The rule is 1 inch for 1 gallon of water. the product page ses its 16 gallon so you could have four fish that would mature to about 4 inches with no problems. for what kind, do a lot of research and be sure the fish you choose do well with each other. Example, you couldn't have 4 bettas because they would kill each other, even the girls might and would need close monitoring.
Size, temperament, environment such as needed temperatures to thrive all need to be researched. I put 4 Gourami's in my 50 gallon with the neons and they chased them unmercifully.
its not a simply answered question. do lots of research :D
Top 100 Contributor
answered 2 years, 6 months ago
4out of 5found this answer helpful.