PARASITIC ISOPODS AS POPULATION INDICATORS IN THE HORSE MACKEREL (NICHOLS, 1920) TRACHURUS SYMMETRICUS MURPHYI (PISCES: CARANGIDAE) OFF THE CHILEAN COAST

Abstract

It was assessed whether the parasitism by the isopods Ceratothoa spp. Dana 1853 could be useful indicators of populations of the horse mackerel Trachurus symmetricus murphyi (Nichols, 1920) off Chile. Eight hundred and one Ceratothoa spp. specimens were collected from the oral cavity and gilí chamber of 900 T. s. murphyi individuáis sampled monthly near Iquique (19°S-21°30'S; 70° 25'W-71°30'W) and Talcahuano (35°S-39°S; 72°15'W-74° 30' W) from january to october, 1990. Another 793 specimens of isopods were collected from 289 individuáis T. s. murphyi sampled from july to october of the same year, from the vicinity of Caldera (27°04'S; 70° 50'W) and Coquimbo (29° 30'S; 71°22'W). We found two isopod species, Ceratothoa gaudichaudii (Milne-Edwards, 1840) and Ceratothoa trigonocephala (Leach, 1818) in similar proportions in all localities. We compared between fishing areas the body size composition, proportion of females with brood in different developmental stages, and the relationship between the íecundity and the body size for each isopod species. C. trigonocephala had a higher fecundity and larger body size than C. gaudichaudii. The comparisons showed significant differences in each isopod species for the most distant localities. The extent to which these differences indícate different populations of the T. s. murphyi inhabiting waters off north and south-central Chile is discussed.