Use of the first dorsal fin ray as a lure by the bothid flouder, Asterorhombus intermedius

Abstract

We investigated the feeding behavior and use as a lure of the first dorsal fin ray of the bothi flounder, Asterorhombus intermedius toward prey goby fish (Acentrogobius pflaumii, Favonigobius gymnauchen) in Kagoshima, Japan. The distal two thirds of the first dorsal fin ray of the flounder bears membranous flaps. In an aquarium with 1 or 2 prey fish, the flounder waved its first dorsal fin ray repeatedly around the mouth when a prey fish approached. The effect of amputating the first dorsal fin ray on attracting prey fish was then tested. The number of prey fish that approached decreased significantly after amputation. Thus the movement and morphology of the first dorsal fin ray of the flounder mimics an annelid worm or crustacean, and acts as a lure for prey fish.