Introducing a new fish to your tank

Congratulations, you're expecting a pair of bouncing baby goldfish! Or perhaps you're adding a trio of tetras to your warmwater tank. No matter the size or species of your new fish, you can ease the transition to their new home and give them a proper welcome by taking a few simple precautions.

Adding fish to saltwater tanks and freshwater tanks

Successful introductions start at the aquarium store. Make sure the fish you purchase are in good condition. Healthy fish swim steadily with erect fins and have well-filled-out body contours. Do not buy any animal who is inactive or emaciated, or has any bumps, lumps, open wounds or split fins. Also, determine beforehand if the fish you have chosen will get along with each other--or are they best kept with their own species? If they are not yet fully grown, is your tank large enough to accommodate their maximum potential size? Will they thrive in the same water conditions as your current fish?

At the time of purchase, your new fish will be put in sturdy plastic bags filled with water from the tank they've been residing in. Take care when transporting them home, and try to keep the bags insulated so the water stays as warm as possible.

Once home, shut off the aquarium lights and float the bags in the tank for at least 15 to 30 minutes. This will ensure that the temperatures in the bag and in the tank are approximately the same. Next, you may want to open the bag while it is afloat, remove a small amount of water and add some from your tank. This will allow your new friends an even more gradual adjustment to the water conditions in their new home. If you wish, you can repeat this process three to four times. When you are ready, gently net the fish out of the bag and place them in the aquarium. Introducing foreign water into the aquarium could increase the chances of transmitting certain diseases.

Water conditions when adding fish to a new saltwater of freshwater tank

Please note that if you are setting up a new tank--one without any inhabitants--you'll need to let the water "ripen" for a week or two before adding fish. Using a biological supplement is recommended too introduce beneficial bacteria and rapidly mature the new tank. And when you are ready to introduce fish, start with just 3-4 small fish or 1-2 medium fish, ideally the hardiest of the species you plan to keep. After that, add a couple of fish every week or so until your tank is complete. If you are adding fish to an already established community, it's smart to clean the tank beforehand so the levels of waste are as low as possible.

Once you've made your successful introductions, be sure to keep up your aquarium maintenance schedule and carefully observe newcomers. If they appear listless, swim with abrupt movements or gasp at the surface of the water--all signs of illness--it is best to isolate them in a holding tank and consult your aquarist about possible problems and treatment. Other possible causes could be water condition changes, temperature shifts.