The helminth parasites of the bullhead Cottus gobio (L.) and the stone loach Noemacheilus barbatulus (L.) from the River Avon, Hampshire

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Abstract
Specimens of Cottus gobio and Noemacheilus barbatulus from the River Avon, Hampshire, were examined between July 1970 and July 1971. Both fish were found to act as hosts for Nicolla gallica (adult), Pomphorhynchus laevis (adult) and Triaenophorus nodulosus (plerocercoid). The incidence and intensity of infection were lower in N. barbatulus than in C. gobio, and this was related to differences in host diet. A small number of N. barbatulus were also found to harbour Proteocephalus torulosus. Seasonal cycles of incidence and intensity were evident in N. gallica, with a peak occurring in the winter. P. laevis and T. nodulosus showed no such cycles. Increasing host size was associated with a higher infection of both N. gallica and P. laevis, but not T. nodulosus. The diet of the host was considered to be important in influencing this increase. Differences in host reproductive condition affected the population levels of N. gallica only, where an increased parasite burden was evident in gravid female fish. This was considered to influence the observed increase in incidence and intensity of this parasite during the winter. None of the parasites showed any seasonal maturation cycles. There was no evidence of any interactions between the parasite populations. Host diet and the availability of infective larvae were considered to be the most important features influencing the number of parasites which became established, and the rate at which this occurred. Temperature probably acted indirectly on the establishment of N. gallica, by controlling the availability of the larval stages, and also, by influencing the host reproductive condition, on the length of time for which the parasite was retained by the host.