Guest Author - Jilly Florio

There seems to be some confusion on what brackish really is. In nature, it's a place where sea water and fresh water mix, like an estuary. So a true brackish tank has to be as carefully monitored as a marine tank, because you have to walk that line between having too much salt and not enough. Also, there are different levels of marine and fresh mixing at each place in nature, so some brackish fish are high brackish, and some are low brackish.

Then there are the fish that can adapt to almost any conditions. The livebearers are in this category. All fresh water has SOME sodium in it, so that's why adding aquarium salt does not make your tank brackish. Livebearers like some sodium but are adaptable enough to not notice. Here I am talking about guppies, platies, mollies and swordtails. I don't know how endler's or goodeids are with regards to salt, so I can't comment.

Mollies are one fish that you can even keep in a full-strength marine tank, once you acclimate them. Some ciclids can tolerate full-marine levels as well, like the severum and chromids.

There are also some fish that use different parts of the estuary at different life points: no one keeps salmon fish, but they are a good exampe, swimming up to fresh water to spawn. Wild scat fishes spend their juvenile time in fresh and slowly travel down to the marine environment as they get older. So there are some juveniles in a brackish system that I care for, and one client has adult scats in marine tanks.

Brackish systems are not for new fish keepers, since they are harder to get right than freshwater tanks. Even simple marine tanks, with damsels and clownfish, are much easier. Most true brackish systems require mixing fresh water with marine mixtures, checking the specific gravity, and topping off appropriately.

Once you've gotten your feet wet (or, salty, rather), with those kinds of tanks, then putting together a brackish tank is a great goal.

Related Articles:
The Livebearers : Guppies, Platys, Swordtails and Mollies
Your First Marine Tank

This interesting book is a good place to get started on designing your brackish, fresh or marine ecosytem right!
Setting Up Dynamic Aquariums