They have evolved structures on their fins that look very much like eggs. These egg-mimics can attract females to nest sites even though no eggs are present. Although not always this spectacular, other amazing behaviors are shown by North American fishes, and many of these behaviors are known only because they have been observed in aquarium-held fishes. This depressingly large number of endangered fishes exists because people do not care or know enough to demand that land be developed in a way that protects habitat for our native plants and animals. The more that we know about our native fishes, the more we will appreciate them for their beauty and their habits, and the more we will want to protect their environments.
Scientists make excellent use of aquarium observations.
In fact, we would know far less about our native fishes if we did not keep them in aquaria. Aquarists enjoy keeping fishes, but our native fishes are the more significant beneficiaries of this activity.