A dither fish is an active yet non-aggressive fish or a school of fish that prefer open water. They are kept in a tank with shy, reclusive fish. The choice of a proper dither fish species will depend on common needs regarding water conditions (PH, temperature, hardness), size (one doesn’t want the main fish to eat the dither fish), feeding assertiveness (one doesn’t want the either fish to get all the goodies), and the typically occupied water levels (it is best if the main fish and the dither fish prefer different strata of the tank’s water). Dither fish need to have their needs met too. Schooling fish kept in abnormally small numbers will also hide and then your dither will need a dither! – not really, schooling fish just need more of their own kind to feel safe enough to come out into the open.

One wants to give aquarium fish what they would find in nature; be it cave like enclosures, heavy greenery or rock piles. They use these objects for comfort and breeding. They also use them for hiding (they hide in what they perceive to be an unknown, therefore potentially dangerous situation). If they hide all the time it not only keeps the fish keeper from observing their more interesting behaviors but it may even prevent them from obtaining adequate nutrition.

Cichlids especially benefit by the use of dither fish. Although most cichlids are known to be aggressive they also hide most of the time in novel situations (like a new tank). They are very unhappy if they are not provided with the evolutionary props they need. Dither fish bring them out of hiding for observation and feeding, make them feel safe (“if those crazy neons don’t get eaten I guess I won’t either”) and frequently induce breeding behaviors.

In my current tank (40 gallon fresh, mostly Amazonian) I have a pair Blue German Rams I'm hoping will decide to make babies.... They were hiding so much at first I thought they were dead. I keep a heavily furnished tank with caves, shelf features, tunnels, and lots of plants so there are plenty of place for small cichlids to hide in. I got a school of neons and suddenly the shy German Rams are coming out into the open without me having to remove any of the props. Yea! They are so pretty.

The Rams not only came out of hiding, they spawned. The eggs mostly fungused (new parents often lose the first clutch) but I found 2 free swimming fry in the upper plant layer which I am now growing on in a floating fry tank. The problem is, I don't know if they are Rams or guppies, which I also keep in the same tank. Only time or a more experienced fish keeper will tell....

personal experience and this wonderful article: