2 PARASITIC COPEPODS, PSEUDOMYICOLA-SPINOSUS AND MODIOLICOLA-GRACILIS, ASSOCIATED WITH EDIBLE MUSSELS, MYTILUS-GALLOPROVINCIALIS AND MYTILUS-CALIFORNIANUS, FROM BAJA-CALIFORNIA, NW MEXICO

Mussel culture and fisheries are two increasing activities in Baja Cal ifornia, NW Mexico. One of the risks for these activities is the prese nce of harmful parasites like certain copepod species. This study was carried out to determine the parasitic copepods associated with edible mussels, Mytilus galloprovincialis Lmk. and Mytilus californianus Con rad, from Baja California, NW Mexico, and to establish certain aspects of their distribution, temporal fluctuation, and damage to their host . The study was carried out at sites of contrasting environmental cond itions: exposed rocky shores, protected shores, protected and polluted areas, and culture area. Two species of parasitic copepods were found inhabiting the mantle cavity and gills of mussels: Pseudomyicola spin osus Raffaele and Monticelli (Mycolidae) and Modiolicola gracilis Wils on (Clausidiidae). This is the first record of these copepods in Mexic an waters. M. gracilis was found in M. galloprovincialis and M. califo rnianus from all localities studied in numbers from 0 to 5 individuals per host and a maximum prevalence of 26.66% in the first species, and from 0 to 15 specimens per mussel and a maximum prevalence of 70% in the second species. Its presence was relatively constant through the y ear, with a slight increase in autumn and winter. P. spinosus, by cont rast, was scarce or absent in M. californianus and M. galloprovinciali s from exposed rocky shore environments. Its number and prevalence wer e low in the mussel culture area. However, it was very abundant in M. galloprovincialis from the protected and polluted environments, where its numbers ranged from 0 to 59 copepods per mussel and a prevalence o f 100%. Rates of infestation in mussels increased in autumn. Macroscop ical damages associated with the presence of copepods were not detecte d, and the histopathologic analysis did not reveal any damage to the t issues of the host. However, there were more parasites in larger musse ls, and most parasitized mussels showed a low condition index. P. spin osus could be considered a potential threat to the mussel culture.