The main theme of this article is to help new brackish tank keepers learn the basics behind keeping their organisms healthy. This article was largely inspired by the huge influx of questions I've recieved at work about Green Spotted Puffers and Mono Sebaes, and some of the misinformation currently prevelant in the hobby. I would like to start off by acknowledging Cody Schoup's informative article on brackish tanks, titled: Starting a Brackish Aquarium. This article has been around since at least 2005, when I started my first tank and was the perfect launching pad.
10 Things You Need To Know About Brackish Tanks
Photo credit: US National Oceanic and Atmospheric Administration
1. Brackish tanks are ecosystems which comprise of fish and organisms found in places where a freshwater river meets a saltwater ocean or sea. In the wild, rivers flow down (when applicable) into the ocean. Somewhere along the lines, the freshwater from the river slowly mixes and increases in salinity as it approaches the mouth to the ocean, passing through brackish environments like salt marshes and mangrove lagoons.
2. Brackish tanks require marine salt, rather than commonly sold aquarium salt. Marine salt is just that – it is salt which has (in most modern synthetic salts) been manipulated to include many extra carbonates found in seawater, such as calcium, which effects the water column’s Alkalinity, pH and gH. Marine salt produces saltwater which is chemically similar to water from the ocean, which is exactly what a brackish tank requires. Regular aquarium salt, or simply Sodium chloride, only makes up approx.. 77% of this blend and should be used for medicating freshwater fish rather than used as a means to keep brackish or marine fish alive and healthy. For more information on distinguishing these two salts, click here: Marine salt vs Aquarium salt.
3. Brackish tanks can be filled with a huge collection of fascinating fish. Cody Shoup of Badman’s Tropical Fish, commented in his article Starting a Brackish Aquarium1, “These brackish waters are home to an amazingly diverse and unique group of animals, some of which are commonly available to keep in the home aquarium. These fish include archers, scats, monos, certain livebearers, gobies, and others.” The following are a collection of images with corresponding care pages linked by clicking on the name above.
Archer Fish (Toxotes jaculatrix)
Photo credit: Ltshears, Wikipedia.
Scat (Scatophagus argus)
Photo credit: Nicolas Guerin, Wikipedia.
Green Spotted Puffer (tetraodon nigroviridis)
Photo credit: Catxx, AquariumWiki
Figure 8 Puffer (Tetraodon biocellatus)
Photo credit: Catxx, AquariumWiki
Mono Sebae (Monodactylus sebae)
Photo credit: LiveAquaria.com
4. True freshwater plants, like true freshwater fish, suffer from too much salt and will not tolerate brackish tanks. However, with that being said, there will be a few which can tolerate saltier conditions. Schoup explains that Java Fern and Java Moss will survive in a low end brackish tank, however, “After raising your specific gravity over 1.015, these plants will begin to die off and they should be replaced with marine algae such as Caulerpa”2. Most freshwater plants, especially those coming from low TDS and low salt, acidic water (Amazon), will not tolerate even small amounts of salt. Some fish, such as livebearers from the Yucatan estuaries of Mexico (Mollies) have evolved to live in brackish or even marine ecosystems. In general, most brackish fish can live in freshwater at the beginning of their lives, and saltwater at the end of their lives, but should spend most of their time in brackish tanks where they will feel less osmotic stress.
Laguna del Mar Muerto, one of the areas Mollies are native too. 3
Photo credit: La Mana de Cordoba.
5. Yes, that Columbian catfish you’ve always wanted belongs in brackish water! Columbian catfish/sharks are one of the most intriguing fish commonly sold in pet stores. Unfortunately, not all staff members are aware of their long term needs. While sharks can live in full freshwater as youth or juveniles, they will quickly require a higher salt content. Here is an interesting post about the Columbian sharks need for salt and the osmoregulation process, by member water_baby83 on the popular fishkeeping forum Monsterfishkeepers.com4, “…sharks have hit upon a different strategy. Instead of being less salty than the sea, sharks store certain metabolic wastes (namely, urea and trimethylamine oxide, or TMAO for short) so that their overall 'saltiness' is actually slightly greater than that of the sea. As a result, sharks do not continually lose their bodily supply of freshwater to the sea. Instead, any fresh water they need diffuses gently into their bodies through the mouth, gills, and other exposed membranes. Any excess water in a shark's body is filtered by the kidneys and excreted out an opening called the 'cloaca', located between the pelvic fins (the rearmost paired fins, behind the shark's belly). It's a very elegant solution to a significant environmental challenge. But it has its limitations.
If a typical sharks were to swim its very 'salty' body into fresh water, so much fresh water would diffuse into its tissues that the kidneys would have to work overtime in order to get rid of it all. This is a very energy-demanding process, and explains why most sharks do not enter fresh water: it's simply too much effort to keep excreting all that freshwater. But some sharks, such as the Bull Shark (Carcharhinus leucas), are able to enter fresh water for prolonged periods. They achieve this neat trick by greatly reducing their bodily concentrations of urea and TMAO. Even so, a Bull Shark in fresh water is slightly saltier than its surrounding environment, so that it must continually excrete excess water in the form of dilute urine. In total, some 43 species of sharks and rays spend at least part of their lives in fresh water. But one family of South American stingrays -- the so-called River Stingrays (Potamotrygonidae) -- evolved from a marine ancestor to become thoroughly adapted to living in fresh water. So much so, in fact, that their bodies have lost the ability to manufacture urea and -- if placed in full-strength seawater, they quickly die. Though CS may start life in fresher waters, once they are older, they no longer to adapt as well to variations, and will need a more brackish setting. You need to acclimate them SLOWLY, raising the salinity very slightly over a period of several weeks for the best results. It's not too complicated, but you do need to be patient, as in the wild, they do not just up and leave the freshwater and jump into salt. They hang around inlets, and such, gaining a tolerance, and acclimating themselves. Just take your time, and do it slowly, and make sure you watch for any signs of stress. Good luck.”
6. Brackish tanks can be planted, too. Many people think of brackish tanks as bare aquariums due to the lack of brackish plants found in pet stores. But there certainly are some options for those who are willing to look around or purchase online. Some common ones, which survive up to 1.005 specific gravity5 include Vals, Onion Plants, Banana plants and some Crypts (ie ciliata). Above 1.005, Java Fern and Moss, Mangroves (not aquatic but can be utilized in a properly set up aquarium), and many sea grasses will survive in lower salinity tanks such as a brackish tank. For more information on Seagrasses, I recommend visiting Tom Barr and the crew at ReefCentral.com’s Marine Plants and Macroalgae Forum.
7. There are 3 main brackish habitats that often work extremely well in aquariums. To list them here would be simple, but I’d rather point you towards Schoup’s article once again, as he’s done a great job breaking down stocking, water parameters and even provides a small glimpse of each habitat.
8. Brackish ecosystems are largely consisting of small to sugarfine size substrates. The following is a picture of a mangrove lagoon underwater6:
This sandy substrate is common in most brackish ecosystems and the aquarist should attempt to recreate this by using a similar substrate. Sand has a way of compacting, and causing anoxic area (areas of low to no oxygen) which can cause all kinds of trouble for a new aquarists, so stick to a shallow 1.5’’ sandbed or less, and be sure to stir it up on occasion. Besides sand, calcium based aragonite or crush coral mixes are also acceptable and will provide some buffering for the tank, aiding in it’s stability. These substrates can also be vacuumed and easily maintained.
9. Salinity changes can be used as a positive, but no sudden shocks. In the wild, brackish systems have salinity fluctuations due to rain, tide, and flooding. These can be simulated in the aquarium, but I recommend starting with very small and gradual shifts. Avoid large shifts of more than 0.002 per day. Remember, when saltwater evaporates, the salt itself stays in the tank so brackish tanks should be topped off with freshwater only.
10. Be weary of hydrometers. Hydrometers are a useful tool, but I would not consider them to be all that reliable. After filling the hydrometer, check that there are no air bubbles inside the chamber, especially on the arm itself. Flick the unit if there are bubbles until they dislodge. Flush with warm freshwater after each use. If possible, purchase a calibration fluid to check accuracy.
SOURCES
AMS. Fishforums.net (http://www.fishforum...ackish-aquaria/)
Catxx. AquariumWiki (http://theaquariumwi...ffer_1-4958.jpg and http://www.theaquari...8pufferfish.jpg)
Fishbase.org (http://fishbase.org/...esName=sphenops)
Guerin, Nicolas. Wikipedia (http://en.wikipedia....claw_zoo)-2.JPG)
Lamana de Cordoba (http://www.lmcordoba...ta.php?ni=34374)
LiveAquaria.com
Ltshears. Wikipedia (http://en.wikipedia....rcherFish01.jpg)
PetInfoClub.com (6. http://www.petinfocl...h_aquarium.aspx)
Shoup, Cody, Badman's Tropical Fish (http://badmanstropic...h/brackish.html)
water_baby83. Monsterfishkeepers.com (http://www.monsterfi...hp/t-10302.html)
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