Q&A: Whats an easy fish to breed in a 10/20gallon tank?

All livebearers. You need 2 females to 1 male, (2:1) for livebearers. They breed easily. If you want more of a challenge that might sell for a little more, then a betta or a kribensis cichlid. Kribs will form monogamous lifetime partnerships and will not like to mate with others. Bettas will breed with any betta but sometimes the pairing doesn’t work. It’s a hit or miss. Out of bettas and Kribs, Kribs are easier as they take care of their own fry and don’t need as much work as bettas.

livebearers (guppies,platies,mollies etc etc

heres a link on them

http://www.google.com/imgres?imgurl=http://farm4.static.flickr.com/3065/2612783820_7ffa4b4f1c_m.jpg&imgrefurl=http://fiveprime.org/hivemind/Tags/cichlid,orange&usg=__rZuhKp7kjVa1zd-_OedGXUKNSXw=&h=179&w=240&sz=16&hl=en&start=147&sig2=90anlwfqL34cWN9RPabfZg&zoom=1&tbnid=ukk_1icZrjsNvM:&tbnh=127&tbnw=175&ei=6KFxTOfTOsGclge_yejRDQ&prev=/images%3Fq%3Dpink%2Bconvict%2Bcichlid%26um%3D1%26hl%3Den%26sa%3DG%26rlz%3D1C1_____enUS384US384%26biw%3D1280%26bih%3D697%26tbs%3Disch:10,3279&um=1&itbs=1&iact=rc&dur=454&oei=s6FxTI-5JIH_8Aal7oTyCg&esq=7&page=7&ndsp=24&ved=1t:429,r:2,s:147&tx=132&ty=42&biw=1280&bih=697

click on one of the pictures of fish on the bottom to learn about them.

Convicts or Jack Demsey’s are among the easiest fish to breed. As long as you have a pair of either species you will have babies. Both are great parents, guard their young well, become aggressive with their young and mate but both will breed to the point of exhaustion and over population which can cause toxic buildup causing illness and death in the fish. For example, one month you have one pair of Jack’s or Convicts and plenty of room. A few months latter you have several pairs of fish mating, most fighting over their space, their young growing and mating creating toxic waters. I used to breed both species. I had two 75 gallon tanks. I started with two pairs of each planning on selling the babies off to make a few extra dollars. Five months latter when I had more fish then I did sales I had to buy more tanks to separate the fish costing me more money then I planned to spend. So if you go with either of these be ready for allot of extras not being sold.

All live bearers such as ~ guppies, mollies and platys are easy to breed
the guppies and platies would be the best for you because of there size.
be careful guppies can have a large number of fry ( baby fish when first born) and breed rapidly. the platies are the same way but are a little less sexual as the guppies.
~edited~
Lord Galvatron is right and yes the mother and all other fish will make a snack out of the fry.