Endoparasites of fresh water fishes from rivers in Edo State, Nigeria

Parasites of fish constitute one of the major problems to fish health. Parasites of fish have been a great concern since they often cause disease conditions in fishes. This study described the parasitic faunas of eight fresh water bodies in Edo state (Ikpoba river, Ogba river, Ujogba river, Niger river at Illushi, Obe river, Gelegele river, Niger river at Agenebode and Osomegbe river). The duration of fish sampling was from October, 2017 to November, 2017.The fish samples (whole catch sourced from fishermen) were collected for identification, morphometric analysis and examination for the presence of parasites. One-way ANOVA and Tukey Honest Test were used to compare the data among size classes at the level of p <0.05. Three orders (Lepidosirenformes, Siluriformes and Polyteriformes), eight families (Protopteridae, Clariddidae, Channiddae, Polypterididae, Melapteridae, Clarotidae, Cichlidae and Lorcariidae) and fourteen genera were examined. The study had an overall prevalence of 25.34%. The highest prevalence of fish parasitic infection was recorded in Niger river along Agenebode. Overall, parasite taxa recovered were nematodes (65.50%), trematodes (27.00%), cestodes (4.27%) and acanthcephalans (3.27%). The most infected fish species was Clarias gariepenus (13.77%). The helminth taxa (nematodes) had the highest prevalence of parasites (65.50%). The largest number of parasites isolated was Camallanus cotti (30.43%) and Procamallanus laevionchus (17.39%). This study showed river Niger at Agenebode with most parasitic prevalence, nematodes as the most prevalent parasitic taxa and Clarias gariepenus as the most infected fish species. Keywords: Edo state, Freshwater fishes, Fish parasites, Helminths, Parasite taxa, Nigeria

Novel parasite invasion leads to rapid demographic compensation and recovery in an experimental population of guppies

The global movement of pathogens is altering populations and communities through a variety of direct and indirect ecological pathways. The direct effect of a pathogen on a host is reduced survival, which can lead to decreased population densities. However, theory also suggests that increased mortality can lead to no change or even increases in the density of the host. This paradoxical result can occur in a regulated population when the pathogen’s negative effect on survival is countered by increased reproduction at the lower density. Here, we analyze data from a long-term capture–mark–recapture experiment of Trinidadian guppies (Poecilia reticulata) that were recently infected with a nematode parasite (Camallanus cotti). By comparing the newly infected population with a control population that was not infected, we show that decreases in the density of the infected guppy population were transient. The guppy population compensated for the decreased survival by a density-dependent increase in recruitment of new individuals into the population, without any change in the underlying recruitment function. Increased recruitment was related to an increase in the somatic growth of uninfected fish. Twenty months into the new invasion, the population had fully recovered to preinvasion densities even though the prevalence of infection of fish in the population remained high (72%). These results show that density-mediated indirect effects of novel parasites can be positive, not negative, which makes it difficult to extrapolate to how pathogens will affect species interactions in communities. We discuss possible hypotheses for the rapid recovery.

Mutual dilution of infection by an introduced parasite in native and invasive stream fishes across Hawaii

SUMMARYThe presence of introduced hosts can increase or decrease infections of co-introduced parasites in native species of conservation concern. In this study, we compared parasite abundance, intensity, and prevalence between nativeAwaous stamineusand introduced poeciliid fishes by a co-introduced nematode parasite (Camallanus cotti) in 42 watersheds across the Hawaiian Islands. We found that parasite abundance, intensity and prevalence were greater in native than introduced hosts. Parasite abundance, intensity and prevalence withinA. stamineusvaried between years, which largely reflected a transient spike in infection in three remote watersheds on Molokai. At each site we measured host factors (length, density of native host, density of introduced host) and environmental factors (per cent agricultural and urban land use, water chemistry, watershed area and precipitation) hypothesized to influenceC. cottiabundance, intensity and prevalence. Factors associated with parasitism differed between native and introduced hosts. Notably, parasitism of native hosts was higher in streams with lower water quality, whereas parasitism of introduced hosts was lower in streams with lower water quality. We also found that parasite burdens were lower in both native and introduced hosts when coincident. Evidence of a mutual dilution effect indicates that introduced hosts can ameliorate parasitism of native fishes by co-introduced parasites, which raises questions about the value of remediation actions, such as the removal of introduced hosts, in stemming the rise of infectious disease in species of conservation concern.

Rhabdochona (Rhabdochona) keralaensis sp. nov. (Rhabdochonidae) and some other nematodes in the Indian mottled eel Anguilla bengalensis bengalensis from India

A new species of parasitic nematode, Rhabdochona (Rhabdochona) keralaensis sp. nov., is described based on specimens recovered from the intestine of Anguilla bengalensis bengalensis (Gray) collected from the freshwater bodies of Kerala State, southern India. It is characterized mainly by the presence of ten anterior prostomal teeth, absence of basal teeth, simple deirids, length of spicules, number and arrangement of preanal papillae and non-filamented eggs. Two species of camallanid nematodes, adults of Camallanus cotti Fujita, 1927 and a single Procamallanus (Spirocamallanus) sp. fourth-stage larva, were also recorded from A. bengalensis. Camallanus cotti, a pathogenic parasite of many species of wild and aquarium-reared fishes in many countries of South and East Asia, Europe, South and North America, West Indies and Australia, is reported for the first time from a representative of the fish family Anguillidae. Descriptions of R. (R.) keralaensis and Indian specimens of C. cotti, based on light and scanning electron microscopical examinations, are provided. Camallanus oxygasterae Gupta et Bakshi, 1983 is considered a junior synonym of C. cotti.