Brackish aquarium fish

Brackish fish live where fresh and salt water meet, from mollies to figure-eight puffers and monos. Each profile lists the tank size and conditions a fish needs, so you can match a species to a brackish tank.

Tank size: 5–225 gal; 5 gal (20 L) to 225 gal (850 L); half the list needs 32 gal (120 L) or more
Temperature: 73–82°F; 23–28°C, most of the list
pH: 7.0–8.0; Most of the list
Difficulty: 9 easy; 17 medium · 23 difficult
Temperament: 18 peaceful; 25 mostly peaceful · 6 aggressive

49 species and 18 varieties

What brackish actually means

Brackish water is fresh water with a measured amount of marine salt mix, the conditions of estuaries and mangrove creeks. It is its own middle path: more setup thought than freshwater, none of the reef equipment of a marine tank. A surprising number of familiar shop fish are estuary fish at heart; mollies and guppies both tolerate brackish conditions happily.

Good first brackish fish

Livebearers are the easy way in: mollies genuinely thrive with salt in the water, and Endler's livebearers, guppies and least killifish handle light brackish in tanks as small as 5 to 15 gallons (20 to 55 liters). The figure eight puffer is the classic brackish character fish, a personable 3 inch (8 cm) puffer for a 20 gallon (75 liter) tank.

Many brackish fish grow toward the sea

A lot of brackish species are sold small and end up large, schooling and nearly marine. Scats and monos want around 105 to 120 gallons (400 to 450 liters) as adults at increasing salinity; a banded archerfish grows to 12 inches (30 cm); the Colombian shark catfish sold in freshwater tanks is really a 14 inch (35 cm) brackish fish that needs over 220 gallons (850 liters). Check the adult size and tank size on the profile before committing.