Growth and Survival of Japanese Littleneck Clam Ruditapes philippinarum in Cage Test Related to the Sharpness Index

Abstract

Three cage tests for the growth and survival of Japanese littleneck clam juveniles were conducted on the tidal flat of Kuzuma along the coast of Kisarazu district in Chiba Prefecture, Tokyo Bay, and the sharpness index defined as width/length of shell was examined. The area having good conditions for juvenile growth was not consistent with that for a high survival rate, and juveniles with a high survival rate did not always grow faster than those with a low survival rate.
Juveniles on the offshore side grew faster than those on the shoreside, but the juvenile survival rate in the intermediate zone of the flat was higher than those on the offshore and shore sides. The juveniles having a high sharpness index tended to show a high survival rate. At the same age, the juveniles with a high sharpness index grew faster than or equal to those with a low sharpness index. But as the sharpness index approached the maximum value on the tidal flat, the shell growth of the juveniles was less than those of younger clams and the sharpness index was lower.