gut of the surgeonfish Acanthurus xanthopterus collected from Hawaii, South Africa and New Guinea and described as a new species. This is only the second record of a trichodinid from the intestine of a marine fish. In all the fish specimens examined, the micro-fauna normally found in other species of the fish family. Acanthuridae was absent and replaced entirely by the trichodinid population.

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Reconstructions from serial sections reveal that the digestive system consists of a pharynx esophagus, crop, midgut, and rectum. Two main stems from the branched enteral diverticula are connected to the lateral regions of the crop by right rind left arms. Glandular tissue surrounds the enteral diverticula proximally. A strong sphincter separates the crop and midgut, whereas the midgut and rectum are separated by a weak sphincter. Cuboidal epithelium lines the pharynx, esophagus, crop, and rectum, whereas cuboidal and club-shaped epithelia line the midgut. The cuboidal cells possess elongated nuclei and numerous vacuoles, suggesting that absorption takes place in the midgut.

RESUMEN

Because of the antithrombotic and anti-inflammatory properties of the n-3 fatty acids, eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), which are found in large quantities in marine fish, the fatty acid composition of the flesh of 18 different species of fresh-water fish found in South Africa was analysed by capillary gas chromatography. In general all the fish studied had low percentages of EPA and DHA and fairly high percentages of arachidonic acid and linoleic acid when compared with some marine fish. The saturated fats constituted 33% of total fatty acids and the mono-enes averaged 35%. The fish studied are therefore not as good a source of n-3 fatty acids as marine fish.

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Ciliophorons of the family Trichodinidoe comprise seven genera, all of which are commensolists or parasites - mainly on aquatic hosts such as other ciliophorans, coelenterates, planctonic crustaceans, molluscs, echinoderms, amphibians and fish. Although the first species of this family, Trichodina pediculus, was described from material collected from Hydra, most literature concerns the trichodinids of fish-particularly cultured freshwater fish. These ciliophorans have been implicated in severe disease and mortalities of fish, causing severe economic losses in various parts o f the world. In spite o f the confused taxonomy o f the Trichodinidae, it now appears that they fall into four distinct groups representing a line of specialization towards a more exclusive niche on the host fish. The more opportunistic species, with a broad host range, tend to be larger skin parasites, while the more specialized are smaller and usually only parasitize the gills o f their specific host.