The blue gourami (Trichogaster trichopterus), does not appear to go through a ritualized prespawning behavior sequence. The female is apparently brought into a state of sexual activity as a result of the presence of a dark, nest building male. Spawning is initiated by the female and it consists of a stereotyped cycle of behavioral events. In the majority of cases, male castration results in the cessation of nest building, a reduction of colour change, a partial atrophy of the morphological secondary sexual characteristics (S.S.C.), and the absence of spawning. Treatment with methyl testosterone brings back all of these characteristics. In a few cases, castration resulted in only a partial reduction of nest-building, colour change and morphological secondary sexual characteristics and the retention of spawning. It is tentatively suggested that there may be an extragonadal source of androgen. It seems the physical act of spawning is necessary to trigger full parental behavior regardless of gonadal condition. Agonistic behavior is not apparently affected by castration. Methyl testosterone given to unoperated females resulted in male-like agonistic behavior, coloration, secondary sexual characteristics and some evidence of nest building. / Science, Faculty of / Zoology, Department of / Graduate

Laboratory experiments examined now aggressive behavior, use of space, activity and breathing frequency were affected by the number of fish competing for a concentrated, renewing, intermittent food source. Total aggression rate per fish and the proportion of long chases decreased in larger groups and increased during short periods in which food was unavailable. The proportional use of the area near the food source was maximal at intermediate group sizes suggesting that use of the feeding area was reduced by aggressive defense at low densities and by passive interference at high densities. Air-breathing frequency tended to be lower when food was available than when it was not, suggesting that gouramis reduce their use of atmospheric oxygen when it may result in loss of food to competitors. Group size affects the pattern of food competition more through economic resource defense than through passive interference.

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