Keeping brackish aquarium

What is brackish water?

Brackish water is water which contains more sea salts than freshwater but less than the open sea. Moreover, brackish water environments are also fluctuating environments. The salinity is variable depending on the tide, the amount of freshwater entering from rivers or as rain, and the rate of evaporation. As a result many brackish water fishes are tolerant of changes in salinity, and in fact many positively benefit from similar periodic changes in aquaria.

Estuarine and low salinity environments and habitats

The environments from which brackish water fishes are collected are diverse. Estuaries are the best known. An estuary is the part of a river where it meets the sea. Typically, estuarine waters are slow and sluggish, and often very silty and fertile. As a result they are not always as attractive to look at as the clear waters of a mountain stream, but they are tremendously productive. One characteristic of estuarine ecosystems, and brackish water habitats in general, is that while productivity (the amount of food available) is high, diversity (the number of species) can be quite low compared with rivers or the sea. This apparent contradiction is because relatively few fish and invertebrates can tolerate the fluctuations in salinity. On the other hand, those animals that can live there do so in enormous numbers. Gobies, flatfishes and catfish are characteristic fishes of estuaries, ranging from the fresher waters upstream right down to the sea. A few freshwater fishes may occur in the least saline parts of the estuary (for example garpike, ropefishes and cichlids). Many marine fishes, especially as juveniles, inhabit the saltier part of the estuary (such as sea bass, flatfishes, tarpon and herring).

Another important brackish water habitat is the mangal (or mangrove swamp). Mangals are characteristic of the tropics. Some mangals develop in estuaries, while others fringe islands. Mangrove plants are some of the most remarkable plants to be found anywhere in the world. They form dense forests which support a tremendous variety of animals both above and below the surface of the water. In the canopy, monkeys, snakes and a huge variety of birds are to be found; while the aquatic roots support oysters and barnacles, as well as many fish, snails and crustaceans which live in and around the thick knots of roots and stems. Mangals have provided many good fish for the aquarist, such as mudskippers and archer fishes. The mud that collects within the mangrove roots is a prime habitat for fiddler crabs, various clams, and snails.

The temperate equivalent of the mangal is often said to be the salt marsh. These are tidal habitats, periodically covered by the sea. Salt marshes are also important habitats, especially as the feeding grounds for seabirds and fishes. Instead of trees, the major plants are grass-like. Gobies and sticklebacks are especially common in salt marshes, which are quite easy to explore and a good place to collect native fish and invertebrates for the aquarium. Unfortunately many salt marshes are threatened by agricultural or commercial development.

Common to both the tropical and temperate zones, seagrass meadows are found in shallow water. Seagrasses are true plants and not algae, but have proved to be difficult to keep in aquaria. There are many fishes and invertebrates found in sea grass meadows, perhaps the best known is the seahorse. The salinity of a seagrass meadow is rarely much below that of full strength seawater, but seagrasses do occur in lagoons and estuaries where the water is brackish.

The basic equipment for a brackish aquarium

The prospective brackish water aquarist has usually kept freshwater fishes, but there is no reason why many brackish water fish cannot be kept by the beginner. In fact, they make quite good beginners fishes for two reasons. The first is that brackish water fish are hardy, active and easy to feed. Secondly, the brackish water aquarium is essentially a marine tank in terms of hardware and maintenance, and many (but not quite all) brackish water fish can adapt readily to marine conditions. The brackish water aquarium is more forgiving than a marine or reef tank, making it an ideal stepping stone for someone who wants to keep a marine aquarium but hasn’t any experience of keeping fishes at all. A brackish water aquarium really only needs an increase in salinity to keep marine fishes in; and with extra lights and filters invertebrates can be added too.

The basic set-up is as follows:

– An all-glass tank
– A lid or hood (wood or plastic, not metal)
– A filter (air powered or electric)
– A heater (optional)
– Lighting (optional)
– A thin substrate of some sort

There are many good books on fishkeeping that describe the basics of setting up a tank; additional topics are covered in Part 2 of this FAQ.

Common and not so common brackish water fishes

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:

– Garpike
– 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.

What fish can’t be kept in a brackish water aquarium?

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).

Fishes from naturally soft and acid water will not do well in tanks with brackish water, and may slowly sicken and die. Such fishes to avoid would include most of the tetras and other characins, the cyprinids (minnows), most anabantids (gouramis), and softwater cichlids like angelfish and discus. On the other hand, cichlids, livebearers and killifish from moderately hard or hard water environments will do fine so long as the pH and hardness are kept reasonable and the salinity low. A tank with a specific gravity of around 1.005 would be acceptable to robust cichlids like blue acara and the Cetral American Cichlasoma, as well as the more adaptable killifish such as Pachypanchax playfordi. Into such a tank could be combined sailfin mollies, kribensis, and spiny eels. A few of the more hardy plants might do well in such an aquarium. Too much salt would be detrimental to the health of even robust freshwater fishes.

On the other hand there are some freshwater fishes that tolerate little or no salt at all. The Ostariophysi are an important group of freshwater fishes which are generally intolerant of salt. Within this group are such common aquarium fish as tetras, goldfish, minnows, barbs, loaches, rasboras and danios. Catfish are also members of this group, although three families of catfishes (the families Aspredinidae, Ariidae, and Plotosidae) are adapted to salt water. Salt intolerant catfish include many of the commoner sorts like as the dwarf catfishes (Callichthyidae) including the popular Corydoras catfish. Some of the larger species of sucking catfishes (Loricariidae) such as the pleco Hypostomus, are very robust and with care can be kept in slightly brackish aquaria, below a specific gravity of 1.005. Rift Valley cichlids sometimes react badly to brackish water, succumbing to “Malawi Bloat”, an often fatal dropsy-like condition.

In a strongly brackish aquarium, i.e. with a specific gravity of 1.010 or more, there is always the option of keeping some regular marine fishes. Many species of damselfish will do well, as will pufferfish, batfish and lionfish. See Part 7 of the FAQ for more on this. But many marine fishes, and practically all the commonly traded marine invertebrates, are not tolerant of salinities below that of normal sea water and should not be kept in a brackish water system. micro sd speicherkarte

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