The Guppy is arguably the most popular and well-known aquarium fish, largely due to the wide array of colour varieties, active nature, and reputed ease of keeping and hardy nature. The Guppy has built up a reputation for being very tough, hardy and an ideal first fish and is still recommended and sold as such in many shops. Although 10 years ago this may have been true, today it is far from the truth. The Guppy has undergone years of intensive breeding to produce the staggering number of forms and colours available today, unfortunately a side effect of intensive breeding is a lack of natural immunity and an overall weaker fish. Most Guppies on sale today are in fact very weak and prone to bacterial problems, which can wipe out an entire tank of guppies in days. It is still possible to obtain good specimens but it is very difficult to tell from appearance alone. Guppies should only be placed in a mature tank (they are not suitable as first fish), ideally with hard water, some aquarium salt added and hiding spots amongst hardy plants. Males will chase females so there should be several females to every male. Alternatively, many aquarists prefer to keep just males. Guppies will breed easily and the surviving offspring are often stronger than the adults. The young males mature at 2 months, and females at 3 months and are capable of breeding. Some Guppies have a tendency to nip at slow moving long finned fish.