Studies on the Social Behavior of the Blue Gourami, Trichogaster trichopterus (Pisces, Belontiidae)

Abstract

The basic social organization of nonreproductive blue gouramis is a fairly stable dominance hierarchy. For the most part, fish of both sexes confine themselves to nonagonistic maintenance activities. Overt aggression tends to appear at feeding times, when new fish are introduced into an established hierarchy, or at certain periods when 2 well-balanced fish test each other. The imminent commencement of a reproductive cycle also increases the frequency of agonistic behavior, as dominant fish nip and chase subordinates increasingly. The onset of a reproductive period in males usually is marked by increasing aggressiveness, a gradually developing tendency to remain in or near a certain part of the tank, and frequently the initiation of a bubble-blowing behavior that eventually results in the construction of a bubble nest at the air-water interface. The floating bubble nest serves as a depository for the fertilized eggs when spawning occurs. When fully in the territorial phase, males are highly aggressive in defending a definite area in which the nest usually has been constructed. Encounters between adjacent territorial males contain a complex series of motor patterns, several of which seem to be markedly ritualized. Most territorial males respond to the sexual stimulus provided by the presence of a ripe female with another series of behavioral patterns which collectively could be called courtship activities. These activities appear to attract and/or stimulate the female and facilitate successful spawning, at least during the early phases of the spawning cycle. The end result of courtship of the male is the presence of the female immediately under the nest in a position suitable for the consummatory sexual actions. The spawning sequence is triggered by one or more bites that the female directs at the side of the male. This usually results in the male dropping down beneath the female so that his dorsum touches or nearly touches her breast. He then moves back and forth in a fairly rhythmical movement I call rubbing. To my knowledge, rubbing is not present in other anabantoid species. After rubbing for a minute or so, the male begins to curve his body and revolve in a horizontal plane. The female moves into the center of this curve and is clasped by the male. The clasped pair turnsover so that the female is belly up, and strong contractions of the body muscles cause the fish to vibrate visibly before the sex elements are released. After a brief period during which both fish appear stunned (swimming inhibition), the male chases the female away and begins to retrieve eggs which he blows up into the bubble nest. After some time, the male either seeks out the female or she comes up to the nest again, and the spawning sequence is repeated. After several spawnings, the female usually ceases further sexual activity, although on occasion, the male terminates a spawning series by becoming highly aggressive and preventing the female from approaching the nest.