How to Introduce Fish to Your Aquarium

For most hobbyists the most exciting part of setting up a new aquarium is buying and introducing the fish. Even when the filtration is mature, there is some debate as to whether you should add your fish all at once or in small batches over the ensuing weeks.

With freshwater tropicals, if the ‘daily feed’ maturation method has been used, all or the bulk of the population can be added at one time, provided they are fed only very lightly while the filter takes up the load. This also avoids the need for quarantining successive batches. With delicate marine organisms, however, one or two at a time is the golden rule. You can also put some grade a indian almond leaves in your aquarium.

When deciding what fishes to buy, remember not to exceed the permissible stocking density of the aquarium, and, in particular, take into account the fact that many fish are sold as young specimens and will grow! All calculations must therefore be made on the ultimate size of the fish, not size when purchased. Of course, the aquarist does not have to keep purchasing fish until the maximum stocking level is reached, but may decide to cease stocking at any time to maintain a particular display community.

aquarium fish How to Introduce Fish to Your Aquarium

Bagging and transportation

Fishes are normally packed in clear plastic bags, often in a brown paper outer or carrier bag so that the fish cannot see out and panic at finding themselves suspended in mid-air! Never carry fishes home ‘unshielded’, unless you want them to die immediately of shock.

Some fish bags have their corners rounded so that fishes cannot get trapped and injured in the ‘point’. If ordinary bags are used, it is worth asking to have bags ‘cornered’, i.e. the corners tied with rubber bands or taped off. A dealer who does this without your asking is a very good dealer indeed.

If you are travelling a long distance (say, over an hour), ask for the fish to be double-bagged, with oxygen. This will ensure that they arrive in good condition and not stressed by a shortage of oxygen in the travelling water. Two bags, one inside the other, will also safeguard against leaks. If you don’t already have one, ask the dealer for a polystyrene fish box. Place the bags in it, packing tiny spaces with crumpled newspaper to avoid excessive heal loss (or overheating) and disturbance while travelling.


On arriving at home, turn off the tank lights and undo the bags, then suspend them in the top of the aquarium while the water temperatures equalize. Some people may tell you to mix some aquarium water with that in the bag to avoid chemical shock, but with freshwater fish this achieves nothing, as it takes them 24 to 72 hours to adjust to any change in water chemistry, and any major change is likely to prove fatal whatever you do at this stage. You must ensure that there is no such major change. Try to keep stress to a minimum -the acclimatization period should be as short as possible, and the bags undone before they are placed in the tank (so they don’t have to be taken out again).

Once the temperatures have equalized, gently upend each bag so that the fish can swim out. Make sure that they have till done so!

Most fish will swim around quite happily in their new home after leaving the bag and the lights can be switched back on after an hour or so. However, a few may be stressed enough to lie on the bottom or hide among the plants. On no account should they be disturbed by prodding or poking. Leave them in peace, with the lights out, and it is very likely that they will be fine on inspection the next morning.

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