Some aquarium fish can become very shy and timid in the aquarium environment, often hiding away and not feeding. This type of behaviour may be due to stress incurred during transport or by a distrust of the strange environment that the fish has found itself in.
One way to increase the confidence of such fish, and encourage them to explore their environment and start feeding, is to introduce 'dither fish'. Dither fish are normally small groups of shoaling fish that are active, peaceful, and confident. When introduced into the aquarium the dither fish will quite happily swim out and about in the open waters. When the reclusive fish see this happening, it is a strong sign that the environment is safe, and they often follow suit by emerging, exploring, and feeding.