Guppies sometimes fight among themselves or with other fish in the tank.
Guppies are an attractive, easy-to-keep tropical fish that can be a colorful addition to your aquarium. They can get a bit territorial, though, and when that happens your peaceful little guppies may end up taking bites out of each other’s fins and tails, or perhaps fighting with your other fish.
Watch your guppies carefully when you add new fish to the tank. This is a time when fighting is likely to occur, and your guppies may attack the new fish by nipping at their fins and tails. Guppies will sometimes attack other guppies, especially those of the same sex, and they may also attack larger, slow-swimming fish with trailing fins and long tails, such as mollies.
Look for signs of fighting, particularly damaged or frayed fins and tails. In some cases, fish that are picked on may hide in your tank and you won’t see them very often. You may also discover a dead fish that seems to have died for no apparent reason. Look closely to see if his fins and tail show signs of damage. If so, the fish in your tank are fighting.
Separate any fish that you suspect of fighting. If you have only guppies, you may not need to remove any, as fighting among them, especially the males, is typically more for show than anything else. Make sure that your fish are not overcrowded, and provide plenty of hiding spots so that any fish that is being chased by an aggressive guppy has a place to hide. Plants that float on the surface of the water are especially helpful as a hiding place for guppies, since they tend to rest near the top of the tank.
Check if other fish in the aquarium are attacking your guppies. Species with long, flowing fins and tails may see the guppies as rivals and fight with them, and bettas and gouramis can quickly kill guppies if they decide to attack them. Small, fast fish, particularly some members of the tetra family, may nip your guppies’ fins, causing the guppies to look ragged even though they aren’t the ones doing the fighting. Careful observation is the best way to find out what’s going on in your aquarium. You may need to remove the offenders.