small cooked prawns, bloodworm pellets, live earthworms, earthworm sticks, hikari tropical sinking carnivore pellets, krill, chopped mussells, brineshrimp pellets....the list is extensive!
Edit: Cat-e-log also lists an incident of the stomach contents where there was a lots of seeds of waterside plants. if you were inclined you might want to try sunflower seeds, pumpkin seeds etc - maybe you might also consider trying soft fruits which are known to be consumed by some of the bigger pims in the wild - like plums, peach etc