Are Molly Fish Aggressive?

One of the questions that seemed to pop up more frequently is if molly fish are aggressive? This article is a compilation on researches about molly fish nature.

So, are Molly fish truly an aggressive species? Just like many fish behave in an unpleasant situation, mollies are not exempted. However, mollies are not very aggressive, when compared with some species like male betta. Although, they protect themselves against invaders.

Mollies are one of the most exotic and beautiful species that exist as live bearers. However, with these beautiful qualities they possess, they may be difficult to due to certain reasons.

True Nature of Molly Fish

These fish are a native habitat that extends from the Southern United States to Mexico. Moreover, they best thrive well in brackish estuaries. Also, this is why you must make inquiries about your fish before setting up an aquarium for it.

Sometimes, introducing molly fish into a tank maybe a handful. Also, with no proper knowledge as regards its tank requirement, in terms of size, and clean up. There is a high chance the Molly fish will show off its aggressive trait often.

Moreover, you should note that mollies often prefer to stay in a place of plenty warmth and the least temperature of 78 degrees Fahrenheit.

What to Do About an Aggressive Molly

 Often when a molly fish appears unhealthy, there are several factors that contributes to this, with unkempt aquarium environment being the most prominent.

Moreover, to endeavor your fish have a long lifespan, there are certain hygiene rules you must keep to, and requirements to meet.

Amidst this, there may be unlucky days when a molly fish sustains his aggressive nature for a long period. What then needs to be done?

A molly fish remains non-aggressive if the following measures are observed;

  • Water Quality: Mollies are not handy to keep when it comes to water quality requirements. However, adding sea salt to one teaspoon per gallon gives a more positive effect.
  • Live Plants: Keeping molly fish is less stressful when the fish tank has proper lighting with plenty live plants. In most cases, they nibble at these live plants. Also, it is good to keep some algae in the tank, as they like to graze new algae growth.
  • Feeding: Mollies usually feed on algae growth in an aquarium. Also, they enjoy nibbling at it. However, you can provide an alternative to the fish tank, if it lacks algae. Moreover, some of these alternatives include chopped boiled spinach in small quantity, special commercial molly food, spirulina flakes, and several others.

Moreover, sailfin mollies are one of the most dramatic livebearers that exist. Sometimes, they can be more difficult to maintain compare to other molly fish. However, sailfin mollies require a 20gallon long tank to swim around. Moreover, any restriction on their movement may diminish their health.

Tips in Keeping Fry Safe from an Aggressive Molly Fish

  • Separate pregnant mollies in a community tank and place it back after she gives birth.
  • Ensure you put the large live plants in the tank, to serve as hiding ways.
  • You can also get a separate breeding box for your mollies.
  • Ensure to keep the fry safe in a separate tank, until you are sure they can stand the adult mollies. However, to be certain of this, a molly fry should be larger than the mouth of adult mollies, for survival.

More importantly, to prevent your molly fish from expressing an aggressive trait towards each other, it is important to be able to differentiate each sex. Moreover, to prevent casualties from happening by separating them, here are some ways to differentiate male from female gender;

  • Male mollies have pointed gonopodia
  • Females have a wider anal side for breeding
  • Males have vibrant and brighter color than females
  • Female mollies have short fins with triangular-shaped anal fins, while the males have larger fins.
  • Male mollies are torpedo-shaped, while female mollies are bulkier.

Related Questions

There are other related questions that many people have always seem to inquire answers for, concerning molly fish. Some of these questions include;

Can Mollies Live In a Community Tank?

When mollies are put in a community tank, they often become sick, and some may even die early. Also, Mollies are the most delicate species among live bearer. Such that, they mostly develop an ailment known as “shimmies”, even within a short period of exposure to a stressful environment.

Nevertheless, this is merely a symptom, that most fish express when they are in a stressful environment. Thus, it cannot be fully categorized as a disease.

As stated earlier, Mollies are semi-aggressive, they only protect themselves when danger arises. Moreover, just as humans, it’s a way of a survivor – the ability to thrive.

Can Molly Fish Be Aggressive to Each Other?

This question cannot be generalized. Mollies are beautiful creatures, and thus must be treated as such.

However, there are cases where you want to watch out for the species or type of molly you are putting together in the same tank. For example, it will be a bad idea to keep a tank acclimated aquarium fish or store-bought fish with wild fish.

Wild fish are more exposed to dangerous infections and as such, diseases or parasites can be infected into your home aquarium. Moreover, they are usually more aggressive.

What Happens When Mollies Are Chasing Each Other in A Tank?

There are several reasons why mollies chase each other in a tank. As a responsible aquarist, it’s ok to worry about them chasing and nibbling at each other. However, this may be an act of fun. But there are exemptions where an aquarist has to be observant and place the mollies in separate tanks.

1. Mollies Sex: The most predominant reason for mollies chasing each other is seen when they are of the opposite sex. Moreover, the male chases the female around for mating.

However, it is advisable not to place opposite sex in the same tank, as the male counterpart tends to be more aggressive. Unless the purpose of raising them is to breed them together.

Also, a male molly may chase after another male, in trying to gain his territory by chasing off invaders or to catch the attention of another female present in the aquarium.

2. Mollies Fry: Mollies do not lay eggs, I.e. they are livebearers. Unfortunately, adult mollies lack parental morals and are aggressive towards their Juvenile.

However, they chase them around the tank, with the aim of feeding on their fry. Also, in worst scenarios, parent mollies are seen feeding on their own fry. Sometimes, for some over-aggressive mollies, this unpleasant situation may be difficult to control.


Aggression is a common trait in many fish. However, it can be managed if the fish keeper follows the tips started earlier. If after trying out the tips, you observe no positive change, then the molly must be an extremely aggressive one. To ensure the safety of other fish, it is good if you remove the aggressive molly from the community tank. Moreover, good luck and success with your fish keeping. Also, we will be glad if the processes yield you a positive result.