Thanks Fishguy,
yesterday I got a mix of shrimp and crustaceans for turtles suggested by a shopkeeper, promising I'd get the money back if it doesn't work. They're clearly not crazy about it, but they do eat it on the long run, when nothing else is given. So for this time I'll keep going with this. Next time I'll try to get something more palatable, possibly Ikari. I see also Sera has dried food for carnivores.
At the moment the only thing they really love is frozen bloodworms, which is just devoured in a matter of seconds. Daphnie don't make them particularly happy, and lots of them are eventually missed, polluting the water.
Any other fresh/dried food anyone would recommend with these fishes based on direct experience? I'd love to give them a varied diet. Obviously, ASAP I'll treat them with live insects when possible.