During the breeding season, the sight of a red belly on any other stickleback triggers aggressive behavior in a male stickleback. this is called:

The aggressive behavior in male stickleback in called a fixed action pattern. Fixed action pattern is a sequence or series of actions that occur as an innate behavior in animals. The actions are triggered by external stimulus called the sign stimulus which involve sight of something.They trigger an unchangeable pattern of behavior. In the case of the stickleback, once the male stickleback sees the red belly of the female stickleback, a signal is sent to the brain that it is mating season and they start being aggressive.

This is called innate behavior. 
Innate behavior is a natural gene controlling behavior that occurs in an organism without the need for preliminary learning or experience. This type of behavior is demonstrated by all members of a species in a very similar way whenever they are exposed to a certain stimulus. From the question given, the aggressive behavior being triggered in a male stickleback when it sees a red belly on any other stickleback during the breeding season is called innate behavior. 

Wetlands form where water and land meet. a lake with a wetland fringe can fill in with decayed plant and animal material to become a wet meadow. a pond can fill in to become a bog or fen. sediment can fill in a river marsh to become a swamp.flooding of coastal lowlands from rising sea levels has created broad coastal marshes that are protected from wave action by barrier islands or reefs. coastal wetlands also form when rivers deposit sediment as they reach the ocean. plants then take root and hold the soil firm against the forces of tides and waves.