Other behavior

Feeding behavior gets a page in the "Fish nutrition" folder.
 
Stereotyped behavior. When an animal is feeling its confinement, it can resort to meaningless repetitive behavior, as when a caged tiger endlessly paces one wall, turning at each corner with precisely the same movements. Sometimes fish will fall into patterns of such stereotyped behavior. Stereotyped behavior can be a symptom of low-level stress. Fish are sensitively tuned to chemicals and hard-wired to escape from toxins. Even low levels of ammonia can stress a fish so that it makes repetitive escape movements, repeatedly bumping against the glass. I think there's even a possible link between stereotyped behavior and nitrate levels. I've noticed that, if I've been a little slow with the water changes, and nitrates have risen above about 40 ppm, some fishes will face the glass and develop a stereotyped routine, of circular or back-and-forth movements, with their nose against the glass pane. A water change interrupts the behavior. I've noticed this in Siamese Algae-eaters, barbs and also in Apistos. Robert T Ricketts in AquaSource attributes this "pacing the wall" behavior to "active hunters inadequately housed. "
 
If this behavior occurs in your tank, you can control the location where it is done in part by current. Rearranging your filter outlet flows can cause relocation of the selected site. But to get rid of it altogether requires moving the fish to a much larger and more complex setup, in my experience."
 
Target fish. (Compare Dither fish below) . Konrad Lorenz, in his book On Aggression, defined pair bonding as the stage when the male and female turn from mutual aggression to cooperation in directing their joint aggression towards an outside individual. In your aquarium that will be a small population of harmless shoaling fish, so that aggression is not focused on a single stranger. Target fish help focus a developing pair bond by offering a mild threat or challenge to the breeding territory. Some successful breeders of large territorial fish protect the target fish behind a plastic screen barrier; even if its fins don't get ripped, the situation is still stressful for the targeted fish
 
Target fish are not there to take abuse. Take care that the target fish aren't being damaged; with large aggressive cichlids, the target fish can be protected by a grating partition and still be effective in reinforcing the pair bond.
 
Fishkeepers who misunderstand a target fishes' role, often imagine that an aggressive individual fish, such as one of the mating pair, has a certain fixed quantity of anger, a sort of reservoir, and that it can somehow be expended in violence against an interloper, thus sparing its spawning partner. Even respectable biologists used to think along these lines.
 
Dither fish (unlike Target fish) reassure a shy fish that it's safe to come out from a hidey hole. If confident fish  are dithering about in the open, there is likely to be no predator nearby: so runs the fish logic. Good ditherers are fearless and active fish that tend to school, such as danios, tetras, or barbs. A shy dither fish is counterproductive, to say the least.