Stereotyped sequence of mating behavior in the Far Eastern catfish, Silurus asotus , from Lake Biwa

Abstract

Mating behavior of the Far Eastern catfish, Silurus asotus (Siluriformes: Siluridae), was observed in a ricefield system facing the shore of Lake Biwa in mid-May to early June in 1990-1997. A set behavioral sequence similar to those of two other silurid fishes, S. biwaensis and S. lithophilus, both endemic to the Lake Biwa system, was observed: "chasing," "clinging," "enfolding" while "squeezing" by the male, and "circling" by the spawning pair. This form of mating behavior is quite different from that of S. asotus reported from the Ooi River system in Kyoto Prefecture, which mainly spawns in running water in ditches.

Reproductive ecology of the Far Eastern catfish, Silurus asotus (Siluridae), with a comparison to its two congeners in Lake Biwa, Japan

“…In S. asotus as well, inter-population variation in mating behavior has been reported among three populations (the Biwa-, Ooi-, and Fuefuki-populations) (Katano et al 1988;Yamanashi Tansuigyo Kenkyukai 1995;Maehata 2002b). Mating behavior of the Biwa-population shows a fixed sequence of actions, i.e.…”

“…Mating behavior of the Biwa-population shows a fixed sequence of actions, i.e. chasing, clinging, enfolding with squeezing by the male, and circling of the paired fish, and females are always enfolded by a single male (Maehata 2002b). The latter two populations do not show such a behavioral sequence; the process of enfolding a female's body by a male is not so stereotyped, circling by the paired fish has not been recognized, and females are often enfolded by two males (Katano et al 1988;Yamanashi Tansuigyo Kenkyukai 1995).…”

“…Spawning activity of S. asotus occurs after irrigation has been initiated (Katano et al 1988), that of S. biwaensis occurs when the shore is newly submerged by swollen waters, and that of S. lithophilus has been observed at the same site used by S. biwaensis, but irrespective of high water events (Maehata 2002a). All three species spawn in such a manner that males enfold the abdomen (or head) of females for several tens of seconds prior to ejaculation, and their eggs are scattered around the spawning site with no parental care (Katano et al 1988;Maehata et al 1990;Maehata 2001b;2002b).…”

“…It had been thought that spawning of this species occurs at night in connection with rainfall (Tomoda 1962;Miyadi et al 1983), but Katano et al (1988) reported that its spawning in the mountainous Ooi River system in Kyoto Prefecture, central Japan, occurred at midnight with no relation to rainfall. Maehata (2002b) has recently reported that mating behavior of S. asotus from Lake Biwa (Biwa-population) is always conducted in pairs, a female always being enfolded by only one male, and shows a fixed sequence of actions (i.e., chasing, clinging, enfolding with squeezing by the male, and circling of the paired fish). This sequence is basically similar to that of some other populations of the same species (Asahi River population in Japan and Lake Dongting population in China, Maehata unpublished data) that spawn in lentic water, and also those of S. biwaensis and S. lithophilus (Maehata et al 1990;Maehata 2001b), but very different from that of S. asotus from the Ooi River system (Ooipopulation) (Katano et al 1988) and the Fuefuki River system (Fuefuki-population), another location among mountains in Yamanashi Prefecture, Japan (Yamanashi Tansuigyo Kenkyukai 1995, M. Muramatsu, personal communication; Table 1).…”

“…The first of these species is widely distributed in Far-Eastern Asia and the latter two are endemic to Lake Biwa, the largest and oldest lake in Japan. They spawn in temporary, lentic waters such as ditches and rice fields (Katano et al 1988;Maehata 2002b) during the rice-planting season (in S. asotus) or along the shallow shores of a large river and lake (in S. biwaensis and S. lithophilus). Spawning activity of S. asotus occurs after irrigation has been initiated (Katano et al 1988), that of S. biwaensis occurs when the shore is newly submerged by swollen waters, and that of S. lithophilus has been observed at the same site used by S. biwaensis, but irrespective of high water events (Maehata 2002a).…”