Abstract
Katano pointed out that smaller individuals of Opsariichthys platypus and Nipponocypris temminckii occasionally leave the region where Opsariichthys platypus and Candidia temminckii swim in order to avoid attacks by larger individuals of Opsariichthys platypus and Candidia temminckii. Onitsuka pointed out that Opsariichthys platypus avoid Carassius auratus langsdorfii and also that Candidia temminckii avoid Carassius auratus langsdorfii besides Opsariichthys platypus which is larger than 80 mm of body length. However, there are few study of the behavior characteristic of the fish to another fish with different body length. In this study, the behavior characteristics of Opsariichthys platypus that have different body length against Plecoglossus altivelis altivelis in static water was analyzed. It was found that Opsariichthys platypus avoid action against Plecoglossus altivelis altivelis. This tendency becomes small as Opsariichthys platypus body length becomes large.
