I have four tiger barbs in my new aquarium and was wondering about a tiger barbs diet requirements. Can tiger barbs eat insects like small black ants or red ants?
According to FishBase, tiger barbs (Puntigrus tetrazona) are omnivores that eat "worms, small crustaceans and plant matter." It doesn't look like FishBase has a whole ton of food item data for them yet, but a quick Google search mostly gives results that describe them as omnivores as well. So in the wild they probably wouldn't turn down the random ant that falls into the water.
But I would not recommend collecting wild ants and feeding them to your fish. For one, you might not be putting down ant traps, but you have no idea where else the ant colony has been foraging -- a large colony will have a pretty wide range, and they could easily find something that's toxic to fish. Ants greet each other by sharing food, by the way, so slow-acting toxins or ones that are not directly toxic to ants will spread across the whole colony eventually.
Second, ants themselves are often toxic: many species defend themselves with formic acid, alkaloids, and other substances that are, at best, extremely foul tasting to predators. So although the barbs may instinctively grab for one, they might not actually eat them. And depending on the species, the barbs might even be harmed by this.
It's a great idea to vary their diet though. I'd recommend supplementing their daily staple food with something like freeze-dried brine shrimp, which are safe and not too unlike the freshwater crustaceans the barbs would hunt in the wild. And I'd also look into some plant matter -- many fish will actually eat fresh or steamed vegetables, like peas or spinach. I'd do some web searching to see what other people's tiger barbs enjoy.