Pufferfish are commonly used in freshwater, brackish water and saltwater aquariums all around the world. Most species of pufferfish seem to be quite intelligent, quickly learning to recognize their owners and often becoming tame enough to be hand fed. Pufferfish are notoriously intolerant of high nitrate levels and low oxygen concentrations. The tank requirements of pufferfish include clean water, regular water changes, plenty of swimming space, and preferably soft sand for digging. All pufferfish need good, clean water. In the case of brackish water species, the aquarists must also ensure that the water is hard, alkaline and sufficiently saline. Pufferfish are sensitive to dirty water, and should be kept in mature tanks with good filtration, and weekly water changes of at least 25% are essential. The diet items are selected according to the pufferfish species maintained. Overfeeding pufferfish causes a variety of problems, the chief of which is deteriorating water quality.