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Peter McKane
Title: Fish Acclimatisation

Summary: A detailed article about how to introduce new fish to an aquarium.
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Date first published: August 2005
Publication: Peter's website:
Reprinted from Aquarticles:
Sept. 2005: Posted by Mike Talbot, of England, as part of the database of his msn group: africanriftlakecichlids.
January 2006: Posted by Ján Hvizdák, of Kozice, Slovakia, on his website
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Fish Acclimatization

by Peter McKane
of England. From his website

The acclimatization of fish is an incredibly important process. Without it, fish that you introduce to your tank, whether it is a new setup or not, will become severely stressed and as a result may die or suffer severely reduced life expectancy. The process itself is incredibly simple, and if more people stuck to it, then many stress related deaths could be avoided.

Acclimatization begins where you first pick up the fish. From the moment they leave their tank, whether it is from a private supplier, a local fish store or even out of the box that they were delivered in, the fish must be kept as still as possible. If you are driving home with your fish, then hold the fish in its box or bag in the air between your legs. This means that any sudden acceleration or stopping will mean that the fish will sway and not be bumped up against the side of their container. The container should also let in as little light as possible. Most fish stores will wrap a bag containing fish in old newspaper, and this is an excellent practice because dark conditions make fish suffer less from stress.

If your journey back to the new tank for the fish is long, make sure that you open the container at least once every thirty minutes to let in fresh air. This is not sufficient to keep a fish happily alive for more than a few hours, because the container used to transport the fish will be far below the recommended size to house the fish permanently. This reason alone is enough to discourage buying fish that are delivered by post, unless they are sent via a courier to arrive preferably within 12 hours, but no more than 24 hours.

Dark conditions make it much less likely to stress fish to the point of weakening their immune system and making them susceptible to illness. Make sure that throughout the process of moving the fish into its new aquarium, the fish sees as little light as possible. Draw the curtains in the room and turn off any aquarium lights. Obviously you will need to be able to see what you are doing, but as long as at least the aquarium lights are turned off, then your fish will feel a lot happier about everything that is going on.

Temperature difference
Fish generally are very intolerant of rapid changes in their water conditions. A sudden change in pH or KH can result in stress and illness. However, by far the most important factor to consider is the change in temperature. A five degree sudden change in temperature can be enough to cause most fish so much stress that they are likely to die within a day of the change. For this reason, we will always float fish.

If you have ever seen your local fish store on the day of a delivery, you will hopefully see that there are many bags with fish floating in the tanks that they will be kept in until sold. Fish stores have a lot to lose if a whole batch of fish suddenly dies from stress, and so they will usually take care to acclimatize their fish correctly. Floating fish in bags or containers such as plastic boxes or breeding isolators means that they will gradually become accustomed to the temperature of the tank. A fish should be floated in darkness for at least fifteen minutes. I personally float my fish for anything up to thirty minutes. While it seems to make sense to float a fish for as long as possible, to reduce the stress of transportation and temperature difference, don't forget that the fish is currently in a rather cramped environment, and a balance of introduction speed to temperature acclimatization needs to be found. For me, thirty minutes is perfect. It is also important to remember that even if the water in the transport container feels like it is the same temperature as your own tank, your fish will like a rest from the transport itself, and temperature is not the only thing to consider.

Water Conditions
Now that your new addition is used to the temperature of your aquarium, you will need to gradually add small amounts of water from your tank to the transport container. If the transport container currently has a fish in four cups of water, then you should add one cup of water from your own tank to this container every five to ten minutes. You should aim to add, gradually, the same volume of water that is in your transport container from your own tank over a period of fifteen to twenty minutes. Once you have done this, then it is on to the method of introduction.

Many fish stores use the same water and a large filtration system over many tanks. This is more efficient for the store and easier to maintain than having many individually filtered tanks, and as long as there is no disease in the water, fish kept in a system like this tend to thrive. However, always be aware that a single sick fish in one tank in a fish store could indicate that the disease is present in all tanks. The last thing you want to do is introduce a stressed and disease carrying fish into your own setup. The disease itself may already be present in your own tank, like ich, but will be dormant because your fish are healthy and resistant. Keep in mind that your new additions, no matter how well transported, will be stressed, and therefore vulnerable.

It is always recommended that if you are introducing a new fish to your tank that you do not introduce any new water to your own setup. Even if the fish you introduce is perfectly healthy, the water may not be. Therefore, once you have gone through the temperature and water condition acclimatization, you should catch your fish in a net and then add them to your tank. You should also leave the lights off for at least an hour after doing this.

This particular step must, however, be ignored for some types of fish. Puffers, for example, must never be taken out of water because if they inhale air it is usually fatal. In the case of fish that must be kept under water at all times, it is recommended that you introduce as little of the new source water into your tank as possible. You should aim to add twice the volume of water in the transport container from your own tank, and then use a cup just big enough to hold the fish safely to take it from its transport container and add it to your setup.

If you are a keeper of marine fish, then your fish are not only valuable as lives under your responsibility, but also in terms of your wallet. Those aquarists who keep expensive fish swear by enforcing a strict quarantine of all new fish. This is done by introducing the newly acquired fish in a separate tank setup designed to be as close to the final conditions that the fish will eventually be introduced to, but without the risk of contaminating existing stock with diseases. Even if your fish are not expensive in terms of how much they cost, you may want to consider doing this for all fish that you wish to introduce into your tank setups. It is, by far, the safest way of ensuring that you do not inadvertently introduce disease into your precious tanks. However, many aquarists, especially beginners will not have the equipment necessary for this, and as such will simply have to take the risk of introducing fish directly into their target tank.

This whole process, not including transportation, usually takes between thirty minutes to an hour. Considering the benefits of healthy and stress-free fish, it is something that can hardly be seen as a chore. Please follow these guidelines each time you introduce fish to your tank, but do remember that no matter what precautions you take, fish do stress easily, and if it is a weak fish then there is little that you can do to keep it alive. Make sure to pick the strongest and healthiest fish from the stock that is available to you, and if there are only sick or weak fish to choose from, then wait for a new delivery. This sounds harsh, as the fish you leave behind may very well die and not be sold, but this will only encourage breeders and fish stores to house their fish properly and keep their fish as healthy as possible.