As mentioned previously, you should ask the seller details about of how your prospective pet has been maintained. Knowing as much as you can about factors like the temperature and salinity to which the animal has been exposed will greatly increase your chances of successfully acclimatizing it to your own aquarium. Of course, only purchase specimens that have been kept under the environmental conditions that are required for optimal health. If the water quality parameters of the store or dealer are acceptable, but vary somewhat from your own, ask the seller for an extra quantity of water so that you can very slowly adjust the animal to the changes that it will need to face.

Fish and invertebrates are generally transported in plastic bags. Approximately two-thirds of the bag should be filled with air (many stores and dealers now keep oxygen tanks on hand for this purpose) and one-third with water from the aquarium in which the organism has been kept. If the fish or invertebrate is to be kept in the bag for a considerable amount of time, ask the seller to use a large bag and, if possible, to fill it with oxygen. If the animal will be exposed to extremely hot or cold temperatures during transit, be sure to bring along an insulated box of Styrofoam or a similar material to help offset the temperature. You may also wish to consider a hot-water bottle or a cold pack as well.

In all cases, the animal that you purchase should be kept in the dark on its journey to your home. Of course, take precautions not to shake or drop the shipping container, and to shield it from strong vibrations such as those that might be experienced in a car traveling over a rough road surface.

The actual introduction of the animal into the aquarium is best done in a dimly lit room to reduce the animal's stress levels. You may also wish to feed the current aquarium inhabitants prior to introducing a new creature, to lessen their aggression toward or interest in their new tank mate. The plastic bag in which your animal has been transported should be floated in the aquarium for fifteen to twenty minutes to allow the temperature within the bag to equalize with that in your aquarium. To avoid the shock associated with changes in pH, specific gravity, or other water parameters, you should add a bit of water from your tank to the bag every five minutes or so.

When dealing with particularly delicate creatures, or with any animals that have been housed in water that differs considerably in makeup from your own, you should use a drip system of acclimatization. This process may require more water than is typically sent home with the creature, so be sure to ask the retailer for extra water if you anticipate such a need. To do this, place the animals, with their original water, in a plastic bucket. Run a length of airline tubing from your aquarium to the bucket and allow the water to drip into it slowly. The rate of flow from the aquarium into the holding container can be easily adjusted via the use of plastic valves, available at most pet stores, or even with simple paper clips or binder clips. Be sure to take occasional readings of the various water quality parameters and adjust the flow of water from the tank into the holding bucket accordingly.

Newly introduced fish and invertebrates should not be exposed to bright lights for the first few hours after their introduction into your aquarium. They need not be kept in total darkness, but it is best to leave the main aquarium light off and instead utilize the room light at this stage. Your new pets should, of course, be observed carefully for their first few days in their new home. Be especially careful to see that they are eating and that they are getting along well with the other animals in your aquarium.

As has been mentioned previously, it may be prudent to quarantine certain new animals, especially those that are particularly rare or delicate, or those that are to be introduced into a collection housing such creatures.

Again, you must weigh the value of such a quarantine period against the disadvantage in exposing the fish or invertebrate to two separate acclimatization periods. A quarantine tank that is maintained with environmental conditions that are essentially the same as in the main aquarium will go a long way toward easing the adjustment of new creatures to your collection.

Avoid the temptation to add large numbers of fish or invertebrates to your aquarium at one time. Animals should, ideally, be introduced one at a time, and the introduction process should spread over as long a time as is possible. This will allow your filtration system to adjust to the new load on its capacity and will ease the stress on the animals already living in the aquarium.