There are many species of synodontis, and there are many hybrids, crossbreeds between the species which pop up as well, quite often in pet shops. Synodontis appear to quite happily and readily crossbreed, to the chagrin of purists who do not approve of such abominations.

Unless you have a very common species, it may be difficult to tell if what you have is a hybrid or not. There are currently well over 100 different identifies species of synodontis, and more than one syno has been misidentified as a hybrid when it was, in fact a new species.

Whether you care if your synodontis is a hybrid or not will depend on whether you intend to attempt breeding (a very noble goal indeed, given the difficulty of breeding synodontis,) or whether you are paying a premium for a 'pure' fish.

If you are trying to identify whether or not a synodontis is pure, pay special attention to fin shape, size and coloration, to the nature of the barbs around the mouth, to the overall body shape of the fish and to its markings. If your synodontis seems to have the characteristics of more than one species, there is a fairly decent chance that it is a hybrid.

If you really want to know, this article from Planet Catfish is an excellent in depth guide to identifying hybrid synodontis.

These are synodontis with shark like fins which have made them very popular indeed. They can command quite high prices both in pet stores and out of them. These synos grow to around 12 centimeters, so they are not terribly large, and if you have the funds, you can quite happily keep several of them in a 90 gallon tank.

They are also known as the cuckoo synodontis as they have a habit of eating the eggs of other fish and depositing their own in place for the other fish to tend as they grow.

A much deeper bodied synodontis, the synodontis eruptus is also known as the featherfin squeaker because off its beautiful feathered dorsal fin and the fact that it can produce a high pitched squeaking with it. These fish grow up to 20 centimeters, though 15 to 17 is more common, and have been reported as being more aggressive than other catfish.

A native of Lake Malawi, synodontis njassae is a pretty catfish with lovely coloration which can vary widely from fish to fish. Some specimens may have many spots covering their body, others have but a few. Some keepers break these into large and small spotted varieties. They grow to around 20 centimeters.

Monsters, these synodontis can grow over two feet in length. Not at all recommended unless you have a very, very large fish tank, even 100 gallons won't cut it with one of these fish when they reach maturity.

A peaceful synodontis species, these do not grow much over 12 centimeters. Unlike other species of synodontis, these have been bred in captivity relatively easily, but prefer to live and spawn in groups, so a pair may not spawn alone. These are easily confused with multipunctatus, however they sport a white trim which is not present in the multipuncatus. They tend to be quite expensive.

Quite common, these synos reach just four inches in length, which makes them the perfect catfish for a smaller aquarium. They are known widely as the 'upside down catfish'. They reach around 10 centimeters, or four inches and are very pretty and entertaining to watch as they defy gravity. It is best to keep this type of synodontis in groups of three or more.