If you take a quick look at this species they don't seem like aquarium fishes. They are large and highly predatory. But then again, these are qualities that attract some, like me! If you've been keeping aquariums for a while and have the room to keep large predatory fishes I recommend you try these fish, but not until you've done your homework and know the gars' requirements and what you are getting yourself into.
Species of gar:
Florida spotted gar, Lepisosteus platyrhinchus
A highly varied species of gar. Has more spots on its body and a shorter snout than many other gars. Easily mistaken for spotted gar.
Spotted gar, Lepisosteus oculatus
Long snout and spots. Spots to a higher degree towards the posterior of its body. Easily mistaken for Florida spotted gar.
Shortnosed gar, Lepisosteus platostomus
The shortnosed gar can be identified by its short snout, and by the lack of teeth rows in the upper jaw like the alligator gar, and the lack of spots on its body.
Long-nosed gar, Lepisosteus osseus
The long-nosed gar is, as the name suggests, identified by its long slender snout, and also by its slender body.
Alligator gar, Atractosteus spatula
The alligator gar has a short broad snout and two big rows of teeth in the upper jaw. This species is spotted on the posterior part of the body and to a lesser extent on other parts of the body.
Tropical gar, Atractosteus tropicus
A very rare species.
Manfari or Cuban gar, Atractosteus tristoechus
Looks very similar to the alligator gar and since it is very rare in the trade you can usually assume that your gar is an alligator gar and not a Cuban gar unless otherwise stated. The Cuban gar has a broader snout and lacks pattern on its body.
Beside these species there are a number of hybrids such as the crocodile gar.
Spotted, Florida and short-nosed gars are smaller than the other species and may be more suitable for aquariums. They usually don't grow larger than 2 feet in aquariums. Long-nosed and alligator gars grow to a very large size and larger ponds are recommended if you'd like to keep fully grown specimens. So if you don't have (or plan on getting) a large pond, stay with the smaller species. Even with the smaller species you are still going to need a rather large aquarium. The tropical gar also is possible to keep in aquariums as it doesn't grow as large; however this species is very hard to find. The Cuban gar is a red-list endangered species and shouldn't be kept even if you somehow find one.
In aquariums gars are quite demanding and require a lot of space and clean water. I recommend you to use as big a tank as you can for your gar, and I wouldn't recommend keeping gars in an aquarium smaller than 200 Gallon/720 L. And that should be considered a minimum; a 400 gallon/1400 L tank is preferable.
The tank should be decorated in accordance with gar behaviour. Gars are ambush predators, and as such they appreciate hiding places from where they can stalk their prey. This is however not essential. They are very friendly towards fish that are too big to be eaten. In the wild gars often live in loose schools and if you have the space you may successfully keep several gars together, in fact I would recommend this.
Gars can be kept with most fishes that are too big to be considered food and not too aggressive. However, gars should never live with plecos. Plecos sometimes suck on gars and cause infections, and since gars are very sensitive to most medicines these infections may be very hard to treat.
Regarding water, the most important thing is keeping the water clean and well circulated. Gars accept most pH or hardness levels. Temperature can range from 60 to 90 degrees Fahrenheit (16 - 30 degrees Celsius). Gars breathe air and should be left with a few inches of space at the top of the tank to allow them to breathe atmospheric air.
Gars usually accept most kinds of living prey that are large enough. Feeders such as goldfish provide a good base for their diet but should never be the only thing they are fed, since this would not provide the gars with all necessary nutrition. Their diet should be diverse, and this can be achieved by also feeding minnows, shrimps etc. It is also possible to train gars to accept frozen foods and pellets.
Gars cannot be sexed externally. They have occasionally been breed in aquariums but are more frequently bred in ponds or are wild caught.
William berg has more then 20 years of aquarium experience and writes for aquatic community - a website with information on everything from crayfish to cichlids.