The breeding of fish and invertebrates is never as simple as placing two individuals of the opposite sex together. A host of other very important factors should be carefully considered before you embark on a breeding project. The production of eggs or young is really only the first step in this fascinating but often labor-intensive aspect of your hobby.

Animals employ a wide variety of breeding strategies and certain strategies are easier to accommodate in an aquarium than others. In general, experience with freshwater fish and invertebrates will greatly increase your chances of success with the less-studied marine species. Also, when working with freshwater species, you would be well-advised to begin with well-known live-bearers such as guppies and then go on to some of the hardy egg-layers, such as the zebra danio. Eventually, you may want to work with fish that form pairs and utilize courtship rituals, nest building, and other more complicated reproductive patterns.

Marine fish and invertebrates in general reproduce far less commonly in captivity than do freshwater fish. However, advances in this area are becoming more and more common, with over 100 species of marine fish having been bred in home aquariums to date. Marine invertebrates are less well studied, but their reproductive husbandry is also being explored by many hobbyists. One of the first marine species to be successfully bred was the dwarf seahorse, followed shortly thereafter by the ever popular clown or anemone fish, and by several species of goby and blenny. Of the marine invertebrates, only the banded coral shrimp reproduced in aquariums with any regularity in the early years of the hobby.

The hobbyist who seeks to work with marine species might consider keeping a large, hardy native species at first. Native species are more easily accommodated in terms of natural foods, light cycles, and water quality. Also, you might be more familiar with their actual habitats as a result of personal observation, a situation that will greatly increase your chances of success.

Keep in mind that young fish of all types require enormous quantities of food, usually several times each day, and that much of this food is difficult to procure. Although commercial preparations have made the hobbyist's work easier, live foods such as daphnia and infusoria are often the essential. The culture of such food items will require additional time and space. Also, while some fish species will reproduce while being fed their normal diet, many require a special conditioning period during which they should be fed a variety of live foods or fresh vegetables. See Chapter 16 for additional information on this topic.

In nearly all cases, mated pairs of fish or invertebrates will fare better in a tank by themselves. Even those fish species that breed in large aggregations will do so more successfully if other species are excluded from their aquarium. This will necessitate a separate aquarium as well as additional life-support systems, lights, and related accessories.

Also to be considered is the fact that many animals will not reproduce unless they are given suitably-sized aquariums. Some species need the security of a tank that approaches the size of their natural territory if they are to breed successfully. Water depth is also a consideration, especially for certain marine fish. As always, careful research is required, but you should be aware that maintaining animals in breeding condition may be quite different from keeping them for exhibit purposes.

Aquarists who have bred both marine and freshwater fish and invertebrate species often comment that they achieve greater successes, overall, by maintaining animals in somewhat “naturalistic” aquariums. A heavy growth of plants or algae seems almost essential for many species. Filtration systems employing live rock and sand, with little water disturbance from external filters, are also mentioned time and again as helpful or even necessary. You may wish to learn more about such aquarium systems when seeking to breed delicate species.

Fish and even invertebrates can be extremely picky when it comes to a mate choice. In some cases, you may notice that two fish in a dealer's tank or in your own will spend a good deal of time together or engage in what appears to be courtship rituals. Such fish are ideal candidates for transference into a separate aquarium for breeding purposes. Pairs of freshwater angelfish are often identified in this matter.

Although little is known about the natural or captive reproduction of most invertebrates, a few species do appear to establish long-term pair bonds. Banded coral shrimp, for example, seem to be particularly devoted to each other, with males having been observed to feed pregnant females. As usual, close observation will be your key ally in identifying a pair. A surprising number of fish can change their sexes in response to a variety of environmental conditions. Obviously, this may complicate the task of identifying a pair. However, in some cases this reproductive strategy may simplify matters. Marine clownfish, or anemone fish, for example, all begin life as males. The largest and most dominant in any group eventually changes sex and becomes a female. Therefore, any small group, or even any two fish, will likely provide you with a pair suitable for breeding.

A further complication to captive breeding efforts is the fact that many fish and invertebrates do not exhibit sexual dimorphism, or, more likely, aquarists have not yet learned to identify the dimorphism that does exist. In such cases, the behavior of the animals themselves may give you a clue as to whether or not they are a compatible pair. In fact, your studies of this matter may lead to reliable ways of differentiating the sexes in animals that currently baffle aquarists.

As with most endeavors involving captive animals, extensive research and discussions with serious hobbyists and professionals will increase the chances of success and will greatly increase the pleasure that you derive from the hobby.