Studies on the biology of the parasitic isopod Cymothoa exigua Schioedte and Meinert, 1884 and it's relationship with the snapper Lutjanus peru (Pisces: Lutjanidae) Nichols and Murphy, 1922, from commercial catch in Michoacan

Abstract

From commercial catch of the Michoacan fishery, samples of the snapper Lutjanus penu were examined monthly (January to December 1984) for isopod parasites. A total of 236 adult individuals of Cymothoa exigua were found in 165 of the 691 snappers collected. The isopod’s life cycle is described partially, with notes about the body index, femininity index, as well as the relative fecundity, marsupial development and pre-hatch mortality. Several indices of parasite occurrence and the values of the condition factor (K) in Lutjanus penu, by sexes and size groups, were estimated to evaluate the effect of the host-parasite relationship. No significant differences were found in the K values, but a decreasing of the values of the occurrence indices for C. exigua was observed in relation to the fish growth. The presence of isopods in L. peru appears slightly harmful to the host, but probably increases the natural mortality rate, especially in the first years of life.