If the fish is new to its environment it may need more time to settle down. If not then there will be something wrong with its environment. The most common problem is bad or poor water conditions. If this is the case, then replace all the water or at least most of it.
Fighting Fish do eat each other so, yes
No fighting fish eat when ever they get the chance.
No
No. The "fighting fish" ie Betta, will only fight members of his own species. Oscars will eat Bettas.
they eat small animals and frogs and fish
Fish
The developing fish inside the eggs eat the eggs.
Any fish-eating fish large enough to eat one is a predator.
Yes, if the ants can actually go into the fish tank.
fish pickles
Yes.
Fish, crustaceans, and cannibalisums.