All fish can be overfed and get fat from the excess food. However, when you are trying to breed fish, you need to feed them more often so they can build up reserves including eggs and sperm. If the fish are hungry and not getting much food to eat, they will be less inclined to breed and any babies they produce will not be very good quality.
If fish are fed well for a couple of weeks before breeding, they usually produce more young and the babies will be healthier.
So for general maintenance of adult fish that are not breeding, you only feed a little bit once a day.
For fish that are going to be bred, you feed 3-4 times per day (or more often if you like) so they can get bigger and fatter and produce more eggs.
If fish are fed well for a couple of weeks before breeding, they usually produce more young and the babies will be healthier.
So for general maintenance of adult fish that are not breeding, you only feed a little bit once a day.
For fish that are going to be bred, you feed 3-4 times per day (or more often if you like) so they can get bigger and fatter and produce more eggs.