With their bright colors, vibrant patterns, and livebearing habit, Mollies are among the most popular fish in the hobby.
Mollies are usually displayed in large groups in pet stores, so many beginners assume that these are schooling fish.
But is that so?
Well, Mollies are actually not schooling fish, although they do like to shoal! That’s a small but important difference.
Confused?
Read this guide to learn more!
Schooling Fish vs. Shoaling Fish
There are subtle differences between the fish behaviors of schooling and shoaling species.
Schooling Fish
Safety In Numbers
Schooling fish swim in tight formations to protect the school from predators. The fish’s behavior is closely coordinated, with the whole school changing direction simultaneously, leaving no fish exposed to attack.
Simply put, predators find it much easier to grab a solitary fish than trying to select one from a large group.
In addition, the sight and reflection of a large ball of fish swimming together can confuse potential predators, giving the fish a chance to escape or hide.
Territory Defense
In addition, fish are better equipped to defend their territory in a large school. Semi-aggressive bullies are far less likely to take on a massive group than one or two individuals.
Easier Swimming
It’s also thought that schooling in tightly packed groups reduces friction, enabling the fish to save energy and swim more efficiently.
Finding food is considerably easier in a large group, as more sets of eyes are on the lookout for a snack.
More Efficient Spawning
Finally, during the spawning season, swimming in a school means that at least some of the fertilized eggs and fry will survive simply because of the huge numbers produced by a large school of fish.
Why Don’t Schooling Fish Collide?
Schooling fish have evolved complex senses that enable them to move smoothly as a group without crashing into each other.
So, how do the fish do that?
It was once thought that the school followed one leader. However, that theory has been disproved, and it’s now known that every fish follows the movements of its companions.
Pheromones also come into play, helping the fish instantly sense their schoolmates’ movements and follow them.
Schooling fish species have their eyes on the sides of their head, enabling them to easily see what’s happening next to them and react accordingly. The fish also use their hearing, sight, senses of smell, and lateral line to plot a safe course within the school.
How Many Schooling Species Are There?
Roughly 25% of the world’s fish species are known to school throughout their lives. Smaller, peaceful fish generally school more than larger species, largely for safety in numbers.
That said, Piranhas live in massive schools, sometimes eating their smaller, weaker companions, even family members!
How Many Fish Are in a School?
In the wild environment, fish schools are generally pretty large, often with hundreds or even thousands of individuals in the group.
In captivity, schooling fish must have at least six members in their group to be comfortable and confident. That said, you can never have too many schooling fish in the school, provided you don’t overcrowd your tank.
Schooling fish you often see in home aquariums include loaches, danios, and barbs.
Shoaling Fish
In contrast to the disciplined, regimented habits of schooling fish, shoalers gather in loose clusters, which can be a mixture of different species.
Shoals are typically made up of fish of different sizes and species that gather randomly near a valuable resource, such as spawning grounds or food.
A shoal gathers largely for social reasons. In essence, shoaling fish prefer to live in the company of others, usually for reasons of safety. Within the group, the fish act as individuals rather than as one unit, which is what you see in schools.
How Many Mollies Should Live Together?
So, how many Mollies should you keep together?
To some extent, that depends on the species of Molly you want to keep. Some Molly varieties, such as Sailfin mollies, prefer to live in large shoals of six or more, whereas Shortfin mollies are happy with just a couple of companions.
As with any fish species you’re thinking of keeping, you should thoroughly research the Molly type you’re considering taking home. If you’re unsure, we recommend you keep larger numbers of Mollies than fewer.
Male-to-Female Ratio
You can keep all female fish together without problems or keep a mixed shoal with just one male Molly to every three or four females. That helps to prevent aggression among the males and stops them from harassing the females too much.
Did you know that female Mollies can carry fertilized eggs inside their bodies and can give birth to live young without even having to mate? So, even if you don’t have male Mollies in your tank, you can still increase the population!
Stress!
Mollies keep their eggs inside their bodies until they hatch into live fry and the female gives birth. That process is extremely stressful for the fish. In fact, some female Mollies die immediately after giving birth due to the stress of the whole process.
The courtship process is also extremely stressful, with male Mollies continuing to pester and harass females even though the girls are already pregnant.
So, if you have too many males in relation to females, you can see that stress levels in your tank will quickly go through the roof!
Can Mollies Live Alone?
Shoaling fish are social animals that do best when kept in a tank with others of their own species. For that reason, we don’t recommend keeping one Molly alone.
If you keep a fish alone that’s evolved to live in a shoal or school, the fish will become stressed. Stress and loneliness will impact the fish’s immune system, leaving it open to attacks by common fish diseases and parasites and undoubtedly shortening the creature’s lifespan.
Final Thoughts
I hope you enjoyed our guide to whether Mollies are schooling fish. If you found the information helpful, please take a moment to share the article.
Contrary to popular belief, schooling is not the same as shoaling, and now you know the difference! Mollies are shoaling fish, living in loose groups that swim together while individuals remain independent of each other within that social group.
Mollies are happiest when kept in groups, although it’s important to keep the ratio of males to females correct to prevent the female fish from being hassled too much by amorous males. We recommend keeping three female Mollies to one male.
How many Molly fish do you have in your setup? Do they shoal with tank mates of different species? Tell us in the comments box below.
