Why do formal aquariums separate different kinds of fish into exhibits?

Formal aquariums separate different kinds of fish into specific exhibits primarily to accommodate the diverse and specialized environmental requirements of various aquatic organisms.1

Maintaining aquatic life requires careful control over factors such as water quality, temperature, and the management of metabolic wastes. Because different species have unique physiological needs—ranging from specific salt concentrations and respiratory gas levels to distinct dietary and habitat requirements—grouping them into separate tanks allows curators to tailor the environment to the specific needs of each species.12

Furthermore, modern aquariums strive to illustrate the natural environment of their specimens. By creating distinct habitats, these institutions can better manage disease treatment, nutrition, and the complex water systems necessary to keep diverse animals healthy, which would be difficult or impossible to achieve in a single, large community tank.31