Your first consideration in selecting a species should be whether or not you are qualified to maintain that animal in a healthy condition for the balance of its life. More and more, environmental ethics also require that you consider whether or not you can successfully breed certain species in captivity, especially those that are collected from the wild or that face an uncertain future there.

You must also carefully research the legality of your proposed acquisition. The fact that an animal is offered for sale in a pet store, at a trade show, or on the Internet is not an indication that you can legally keep that animal in your home. Increasingly, governments and regulatory agencies around the world are moving to protect the animals and plants under their jurisdictions. In the United States, an extremely complicated maze of city, state, county, federal, and international regulations is in place to assure that endangered species and those of special concern are not brought into the marketplace. These rules and regulations change frequently, so it is virtually impossible for the average person to keep abreast of the situation. In the United States, if you are a prospective purchaser of an animal that seems of questionable legality, you should call your state's Department of Environmental Conservation, and also the regional office of the United States Fish and Wildlife Service. The staff at both of these agencies will be immensely helpful in advising you concerning the laws or regulations that may be in place regarding that particular species.

Once you have determined that you are competent to care for the animal that interests you and that the species is legal to purchase, several other factors should be considered. You may wish to choose animals that are of interest to you because of their behavior or natural history, as opposed to those that are merely attractive in appearance. By focusing on such creatures, you will be assured of maintaining your long-term interest and, hopefully, of learning more about the animals as time goes on.

A variety of practical considerations are also important to bear in mind. While heating an aquarium is a fairly straightforward and simple matter, the same cannot be said for cooling them. Although aquarium chillers are commercially available, most are expensive to purchase and operate and they are often designed for rather large systems. Therefore, it may be difficult or at least extremely impractical to keep temperate or cold-water species if you live in an area with a very warm climate.

You should also calculate not only the overall expenses involved in pursuing the hobby in general but also those connected with the species of particular interest to you. Animals that require complicated life-support systems or diets that are difficult to procure may place an inordinate strain upon your budget. Similarly, time constraints should figure into your decisionmaking process. Animal species whose care places a heavy burden upon your time will soon rob you of any enjoyment inherent in keeping them and most likely will cause your interest to wane.

Certain species of invertebrates and fish are extremely specialized feeders. Those that require a varied diet of live food may be difficult to maintain unless you live in close proximity to a habitat where you can collect their natural food items. Seahorses, for example, are particularly sought after favorites by many marine aquarists. However, these animals are confirmed live-food specialists, and the most readily available diet offered to them — brine shrimp — is unsuitable as a sole diet for all except, possibly, the dwarf seahorse (Hippocampus zosterae). If you plan to acquire these and similar creatures, such as pipefish, you really do need to live in an area where you can collect a variety of small marine organisms for them to feed on. In the alternative, you would need to establish thriving colonies of several species of such organisms, such as mysid shrimp, grass shrimp, and amphipods.

Although some animals that feed upon live food in the wild, including certain individual seahorses, can be trained to accept nonliving food items, most require a close approximation of their natural diet if they are to survive. Despite the increased availability of a variety of live food animals to hobbyists, and advances in their culture in captivity, most live-food specialists require far more dietary variety than can be supplied by the average hobbyist.

If you do decide to keep delicate creatures, whether freshwater or marine, focus on those whose habits are well understood and where others have had some success in their husbandry. It is also important that you have access to hobbyists or professionals who will share with you the secrets of their successes. You may wish to maintain the slightly larger species of a group of animals that is delicate in general, as their more generously sized mouths may allow them to accommodate a wider variety of food items. Tiny animals that specialize in unique diets are particularly difficult to maintain in captivity.

Always strive to acquire fish and invertebrates that that have been bred in captivity, as opposed to those that are collected from the wild. It is often a fairly simple matter to ascertain this, especially if you choose to purchase from private dealers who maintain breeding colonies of animals within their homes or shops. Magazines, the Internet, aquarium societies, and public aquariums are also valuable sources of information as to which animals are being bred in captivity.

The purchase of captive bred animals is not only an environmentally sound way to approach your hobby, but it is also a favorable decision from a practical point of view. Captive bred individuals, even those of species that are notoriously difficult to keep in captivity, always adjust more easily to life in the aquarium. They also present the best prospects for the hobbyist if he or she is to maintain the animals for long periods of time, learn about their life cycles, and, possibly, to have them reproduce successfully. An additional benefit of this route is that the breeder from whom you purchase your animals will be able to give you a wealth of information that may be unavailable elsewhere, and will increase your likelihood of success.