Aquarium fish are frequently kept in inadequate conditions that cause chronic stress, disease, and shortened lifespans from misunderstood welfare requirements.
Fish in undersized tanks cannot express natural swimming, territorial, and social behaviours, causing chronic stress that compromises immunity and increases disease susceptibility. Species kept singly when naturally social, or vice versa for territorial species, experience chronic stress from inappropriate social conditions. Improper water chemistry causes physiological stress that may be experienced as constant discomfort. Disease from poor water quality causes prolonged suffering in fish that are difficult to treat and often die before appropriate care is given. The scientific case for fish sentience is now strong enough to take their welfare needs seriously.