A brief guide.

Marine fish species are far more difficult to deal with than their freshwater counterparts. Furthermore many species of aquarium fish are incompatible, or unable to be 'housed' together. Some species of fish are highly aggressive such as the male Siamese fighting fish (Betta spendens). Although very popular, these fish will fight to the death, regularly tearing out chunks of each others fins, hence why they are often found kept alone. So careful selection of fish to be included in the aquarium is essential.

So when creating your aquarium fish combinations are vital. Many fish are known not to play well together. If just starting out, species to consider may include fish such as the damselfish or clown fish (also known as the anemone fish). However, it is not only the other fish in the tank that must be considered, but also the other occupants whether they be mollusks , arthropods , plants or corals .

There are several species that should be avoided altogether. These include batfishes , sharks , rays , and seahorses .

Octopuses are rare but nice additions to aquariums. Obviously, they require larger tanks than and should not be kept with fish otherwise they will eat them. The other consideration that must be remembered when thinking about keeping one is that they can and will climb out of the tank. So a lid is necessary.