If they really are RTBS, then grow them on and sell them; I honestly doubt it though; RTBS don't breed in tanks; they spawn them in the Far East with hormone injections.
I suspect they're livebearer fry of some kind; probably Endler's by the sounds of the colours, but could be any one of them (guppies/mollies/swordtails/platies)
There's so little nutrition in cucumber, it's hardly worth feeding it. Try; sweet potato, carrot, peas (all these need to be lightly cooked and the peas shelled), mango, apple, courgette, scalded lettuce, tomato (end slice with no seeds).