Brackish water?

Brackish water – the word ‘brackish’ originating from the 16th century Low German word ‘brack’, meaning ‘salty’ – is created as a result of freshwater and saltwater mixing together. Most commonly, this occurs in estuaries, the tidal mouths of rivers, where river or stream water meets seawater and mixes. Other brackish water habitats include mangrove swamps and various seas and lakes, such as the Baltic and Caspian seas.

Fish species inhabiting brackish waters are generally quite tolerant, as their natural habitats are highly variable. The salinity in brackish water environments can fluctuate anywhere from near-freshwater to that of pure seawater – species endemic to these regions have thus evolved special adaptations to tolerate this variability. Brackish waters are home to an incredibly diverse and unique group of animals, many of which are well-suited to be kept in captivity.

Setting up a brackish aquarium

Brackish water aquariums are most often maintained by hobbyists having extensively kept both fresh and saltwater species and wishing to do something more unique and different with their aquariums. More inexperienced hobbyists are likely to stick with what’s comfortable: generally, freshwater aquariums, and undemanding, inexpensive species. In reality, however, the hardiness of brackish water species makes them ideal for beginner and experienced fishkeepers alike, provided they are adequately researched and their needs are satisfied.

The following is an overview of the equipment necessary to set up and maintain a brackish water aquarium:

  • Aquarium: in general, bigger aquariums are easier to maintain, as potential fluctuations in water parameters are mitigated in larger volumes of water. Although brackish water species are more tolerant of variable conditions, it is still best to purchase as large of an aquarium as you can reasonably afford and fit in your home.
  • Filtration: a variety of filtration systems can be used with brackish water aquariums: their suitability varies depending on the species in question. Pufferfish, for example, are messy eaters, and as such require more powerful filtration. Protein skimmers are sometimes recommended for brackish tanks but are generally thought to be unnecessary.
  • Heating: as most brackish species originate from tropical climates, a heater will be necessary. Purchase a thermometer as well and regularly check that the water is at the correct temperature. Ensure the heater is placed such that the heat it produces is efficiently distributed throughout the aquarium.
  • Lighting: if keeping live plants, it is best to invest in a good-quality light unit with a spectrum optimized for plant growth. Otherwise, regular light units are sufficient. LED units are recommended in most cases, as they last for significantly longer than their fluorescent counterparts and consume far less energy.
  • Marine salt: a good-quality marine salt mix is necessary. Do not use table salt or aquarium salt: both are inappropriate for use in brackish aquariums.
  • Hydrometer: the salinity or specific gravity of the water needs to be monitored – a variety of instruments exist to do so. Swing-arm hydrometers are inexpensive and easy to use. Refractometers are more expensive but generally provide more accurate readings.
  • Substrate: the natural habitats of brackish water species are sandy and muddy – in captivity, it is best to recreate these conditions. Play sand is available at most hardware stores and is very inexpensive, but requires very thorough cleaning. Marine aragonite substrates can also be used, and will help buffer the pH slightly.

Brackish species

The following are two brackish water species that are particularly interesting – check them out!

Mudskippers are amphibious fish that live in intertidal habitats and spend a large portion of their time out of water. They use their pectoral and pelvic fins to walk and climb, and breathe while out of water through their skin like amphibians and via a bubble of air they retain in their enlarged gill chambers.

Archerfish prey on terrestrial insects and other small animals by shooting them down with jets of water from their specialized mouths. They are remarkably accurate in their shooting, and can bring down prey up to 3 m above the water surface!