ANALYSIS OF THE PARASITIC COPEPOD SPECIES RICHNESS AMONG MEDITERRANEAN FISH

The Mediterranean ichthyofauna is composed of 652 species belonging to 405 genera and 117 families. Among these, 182 were studied for their parasitic copepods. The analysis of all the works conducted on these c rustacea yielded 226 species distributed in 88 genera and 20 families. For each fish species we have established a file providing the specie s name of the fish, its family, its geographical distribution within t he Mediterranean and some of its bio-ecological characteristics. Withi n each file, all the parasitic copepod species reported on each host s pecies were listed. This allowed to know the species richness (SR) of these hosts. We thus produced 182 fries within which 226 copepod speci es are distributed. A program was created under the Hypercard software , in order to analyse our data. Two parameters were studied. The first one is the mean species richness (MSR), which corresponds to the mean of the different SR found on the different host species. The second i s the parasite-host ratio (P/H), which is the ratio of the number of c opepod species by the number of host species. These parameters are cal culated by our program for all the 182 species of Mediterranean fishes retained in our investigation, on the first hand, and, on the second hand, for one particular group of fish species. We used the following variables to investigate their correlations with copepod species richn ess: taxonomy-fish families, genera and species; biometry-maximal size of the adult fish; eco-ethology-mode of life (benthic, pelagic or nec tonic), displacements (sedentary, migratory with environmental change, or migratory without environmental change), behaviour (solitary or gr egarious). Other variables (colour, food, reproduction, abundance, dis tribution area) were also analysed but did not reveal any clear correl ation. Providing that our study does not rely on quantitative (prevale nce, intensity) but qualitative basis our aim was only to reveal some tendencies. These tendencies are as follows: (1) In many cases, parasi te and host phylogeny seem to play an important role. There are fish f amilies with copepods and families with few species of these parasites . The phyletic constraints could be due to the morphological character istics of the habitat (e.g. structure of the gills) or biological/ecol ogical characteristics that we were unable to identify. (2) It appears that the presence in a same environment of related fish species (e.g. several species of the same genus, or numerous genera of the same fam ily) is correlated with high parasite richness. A likely explanation i s that such situations favours alternated processes of lateral transfe rs and speciation. (3) Some eco-ethological criteria seem to favour th e establishment of a large parasite species richness. It should be not ed for instance that Mediterranean fishes the most often infected with copepods are generally nectonic or pelagic, migratory, and gregarious species. (C) 1998 Elsevier Science B.V. All rights reserved.