Brackish-intolerant Aquarium Fish

Freshwater Fish

Obviously the best fish for a brackish water aquarium are fish that naturally come from brackish water, but it often happens that an aquarist wants to mix some brackish water species into a regular community tank (or vice versa). For the most part this is a bad idea -- most of the commonly traded community fish are not salt-tolerant and will not do well in brackish water. With a very few exceptions, tetras, barbs, danios, rasboras, gouramis, and loaches should not be kept in the brackish water aquarium.

Catfish are a mixed bag in terms of salt-tolerance. There are of course several families with species that enter the sea, including the Aspredinidae, Ariidae, Bagridae, Pangasiidae and Plotosiidae. But the two families most frequently kept by aquarists are the Callicthyidae and the Loricariidae, and these families are made up almost entirely salt-intolerant catfishes.Corydoras species as well as most of the plecs and bristlenose catfish should not be kept in the brackish water aquarium. Exceptional members of these two families include some species of Hypostomus such as Hypostomus plecostomus known to be slightly salt-tolerant (SG to 1.005) and the brown hoplo Hoplosternum littorale, a species commonly found in brackish water in the wild and easily maintained at SG 1.005 or even slightly higher.

Some cichlids are quite salt tolerant, of which more is said elsewhere in this FAQ, but the Rift Valley cichlids apparently react badly to brackish water, succumbing to “Malawi Bloat”, a potentially fatal dropsy-like condition. Cichlids from soft water environments, including angelfish, are equally intolerant of salt.

Livebearers and killifish from hard, alkaline waters often do fine in slightly brackish water. So while things like platies, goodeids and pupfish might not come from brackish waters in the wild, they can be expected to adapt successfully to a specific gravity as high as SG 1.005.

Marine Fish

Some traded marine fish will tolerate low salinity conditions for extended periods, even indefinitely, but in general this should not be assumed. If you want to add marine species to your brackish aquarium, do your research carefully and make absolutely sure the species being offered in the shop is what you think it is.

Commonly Traded Species of Brackish Water Fish

Although brackish water aquaria are less frequently created than either fresh or marine ones, brackish water fish are far from uncommon and in fact include some of the hobby’s staples. A few of the commonest and most desirable inmates for the general brackish water aquarium are:

• Sailfin and other mollies
• Monos
• Scats
• Archerfish
• Pufferfish
• Cichlids

Less frequently seen, but very desirable for the aquarist eager to try something a bit different, are the predators of the coastal swamps, estuaries and mangroves, such as:

• Gar
• Shark catfish
• Sleeper gobies
• Spiny eels

And a few oddballs quite unlike anything else:

• Anableps
• Mudskippers

Even the aquarist with only minimal space can enjoy the fishes which are happy in small tanks (24 inches in length or less):

• Killifish
• Gobies
• Glassfish
• Pipefish

All these fishes and more are covered in later parts of the FAQ.

Breeding

Some brackish water fishes can be bred in the aquarium. The easiest fishes are the livebearers like guppies and mollies, closely followed by the hardy cichlids like kribensis. These species will breed even in community tanks, and provided the young aren’t eaten, you will soon have a problem finding homes for your new fish!

Where breeding can be obtained easily, brief notes are included in each species entry for the interested; but as a rule most aquarium books cover these species. Baensch’s Aquarium Atlas is probably the best European reference book for many unfamiliar species. TFH also publish numerous fish breeding books. A useful primer to fish breeding is Fish Breeding by Chris Andrews, part of the ‘Interpet Guide To...’ series.

On the other hand, many brackish water fishes have not been regularly spawned in captivity. Fishes such as Monodactylus sebae have been bred only on a very occasional basis while the breeding habits of others, like archerfish, are completely unknown. In many cases this is probably because the fishes are large and up till now insufficient tank space and number of individuals have been kept. As aquaria become easier to manage and people keep larger tanks, hopefully this problem will be overcome. Even so, some ‘triggering factor’ may be lacking, such as changes in salinity or temperature. With such fishes there is plenty of scope for experimentation.

If you want to breed aquarium fishes, perhaps the most reliable species to begin with are:

• Kribensis -- egg layer, guards spawn and fry; fry easy to feed
• Orange chromides -- egg layer, guards spawn and fry; fry need small live foods
• Bumblebee gobies -- egg layer, guards spawn and fry; fry need small live foods
• Mollies -- livebearers, fry big and easy to feed
• Halfbeaks -- livebearers, pregnant females somewhat delicate, but fry easy to raise

It is almost always best to keep fishes you want to breed in a separate tank with the minimum of decoration. Try to keep the tank as clean as possible, and remove any uneaten food. Use a good filter, but make sure the flow isn’t so strong it would suck up eggs or the baby fishes (fry). Provide nesting sites for those fishes that need one, such as a small flower pot turned on its side (ideal for gobies and dwarf cichlids). Feed the parents on the best food you can; frozen bloodworms and crustaceans are ideal conditioning foods and will complement a good quality flake food nicely. In the case of livebearers, remove the male after the female has become pregnant. Generally female livebearers will ignore their offspring after they have been born. Cichlids can be left together as pairs if they are coexisting, although if one or other of the parents is not behaving well it can be taken back to the community tank. Be aware that in the case of many cichlids the first or second broods are not always successfully raised. Sometimes the parents eat the eggs or fry. Don’t worry -- they eventually get it right! Male gobies are often in sole charge of the brood, in which case the female can be removed if she is being attacked. In all cases it is important to give the fishes, particularly the females, a rest between breeding cycles.