Abstract--The complete larval development of Metapenaeopsis dalei (Rathbun) is described from laboratory-reared larvae. The larvae were reared in a plastic container (20 L). Larvae from the first zoeal stage to the third zoeal stage were fed algae; larvae from the first mysis stage to the first postlarval stage were fed newly hatched nauplii of Artemia. The nauplii of M. dalei hatched about 20 hours after spawning. The larvae passed through six naupliar, three zoeal, and three mysis stages before the postlarval stage. About 15 days (about 347 hours) were required from hatching to the first postlarval stage. Larval morphology of M. dalei is described and compared with those of other Metapenaeopsis spp. The first nauplius stage larva of M. dalei bears a chitinous conical protuberance on the mediodistal margin of the body. The third protozoeal stage larva has five dorsomedian abdominal spines on the abdomen. The morphological characters of the first postlarva are 43 scaphognathite setae on the maxilla, three scaphocerite spines on the outer margin of antenna, and sternal plate spines: 2,2,0,1,1.
The kishi velvet shrimp, Metapenaeopsis dalei (Rathbun), inhabits coastal waters of Korea (Kim, 1977) and Japan (Kubo, 1949). Of the 26 penaeid genera comprising 215 species, the genus Metapenaeopsis is the largest with 76 species (Perez Farfante and Kensley, 1997). However, studies on the complete larval development of Metapenaeopsis spp. are few.
The mysis and postlarval stages of Metapenaeopsis mogiensis (Ratbun) and Metapenaeopsis andamanensis (Wood-Mason) and postlarval stages of Metapenaeopsis barbata (De Haan) have been partially described by Paulinose (1988) from plankton samples. Jackson et al. (1989) reared Metapenaeopsis palmensis (Haswell) in the laboratory and described all the larval stages of the species except the naupliar stages. From previous works on Indo-west Pacific penaeid larvae, they also described the important morphological characters for identification. Chong and Sasekumar (1994) studied the larval development of Metapenaeopsis stridulans (Alcock) from the egg to the first postlarval stage reared in the laboratory and prepared descriptions of all the larval stages. Ronquillo and Saisho (1997) provided descriptions and illustrative figures of the complete larval development of M. barbata and compared the morphological characters of the larval stages with those of several penaeid species.
The purpose of the present study is to describe the larval development of M. dalei from the egg to the postlarval stage and to compare its larval development with that of other known Metapenaeopsis larvae.
Materials and methods
On 22 August 1996, gravid females of Metapenaeopsis dalei were caught by shrimp trawl in Oeyondo, Korea, and transported to the laboratory of the Taean Fish Hatchery, National Fisheries Research and Development Institute, Korea (NFRDI).
Each of them was kept in a 0.5 t container, containing filtered seawater (22.0 ° C; 32.2 [salinity]), until they spawned. On the night of 22 August 1996, a gravid female spawned, and the eggs hatched on the next day. The larvae were reared in a plastic 20-L container. Half the total volume of rearing water was changed daily with fresh seawater (24.0-26.0 ° C; 32.2-33.2...