The helminth parasites of freshwater fish have long proved an attractive field for parasitologists, and have spawned an extensive and voluminous literature. It was not until the seminal publications of Dogiel (1961, 1964), however, that attention was directed primarily to their ecology. Dogiel reviewed much of the existing literature in the light of ecological concepts, and examined the dependence of the parasite fauna as a whole, the parasitocoenosis, upon the environment. As well as laying down general principles, he discussed in detail (1961) the influence of physical factors, such as water chemistry and habitat size, and biological factors, such as host age, diet and migration, upon the composition of the parasite fauna of a host population. Dogiel’s reviews came to form the foundations not only for the study of the ecology of fish parasites, but also for the new discipline of ecological parasitology.

Helminth communities in freshwater fish: structured communities or stochastic assemblages?

Males and females can differ in levels of parasitism and such differences may be mediated by the costs of sexual selection or by ecological differences between the genders. In threespine stickleback, Gasterosteus aculeatus, males exhibit paternal care and territorial nest defence and the costs of reproduction may be particularly high for males relative to females. We monitored levels of parasitism for 15 years in a population of stickleback infected by four different parasite species. Consistent with general predictions, overall parasite prevalence (total parasitism) was greater in males than in females. However, this excess did not occur for each species of parasite. Males had higher prevalence of a cestode Cyathocephalus truncatus and a trematode Bunodera sp. relative to females, while females had higher prevalence of a cestode Schistocephalus solidus and nematodes. This suggested ecological sources to differences in parasitism rather than reproductive costs and therefore we examined diet of unparasitized stickleback, predicting that differences in dietary niche would influence relative parasitism. This was partially confirmed and showed that female stomach contents had increased frequency of pelagic items, the major habitat for the primary host of S. solidus whereas males exhibited increased frequency of benthic items, the dominant habitat of C. truncatus and Bunodera. Temporal shifts in the extent and direction of differential parasitism among years between the sexes were associated with temporal shifts in dietary differences. Our results, combined with those in the literature, suggest that ecological differences between genders could be a more important component to patterns of parasitic infection in natural populations than currently appreciated.

https://web.uvic.ca/%7Ereimlab/sdarticle.pdf

Ecological causes of sex-biased parasitism in threespine stickleback

Larvae (metacestodes) of tapeworms of the cyclophyllidean family Gryporhynchidae (previously included in the Dilepididae) occur in different internal organs of fresh- and brackish water fish (110 fish species of 27 families in 12 orders reported), which serve as the second intermediate hosts. The species composition, spectrum of fish hosts, sites of infection, and geographical distribution of gryporhynchids recorded from fish are reviewed here on the basis of literary data and examination of extensive material from helminthological collections. Metacestodes of the following genera have been found in fish: Amirthalingamia Bray, 1974 (1 species), Ascodilepis Guildal, 1960 (1), Cyclustera Fuhrmann, 1901 (4), Dendrouterina Fuhrmann, 1912 (1), Glossocercus Chandler, 1935 (3), Neogryporhynchus Baer et Bona, 1960 (1), Paradilepis Hsu, 1935 (5), Parvitaenia Burt, 1940 (2), and Valipora Linton, 1927 (3). However, most published records concern only three species, namely Neogryporhynchus cheilancristrotus (Wedl, 1855) from the intestinal lumen, Paradilepis scolecina (Rudolphi, 1819) from the liver and mesenteries, and Valipora campylancristrota (Wedl, 1855) from the gall bladder of cyprinids and other fish in the Palaearctic Region. Data on other species as well as reports from other regions are very scarce and almost no information is available from Australia, tropical Asia and South America. A recent study of gryporhynchid metacestodes from Mexico (Scholz and Salgado-Maldonado 2001), which reported 13 species, suggested that they may be more common than indicated by records in the literature. Although only a few cases of pathogenic influence of larvae on fish hosts have been reported, the veterinary importance of gryporhynchids remains to be assessed on the basis of more detailed studies. The data available indicate a strict host and site specificity of some species whereas others occur in a wide spectrum of fish hosts and are not strictly site-specific. Evaluation of Paradilepis larvae from the liver of salmonid fish from British Columbia, Canada, identified as P. simoni Rausch, 1949 by Ching (1982), has shown that they probably belong to two species, P. simoni and P. rugovaginosus Freeman, 1954. Metacestodes of the latter species and those of Cyclustera magna (Baer, 1959) from the intestinal wall of Tilapia zillii (Gervais) from Kenya are reported from fish for the first time.

/pdf/larvae-of-gryporhynchid-cestodes-cyclophyllidea-from-fish-a-1d2t9z5up9.pdf

Larvae of gryporhynchid cestodes (Cyclophyllidea) from fish: a review.

The parasitic fauna of two fish species, namely gill-netted samples of 652 Oreochromis leucostictus and 448 Tilapia zillii from Lake Naivasha and Oloidien Bay was investigated during the period from the end of October 1995 to September 1996. Five larval helminth parasites were recovered including the nematode, Contracaecum sp., the acanthocephalan Polyacanthorhynchus kenyensis, the digenetic trematode, Clinostomum sp. and two cestodes, Amirthalingamia sp. and Cyclustera sp. Both prevalence and intensity of the infection of these helminths increased in larger sized fish, whereas male fish were more heavily infected than females. No seasonality in infection level were observed. The health status of both fish species remained unaffected, although O. leucostictus from Oloidien Bay which harboured heavy infections of Contracaecum exhibited stuntedness and the lack of fatty deposits around the digestive caecum.

https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S0022149X0200015X

A comparative study of helminth parasites from the fish Tilapia zillii and Oreochromis leucostictus in Lake Naivasha and Oloidien Bay, Kenya

Summary
Total African aquaculture production in 1994 amounted to 76 660 metric tonnes (t). Of this, 53.8% (41 211 t) was produced by five countries bordering the Mediterranean, while the remainder (35 449 t or 46.2%) was produced by 30 sub-Saharan countries. These figures highlight the low-level intensity of aquaculture in sub-Saharan Africa. A comprehensive literature search was undertaken to gauge the extent of disease and pathogenic agents in fish and shellfish aquaculture in Africa south of the Sahara. The study revealed that bacterial infections as well as parasitic ectoprotozoans, cestodes, trematodes, nematodes, polychaetes and crustaceans are the most prevalent problems in African freshwater, brackish water and marine aquaculture. There have been isolated reports of viral diseases (infectious pancreatic necrosis (IPN), lymphocystis and spring viraema). Bacterial diseases are restricted to common agents such as Aeromonas, myxobacteria and some other ubiquitous facultative bacteria. Saprolegnia is the most common problematic fungus affecting fish under culture conditions. Currently the most widely used chemicals for prophylaxis and treatment include wide spectrum antibiotic formulations, malachite green, methylene blue, formalin, copper sulphate, salt, and several organ-ophosphates. From an aquaculture perspective it was noteworthy that disease and parasite infestation have been poorly studied in Africa as a whole and in sub-Saharan Africa in particular (South Africa being the exception). It is hypothesized that this is mainly due to the low-level intensity of aquaculture in the region. At present the paucity of research on fish diseases in Africa is not seen as a factor that will negatively impact on aquaculture development and as such is not a target research area. Africa is considered to be the sleeping giant of aquaculture and at the present moment it is relatively disease free. It is vitally important that African countries take steps to safeguard this status. One method of accomplishing this is to restrict the importation of fishes into Africa. The importation of ornamental aquarium fish as well as hybrid and genetically improved fish strains pose the greatest threats. The smorgasbord of fish and shellfish parasites and diseases that occur in Israel, for example, can to a large extent be ascribed to uncontrolled translocations. Every effort needs to be made to prevent a similar occurrence in Africa.

Vijaya Batra

Papers

Prevalence of helminth parasites in three species of cichlids from a man‐made lake in Zambia