normal behaviour for siamese fighting fishHere we investigated how nest keeping, male Siamese fighting fish use two alternative forms of displays, gill flaring and fin spreading, towards intruders during a number of reproductive phases; before BB and after bubble nest constructing, and after spawning AS, and hatching AH. Males were more competitive against male than female intruders and the extent of aggression modified considerably between reproductive phases. Gill flaring, the more energetically costly display, was the dominant preliminary display towards male and feminine intruders in BB, AS, AH phases. However, protecting males switched to fin spreading after prolonged publicity to intruders. The effects suggest that Siamese fighting fish use gill flaring as an acute reaction as a way to defend their territory; this response may get replaced by fin spreading as a protracted response, probably to minimize the active costs during the contest. This week, the Fish of the Week title goes to the superbly flamboyant Siamese Fighting Fish Betta splendens, that is native to the Mekong Basin of Laos, Cambodia, Vietnam and Thailand.