Why Are My Black Molly Fish Attacking Guppies And Killing Them?

Mollies can live with guppies peacefully cause both are tropical freshwater fish and have similar feeding needs. They can be friendly with each other and will rarely attack each other. However, sometimes mollies may show aggressiveness to guppies, and it is to defend their mate or if they think their fry is at any risk from other fish. 

Some Reasons Your Black Mollies Are Attacking Guppies

When there is not enough food in the tank for all the fishes. This is also the time when your molly may compete with your guppies, to the point of killing them for food.

You should ensure that there is enough food to go around and maintaining the right amount of food ensures you will have a tank with a peaceful environment. 

When there is not enough space. Another reason that your molly may become aggressive with guppies is when the space is insufficient for all the fish to move pleasantly.

This is the time when the larger molly may kill the guppies. The molly may get hostile to the guppies, as there are no spaces to dart in and out.

Those who take care of both species should understand that they need enough space where the fishes can move around and hide on decor that is inside the tank.

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If the tank is just too small for them to move around, the molly can become aggressive and this is what you should prevent from happening. 

Interbreeding. There is a chance for mollies and guppies to interbreed, and when male guppies pester the female molly, there is a tendency for the female molly to fight back and hurt the male guppy. The molly can even wound the guppy fatally or kill them. 

Female mollies can be temperamental, and when they chase the guppies, they can start nipping at their fins and hurt them in the process. 

Crowded Tank Can Make Mollies More Aggressive

When mollies and guppies start to give birth, there is a chance that your tank can become too crowded. It is a start for both breeds to get affected because of the competition in the space and food.

Mollies will tend to protect their fry, and when there are bigger mollies compared to guppies, then mollies can easily hurt and kill the other breed. 

When you know your fishes are about to give birth, make sure that they are separated, and when the molly or guppy gave birth, ensure that you separate them from the other fishes and before they drop their fry. This is the best way you can prevent any aggressive behavior from arising in the tank as well. 

Molly fish can get aggressive in defense of their mate or to eliminate competition.

Mollies can hurt a guppy just because they are competition to them. When a molly is mating with another, and they see other fishes entering their territory, the molly can get aggressive to protect its mate. 

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Stressed Out Molly Fish Are More Likely To Attack

Mollies and guppies can get stressed because of the water environment. Molly can become aggressive and may start hurting the guppies.

Make sure that you are regulating the temperature in the tank. It should have the right temperature, which is not too hot nor cold since both fish are freshwater tropical fish. Watch the right temperature of the water by checking on it now and then.

The sudden temperature change can make the mollies or even guppies stressed and hostile. 

Incorrect oxygen level can also be an issue. This is also another reason that your molly may attack your guppy that even if they are peace-loving fish, the fluctuating oxygen level in the tank may be the reason. Add lots of plants to improve the oxygen level and help keep the tank clean.

This is also a preventive way for your molly to see the guppies. The guppies have a place to hide, and they can stay safely hidden and not get attacked by any mollies, for that matter. 

When There Are Smaller And Weaker Guppies To Attack or Bully

Mollies, when they find their target, can become mean and aggressive. When they see a guppy that is weak and slow, they tend to harass the poor guppy. They chase the guppy and nip on their fins to the point of fatally hurting the guppy. 

When the condition in the tank is not perfect, there is a chance for other fish to get weak and sickly, and this is what mollies can target. Ensure that there is clean water, the correct oxygen level, and perfect water temperature to prevent such from happening. 

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When there is not enough food. The big and colorful fin can be good food for mollies when there is not enough to feed them. They can become hungry and may start catching other slow-moving fish to serve their hunger. When some guppies are slow, and they have colorful fins, they can become the target of hungry mollies. 

Mollies Have An Aggressive Temperament By Nature

Some mollies may not have a peaceful temperament and can start harassing other fishes, even their kind. Small guppies can become their victim just because they can bully these small-sized fish.

When mollies are fast-moving, and guppies move slowly at times, there is a big chance that they can become a target for mollies, who are bullies. 

When you see your molly doing this to other fish in the tank, you should separate said molly and put them in another tank where there is no room for them to hurt other fishes. 

Both can live in the same tank peacefully as long as it is in the right environment. Their water and food requirements must be met, and their population you should control. When there is too much fish inside the tank, this is when the problem starts, and it is the same when there is not enough food to fill these fishes. 

Guppies and mollies can beautify your tank, and they can live together peacefully if you give them everything they need and care for them the right way. It ensures you of friendly tank mates for a longer period.