Mosquitofish (I have them in my 75 gallon reef just fine)
Tank Size
20 Gallon for adults, at least 10 for juveniles
Temperature
Mosquitofish are commonly kept in ponds, so a temperature of 60-85 would be acceptable
Adult Size
About 3", the biggest I've had is about 2.5"
Temperament
Peaceful, generally stays away from the other fish
Reef Compatible
Yes, they generally stay away from the other fish, and invertebrates. They do not interact with corals in my experience.
Diet
In my experience they eat anything that their tankmates will eat: mysis, flakes, pellets, and pretty much anything else.
Origin
Mississippi River, down to the gulf, and also found in Northern Mexico. They are found in full FW, all the way up to full SW (I got mine to SW through drip acclimating for 8 hours)