We examined the role of olfaction involved in schooling of Japanese sea catfish Plotosus lineatus, and attempted to elucidate the relationship between the sensitivity to an aggregating pheromone and bodylength in reference to a reduction of the school size with growth in Japanese sea catfish. Behavioral test of preferenCe for sea water which had held their own school were carried out on 97 fish (42 to 235mm in total length), using filtrated sea water or sea water which had held another school as a control. The catfish discriminated and selected the sea water holding their own school. However, anosmic fish no longer discriminated their holding sea water, suggesting that this preference leading to a school was established by olfaction but not other sense organs including taste. No distinct change in the preference with fish growth was recognized. However, larger fish especially maturing females tended to show a lowered preference. This suggests that reduction in the constituent members of the school with growth in Japanese sea catfish was dependent upon breakaway from menace of predators or upon dispersal of maturing females from their school to avoid incest breeding.
Histological observations of the ovaries, statistical analyses of catches by trammel net, and obser vations of territorial males and egg masses by SCUBA diving were made in order to clarify the reproductive biology of the elkhorn sculpin, Alcichthys alcicornis. Ovarian development was categorized as immature (July-December), yolk accumulation (January-March), copulation and spawning (April-May), or degeneration (May-June). Sections taken from mature ovaries showed A. akicornis to be a multiple spawner, ovulating and spawning several times in a single breeding season. Trammel net catches during the breeding season suggested that members of the breeding population migrate synchronously by sex from offshore depths to shallow waters, males preceding females by 1 week (in late March-mid April); females achieve initial spawning by late April. Breeding sites were found in cracks or crevices between rocks within territories established by territorial males. At least 80-100 egg masses were deposited in each territory during the overall spawning season. The occurrence or otherwise of sneaking tactics during copulation in A. alcicornis is discussed.