Brackish water aquarium fish

All of the rivers of the world ultimately contribute their water to the sea. In this region there are extremes of salinity, temperature, and biological tolerance. Fish that live in this zone are called “brackish” to reflect their tolerance of a wide range of salinities. Many faimiles of fishes episodically inhabit this region. Sharks are occasionally found up to 1000 miles up the Mississippi River, and many fresh water fishes can be seen miles out to sea. These are the exception.

There are many families of fishes in a fish store, but five families are recognized as be truly brackish, with many other families tolerant of the varying salt concentration.

The changing biological conditions of the brackish environment requires frequent feedings to fuel the fishes high metabolism. So lets look at four of these voracious families!


The Monos come from the coast of Africa and Indo Pacific. They are extremely fast predators that thrive on a diet of worms, shrimp, and other high portion foods.

They will only bother fish and inverts that they can eat, and may act aggressive to smaller kin. If the salinity is too low they are prone to “Ich” so avoid pure fresh water.

As with the other families, at least 1 tablespoon of non iodinized salt for every 5 gallons is an absolute minimum.


The are four species of Archer fishes. Spitting at small insects that live up to 3 feet above the water line, they can actually dislodge a tasty morsel!

Greedily consumed are small insects placed at the water’s surface, however they will adapt to a variety of prepared food. Insure that their food floats, as the are poorly equipped to feed on food that is not on the surface.

Their eyes can compensate for the refraction of light through the air water interface. After adjuting to the aquarium they will actively spit at a small “fake bug” hung over an open aquarium if this spitting is followed by feeding!


The spadefish and batfish include over 14 species, and most are very hardy with the exception of the Pinnatus Bat (Platax pinnatus). They will eat almost anything, and grow quickly.

You should look closely for signs of aggression and note that they are especially prone to “Ich.”

Larger specimens may scratch themselves on coral, so keep the tank spacious and the decoration sparse. A finicky feeder can be tempted with live brine shrimp and try to insure that they can eat their fill.


The three species of Scats belong to a family of fishes that literally translated means “dung eaters”. So it is obvious that they will eat anything, and lots of it!

Their dorsal spine is mildly venomous, so watch out. They have extremely high metabolisms, so the old adage ” a fat scat is a healthy scat” really applies.

Scathophagus argus is actually both the Green and Ruby Scat because it occurs in two color varieties. They can be a bit nippy so watch out for signs of aggression towards timid cohabitants.

Brackish water in a nutshell means a high metabolism. Insure an ample diet and compatible tankmates and a clean aqaurium and these will thrive. A little bit of care and food goes a long way!

AUTHOR: Jim Wolf, Marine Biologist