The aim of this thesis is to study morphology, morphometry, infection levels and host specificity of the mesoparasite Lerneaocera lusci towards some demersal fish species in the Belgian coastal area (southern North Sea). In the first chapter of the thesis a literature review is given: the study area is described, and detailed accounts of the biology of Callionymus spp., Trisopterus spp., and Pomatoschistus spp., final hosts for L. lusci are presented. Subsequently, the biology of the parasite and the host specificity towards its final host are described in detail. The role of Callionymus lyra and C. reticulatus in the life cycle of L. lusci is dealt with in chapter 6. It was found that C. lyra is heavily infected with L. lusci in one sampling site in the Belgian coastal area in June 1991 (prevalence = 34 %: intensity = 1.67). A morphological study (scanning electron microscopy) and a morphometric study (canonical discriminance analysis) of L. lusci are presented in Chapter 7. Based on these results a distinction was made between L. lusci f. lusci, L.lusci f.minuta, L. lusci f. lyra and L. branchialis. It is assumed that genetic differences, host species and site of attachment all determine the shape of the parasites. The presence of antennary processes is characteristic for L. lusci. In the last chapter (8), host specificity indices for L. lusci were calculated. Two indices of Rohde (1982) were compared with two new indices, which take into account the host density and the egg production. The high values for these indices were attributed to the fact that the majority of parasites have a preference for one particular host species (Trisopterus luscus). However, it was assumed that Callionymus lyra probably plays an important role in the life cycle of L. lusci. C. reticulatus and T. minutus are less important definitive hosts for L. lusci. |
