Graduate School of Fisheries Sciences, Hokkaido University, Hakodate, Hokkaido 041-8611, Japan
The feeding habits of Japanese flounder Paralichthys olivaceus larvae were investigated in Mutsu Bay, northern Japan. Larvae were collected by horizontal hauls with a plankton net (80 cm diameter and 0.35 mm mesh aperture) or MTD nets (56 cm diameter and 0.35 mm mesh aperture) at two stations in the bay from June 15 to June 29, in 1999 and May 30 to June 28, in 2001. At the first feeding stage, larvae fed mainly on tintinids, Undella sp., copepod nauplii, mainly Paracalanus sp., and Oikopleura sp. Food items for larger larvae were Oikopleura sp. and copepodites. The larvae with nauplii in the diet at the first feeding stage were more frequently found in 2001 (55%) than in 1999 (16%). In the environment, the abundance in the biovolume of Paracalanus nauplii in 2001 was about 1.2-2.0 times larger than that in 1999. Allometric growth curves between notochord length and body weight show that larvae were plumper in 2001 than those in 1999. Therefore, the feeding intensity and the somatic condition of larval Japanese flounder at the initial feeding stage would be vulnerable to change in naupliar abundance in the environment.