How to Introduce Fish to an Aquarium
Part of the secret of successful fish-keeping is to buy healthy fish to start with. Just like any other animal, healthy fish actually look healthy. Examine the fish in the dealer’s tank carefully. Look for those which are brightly colored and bold with erect fins; avoid small or stunted fish. If possible, ask for them to be fed while you watch so that you can be sure they are feeding well. And make sure that the dealer catches the one you actually want.
Your fish will be put into water in a plastic bag, which is then inflated with oxygen and tied off with a rubber band. The temperature of the water will soon begin to drop, so you must protect the bag from cold. Wrap it up in a scarf or, if it is small enough, put it under your coat to keep it warm. Experienced aquarists carry fish in containers packed with insulating foam polystyrene, or even in large, wide-mouthed vacuum flasks. Get the fish home as quickly as you can to avoid chilling and shock.
When you get the fish home, do not rush to tip them into the tank. Turn out the tank lights to keep the fish calm, and float the sealed plastic bag, complete with fish, in the tank for at least30 minutes while the temperatures gradually equalize. Now open the bag and use a gentle scooping movement to introduce small amounts of tank water to the water in which the fish were carried. Do this gradually, as the pH or hardness in the dealer’s tank may have been quite different from that in your own, and the fish will need time to adjust.
When you finally tip the bag over and release the fish, they will normally dive to the bottom and hide behind plants or rocks. This is customary; it may even be several days before the fish regains their usual confidence and bright colors, and begins to feed normally.
If you are introducing new fish to an already well populated tank, follow the same procedure but, as you slowly mix tank water with that in the bag, feed the other fish. Most aquarium fish are highly territorial, and even normally peaceful fish may attack a newcomer: feeding will distract them and give the new fish a chance to settle down. This is most important with marine fish, each of which will protect its own place in the tank. It may be helpful to shift all the coral in the marine tank at the same time as introducing new fish, as this disrupts all the territories and destroys any advantage held by the original inhabitants.