ABSTRACT This study describes the prevalence of a parasitic bopyrid isopod, Parapenaeon consolidatum, on Metapenaeopsis dalei and its effect on host growth and reproduction. The prevalence of P. consolidatum increased with shrimp size, from 27.3% at 5 mm CL to 68.4% at 16 mm CL. Lengths of female bopyrids and that of their hosts were positively correlated. This indicated that the bopyrid stays continuously with its host and is not detached when the host molts. Morphometric analyses indicated that parasitized male and female shrimp have slightly lower body weight and length than nonparasitized shrimp of the same carapace length. The gonadosomatic index was higher for nonparasitized than for parasitized female shrimp. Growth of the petasma, the copulatory organ of male shrimp, was significantly affected by the parasite.

KEY WORDS: Metapenaeopsis dalei, Purapenaeon cosolidatum, growth, reproduction

INTRODUCTION

The kishi velvet shrimp, Metapenaeopsis dalei (Rathbun), is distributed throughout the coastal waters of Korea, Japan, and China in sandy muddy substrates at 30-130 m depth (Kim 1977, Hayashi 1992). With seasonal warming of the waters starting in April, the shrimp begin to migrate from deeper water to the coastal area. They are exploited commercially in Korea from April to October, using shrimp trawl and stow nets (Cha 1997). Metapenaeopsis dalei exhibit higher burrowing rates than other penaeid shrimp (Sakaji 1995). Owens (1987) reported that the bopyrid isopod Parapenaeon consolidatum Richardson is a parasite on M. dalei from Japanese waters. However, little is known about the effects of this parasite on growth and reproduction of its host.

Bopyrids live on shrimp, brachyurans, and anomurans and cause a conspicuous bulge of the branchiostegite (Dall et al. 1990). Owens and Glazebrook (1985) showed that bopyrids on penaeids grow with their hosts and have a similar longevity, although there is some loss of parasites as the prawns approach asymptotic length. Some studies hypothesized a relationship between a bopyrid and its host because of a highly positive correlation between the sizes of female bopyrids and their shrimp hosts (see Beck 1980: Schuldt & Rodrigues Capitulo 1985). Cash and Bauer (1993) reported that Probopyrus pandalicola (Packard) remain on and grow synchronously with Palaemonetes pugio Holthuis; video recording has shown that reproductive activities of the parasites are synchronized with host molting.

Both growth and reproduction of shrimps can be affected by bopyrids. Abu-Hakima (1984) showed that parasitized male Penaeus semisulcatus De Haan grew to the same size as nonparasitized females but that host reproduction was totally inhibited. She also showed that a petasma, the male copulatory organ, was not formed in parasitized male shrimp. Chu & Leong (1996) indicated that parasitized male and female shrimp have slightly lower average body weights than nonparasitized shrimps of the same carapace length. Dawson (1958) reported that in the Arabian Gulf, only P. semisulcatus larger than 100 mm TL (total length) were parasitized with bopyrids. Mathews et al. (1988) found low parasite prevalence among P. semisulcatus of 14-18 mm CL (carapace length) by Epipenaeon elegans Chopra; prevalence increased up to a prawn size of...