If you want to keep something really exciting in your tropical aquarium the chances are that you've thought about piranhas. With a reputation as one of the world's most fearsome fish, the piranha is actually quite shy by nature, but will become more confident if properly cared for. A naturally hardy fish, it makes a good choice for the beginner aquarist - provided, of course, that basic safety precautions are taken.

Piranhas are relatively big fish, growing to as much as twelve inches in length, and they need a fair amount of space to swim around, so make sure your aquarium is large enough for them. When young they prefer to live in shoals, but as they get older they become more solitary and territorial. Older piranhas who have not been raised together should not be kept together. They can be kept with larger fish of other species, but may occasionally bite them. Once they are fully grown they will generally leave much smaller fish alone, especially if they have been trained to accept non-live food.

Loaches are among the most intriguing and entertaining fish available for the tropical aquarium. Intelligent playful and highly sociable, they provide an entirely different fishkeeping experience.

The first thing you'll notice about loaches is their unusual shape. Slender and eel-like, they are bottom dwelling fish, but they also enjoy climbing on rocks and plants and, if the right support is available, will sometimes climb part-way out of the water to bask. 

They also enjoy digging (so be careful you don't have any heavy rocks of ornaments which might get knocked over and injure them) and, if your aquarium has a soft substrate, will sometimes burrow. Their curiosity sometimes extends to trying to get out of the tank, so make sure you have a secure hood - these fish don't just jump, they sometimes try to open things!

Loaches are happiest in groups of three or more, though they will also shoal with other bottom-dwelling fish if those fish are amenable to it. They are very tactile and use their well developed barbels to touch one another affectionately.

Naturally, this is sometimes construed as an attack by other kinds of fish, which can lead to trouble, so they are best not kept with shy fish who are prone to stress or with aggressive fish who may start fights as a result.

With their unusual shape and beautiful shimmering scales discus are widely admired, but many aquarists are nervous about keeping them because they have a reputation for being difficult to look after. 

In fact, so long as you take good basic care with water quality and provide them with plenty of space, discus can thrive in the aquarium and can prove delightful fish to keep.Despite being members of the cichlid family, discus are best suited to soft, slightly acidic water. 

Native to freshwater springs and small streams, they need extremely clean water and will benefit from weekly partial water changes in the aquarium. You must have good filtration in order to keep them successfully. 

Relatively peaceful fish, they can do well in a community aquarium, but will thrive only with other fish who need similar conditions. Neon tetra get along well with discus, despite their difference in size, as do many species of catfish.

Because of their aggressive temperament they should not be kept with fish much smaller than themselves, but they can get along well in community tanks with fish like cichlids, oscars and plecos.