A ROLE OF OLFACTION IN SCHOOLING OF JAPAN ESE SEA CATFISH, PLOTOSUS-LINEATUS

We examined the role of olfaction involved in schooling of Japanese se a catfish Plotosus lineatus, and attempted to elucidate the relationsh ip between the sensitivity to an aggregating pheromone and body length in reference to a reduction of the school size with growth in Japanes e sea catfish. Behavioral test of preference for sea water which had h eld their own school were carried out on 97 fish (42 to 235 nun in tot al length), using filtrated sea water or sea water which had held anot her school as a control. The catfish discriminated and selected the se a water holding their own school. However, anosmic fish no longer disc riminated their holding sea water, suggesting that this preference lea ding to a school was established by olfaction but not other sense orga ns including taste. No distinct change in the preference with fish gro wth was recognized. However, larger fish especially maturing females t ended to show a lowered preference. This suggests that reduction in th e constituent members of the school with growth in Japanese sea catfis h was dependent upon breakaway from menace of predators or upon disper sal of maturing females from their school to avoid incest breeding.