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Indigenous South African Labeo spp. show promise with regard to development of semi-intensive aquaculture, yet little research on their monogenean fauna has been conducted. Ecological aspects of monogenean fauna of the moggel Labeo umbratus (Smith 1841) and the Orange River mudfish Labeo capensis (Smith 1841), as recorded during both winter and summer sampling surveys, are reported here. Fish were collected using gill nets, euthanized and gills removed and examined to both quantify parasite numbers and distribution on the gills. Results obtained support the hypothesis that gill site preference is not due to active choice for a particular attachment site, but rather a result of water flow over gills during respiration in conjunction with fish behaviour and habitat use. Interaction between individual elements investigated (temperature effects, parasite population dynamics and host population dynamics) may be largely responsible for seasonal differences in infection statistics of monogenean parasites. Such interactions should be investigated in future large scale ecological studies, in combination with experimental studies, to further elucidate these effects.
The studies were carried out during the period April 1982 - July 1984. The statistical analysis of the dependence between the temperature and the intensity of occurrence of 4 species of the genus Dactylogyrus in bream (Abramis brama L.) was made in two variants (tab. 1, 2). In both cascs correlation coefficients between the variables, as well as regression coefficients, estimating the linear dependence according to the equation: y = a±bx (cf. fig. 1a-d). The correlation coefficient was verified using the t Student test. The statistical analysis has not revealed any statistically significant dependence between mean month temperatures during the whole investigation period, and the intensity of occurrence of particular of the genus Dactylogyrus species. However, a highly significant (+ +) and significant (+) correlation has been found between the temperature differences in consecutive months of investigations, and the intensity of occurrence of particular species. This confirms the previous suggestion that the studied species of the genus Dactylogyrus react to the temperature changes in the environment. In agreement with calculated coefficients, the higher the temperature difference within a short period, the greater the changes of the density in the population. The density of all the species was the highest in March when the temperature increased by ca. 4°C within a month, and the lowest in October or November at the temperature decrease by ca. 4.5°C. It can be assumed that a rapid temperature increase enhances the reproductive activity of the parasites and their expansion to the hosts, white a rapid decrease inhibits their reproduction and possibly increases also the mortality of adult individuals.
Four new Dactylogyrus spp. are described from twо cyprinid fishes of the Bahu-Kalat River (Southeast in): D. faridpaki sp. n. and D. eslamii sp. n. infected the gills of Crossocheilus latius, while D. yousefpouri sp. n. and D. mobedii were found on Aspidoparia morar. The morphological peculiarities of monogeneans of these endemic fishes and their relation to the Indian Great Fauna Region are discussed.
A study was made on the Monogenea of 417 Cyprinus carpio. Carp were captured monthly between May 1990 and September 1991 in the central basin of the Llobregat river in the NE of Spain. Gyrodactylus cyprini, G. katharineri, Dactylogyrus anchoratus, D. extensus and Dactylogyrus minutus were identified on these fish. Gyrodactylus cyprini, G. katharineri and D. minutus are recorded in Spain for the first time. Gyrodactylus spp. have always been found on the fins and skin and Dactylogyrus spp. were found on the gills. Gyrodactylus spp. infected 19.42% of the hosts and Dactylogyrus spp. infected 72.42% of the fish. All the parasites had a clear seasonal occurrence.
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