Social isolation increases social display after priming in Betta splendens but decreases aggressive readiness.

We socially isolated adult, male Siamese fighting fish for 0 to 7 weeks but avoided sensory deprivation, and then measured aggressive display as the fish responded to a series of novel models. Isolates displayed much more strongly than non-isolates to the last model of the series, and display intensity became monotonically stronger with longer social isolation. By contrast, display to the first model seen after isolation was weaker the longer the social isolation. A second experiment compared responses of fish after three weeks during which controls displayed to a conspecific for two minutes every two days, while isolates saw a complex visual stimulus which did not release display. Again, isolates had depressed display readiness, but higher display rates once they were primed. This result supports the hypothesis that social isolation has two effects on aggressive display in Betta, causing decreasing readiness to display, but leading to greater display rates once fish are 'primed'. We discuss two models which predict these phenomena, and show that one of them suggests a new understanding of the function of motivational increases when aggression is 'dammed up'. Methodological issues relevant for examining the rodent behavior literature in the light of the new model are discussed.