Which a 29 gallon tank, your fish variety is a moderate size. There is a rule, the rule of thumb. It means 1 inch of fish per gallon. Some fish however are more territorial or aggressive and require more room such as the dwarf puffer. Other fish are best kept in a tank of the same species. I think with a 29 gallon tank it depends on your experience. If you are a beginner, you could try guppies, mollies, swordtails, platys, tetras, or other small simple fish. If you have exerience with some fish you could try chichlids, gouramis, angelfish, dwarf puffers (they are small but need 5gallons each). If you are going to decide on a fish, I highly recommend you research your fish and find out all its necessities. Also try cycling your tank 3-4 weeks and then get a small fish or two such as a guppy. Then if they are doing okay, you can add your fish of choice. Make sure you know if your fish likes
"hiding places" because some fish will become stressed and very territorial. Good Luck and I hope this helps you! Also if you are going to add the biggest fish, I would try a large freshwater puffer which needs around 30 gallons.