Now for something a lot smaller. Brachygobius (Bumblebee gobies) are suitable for those of you who cannot keep a large brackish water aquarium, because they will be quite happy in a 60 x 30 x 30 cm (24 x 12 x 12 in) tank. Although these fishes are small, we do not recommend using anything smaller than this because it is more difficult to maintain good water conditions in a small body of water.
No one can fail to be intrigued by a fish that shoots down its prey, and in public aquaria there is almost always a small crowd of people around the archer fish tank, all hoping that the fishes will perform.
Mudskippers are notoriously difficult to maintain in captivity because of the demands they place on the aquarist. Species imported include Periophthalmus barbarus, Periophthalmus catonensis, and Periophthalmus kaelreukeri, but these names are often confused-and identification is uncertain.
The halfbeaks occur in southeast Asia and are found in both fresh and brackish environments. Most of those available in aquatic outlets have been acclimatized to freshwater conditions (with maybe a level teaspoonful of salt per 4.5 litres/1 gallon), so you should have no problems with them
If you are looking for something a little out of the ordinary you may like to consider the leaf fishes. These members of the family Nandidae occur in South America, Africa, and Asia.
At some time or other you may wish to try your hand at keeping spiny eels, members of the family Mastacembelidae. Despite their common name they are not related to the true eels, but just have a similar long thin shape.
The anabantids are a large group of fishes found in the tropical waters of Africa and Asia. They are best known for their ability to breathe atmospheric air. The organ that they use for this is known as the labyrinth (hence the common name labyrinth fishes) and is situated on either side of the head in the gill cavity directly above the gills. The fish takes in air from above the water surface and passes it into two chambers, each of which has a rosette-like structure which looks not unlike a sponge. This has a very good supply of blood vessels close to the surface of the structure, and therefore the fish is able to absorb oxygen from the air.
There are few more diverse invertebrate groups than the mollusks. Marine gastropod mollusks possess a protective shell and a “foot” for locomotion, just like the land snails.
Starfish are the best-known echinoderms, but the group also features feather and brittle stars, as well as sea urchins and sea cucumbers. While they vary in shape, all these creatures have an internal body structure formed from calcium and tube feet that enable them to move over the seabed.
