Livebearers, like guppies, platies, mollies and swordtails, are a very popular group of fishes in the hobby. We answer some of the most frequently asked questions about these livebearers to help you get started with these beautiful fish.
What are livebearers?
Most fish lay eggs, but some give birth to live young. There are two different types of livebearers - viviparous and ovoviviparous. In ovoviviparous fishes the eggs hatch internally and are born fully-formed, receiving nutrition from the egg yolk. In viviparous fishes the fry recieve nourishment from the mother.
About 15 of the approximately 480 fish families known exhibit some form of livebearing. This includes half of all sharks and rays, as well as the livebearing tooth-carps, such as guppies, platies, mollies and swordtails, and a number of unusual species.
It is these common aquarium favourites we will be focusing on here, split across two topics, How to keep adult livebearers and breeding related questions.
How to keep livebearers?
The livebearers are often thought to be perfect additions for community tanks for beginners but it does not always go smoothly. Here are some of the common questions regarding keeping these fishes in aquaria.
I've been told that guppies are easy to keep. Why do mine always die?
A decade or two ago, guppies were tough, disease-resistant and easy to keep. Today, things are quite different and they can be hard to keep, disease-prone and sensitive to pollution. Some shops won't stock them any more, and very few recommend them to new fishkeepers.
It's likely that continued inbreeding, the use of hormones and incorrect use of antibiotics have caused genetic and health problems, making many strains much weaker. Sourcing fish from reputable hobby breeders locally or at fish shows like the British Livebearers association can help gain access to fish with better health and genetics! Equally, should you be lucky enough to encounter specimens that are more closely related to wild fish they will likely be stronger and more robust.
Are livebearers best kept in pairs?
Male livebearers can be somewhat over-amorous, so it's less stressful for the females to keep at least two females per male, rather than just a pair. You will of course end up with fry when keeping both genders.
There is the all-male strategy to avoid breeding. Avoid breeding it does, avoid aggression it doesn’t. The competitiveness of males is heightened when denied their female counterparts. In small groups, males will single out the weakest individual and collectively suppress them. You may not notice the bullying as behaviour changes when you approach the tank (when the possibility of food is a distraction).
They aren’t down-right vicious, the domineering behaviour is subtle, like pushing the weakest fish away from food and the odd little peck at the fins from each stronger fish. It may take several weeks for the suppressed fish to show signs of weakness, but once it dies, the next weakest fish is the new target for the remaining group.
This male competition is more of a problem with Guppies, Endler’s guppies and Sailfin mollies but it can be the case with all the livebearers mentioned. The larger the group, the less chance of targeted aggression so keep at least eight males (of the same species) together to help avoid it should you go down the all male route.
What size aquarium do I need for livebearers?
Poor advice is rife when it comes to the size of the aquarium needed to house different livebearers. All too regularly, Endler’s guppies get suggested for nano tanks (45ltrs or less). The males may be small, but they are highly active and competitive fish and, as above, male-only tanks need a good number of individuals to avoid targeted aggression. Mixing sexes? The females are roughly three times the size, and the resulting young will need much more space than a nano tank. Aquariums of around 60cm long or bigger should be used to ensure enough space for subdominant and pregnant fish to retreat and hide.
Swordtails seem to be the least competitive of the livebearers, and the least productive as far as offspring are concerned. This makes them more manageable, but they are a good-sized fish – reaching well over 10cm (in body) when kept well. They are also strong swimmers and good jumpers, so more space is needed than the average 60cm aquarium they are often advised for. Ideally, give them a tank of 100cm or more to really see these fish thrive, you won't be disappointed by the result!
The fins of my guppies keep getting shredded. What's wrong?
Male Guppies have long fins that may be nipped by other fish, particularly by some barbs and tetras. Check the compatibility of any fish before buying them. While fin-nipping is common, shredded fins are sometimes a sign of disease, which is thought to be caused by the ciliate parasite Tetrahymena. Treatment is often difficult, but anti-parasite treatments, especially those containing some copper, can be effective. Adding aquarium salt at a dose of 2-3 g/litre can help reduce salt loss through the open wounds. Good water quality is vital.
Photo by shutterstock
Breeding related questions
It is common for livebearers to produce fry in any community aquarium resulting in much excitement for the owner. So it is no surprise many of the common questions asked about livebearers relate to this!
How do I sex livebearers?
Male livebearers, like guppies, platies, mollies and swordtails, have a modified anal fin called a gonopodium, which is used to internally fertilise the female. Females lack gonopodia and have a triangular anal fin instead, so they're easily sexed.
In some species, such as Phallichthys fairweatheri, the gonopodium may be as much as 50% of the total body length! Whereas, hormone treated female guppies may develop gonopodia. These are useless for breeding and should be avoided.
How do I tell when my livebearers are pregnant?
There are several ways to spot when a livebearer is pregnant, some will be more obvious in particular species. Firstly, the gravid spot: look for a dark spot near the rear the abdomen. This spot becomes more pronounced as the pregnancy progresses and is a good sign that the female fish is carrying eggs. The pregnant female's abdomen will increase in size which will become noticeably larger and rounder compared to non-pregnant females. One other way to tell is that they can show changes to their behaviour. Pregnant fish are likely to hide more often, seeking out secluded areas to prepare for giving birth. Male may also become quite interested in the female as she approaches the end of the gestation period.
Female platies photographed by George Farmer.
How long is the gestation period?
It varies according to species, but most common livebearing tooth-carps can give birth to between 20-200 fry every 4-6 weeks.
Most livebearers reach sexual maturity quickly. Male guppies can breed after two months; females at three months. So the tank can soon become overpopulated if you have lots of females and it is not always easy to rehome the offspring should you have too many!
Related article: 5 freshwater inhabitants that are probably best to avoid breeding
I keep getting fry, but there are no males in my tank. How can this be possible?
Many livebearers produce packets of sperm called spermatozeugmata and impregnate the female with these. Spermatozeugmata can remain in the folds of the ovaries and uterus of female livebearers for up to a year in some species, allowing the female to fertilise several successive batches of eggs from a single spawning.
Chances are, if you buy female livebearers, that they've already been impregnated by any males in the tank, so even if you buy all females you still may become overrun with fry. If you don't want fry, don't keep females.
How do I feed the fry?
Livebearer fry are usually larger than the fry of egg laying species, and are normally able to take fine foods straight away, unlike the fry of egg layers which need to absorb the yolk sac before they will eat. Most newborn fry will take liquid or powdered fry foods for designed livebearers, or live or frozen brine shrimp nauplii. They grow quickly and within a couple of weeks can be weaned on to crumbled flake or growth foods.
Photo by Shutterstock
Should I use a breeding trap?
Most experts agree that breeding traps aren't ideal for livebearers and that they may cause gravid (pregnant) females undue stress. Instead, you can raise a reasonable number of fry in a community tank if you plant heavily with bushy plants like Cabomba, and ensure there are no fish present large enough to eat the fry. For bigger broods you'll need a separate tank to remove offspring into as and when you spot them.
Do you keep livebearers? Why not share your tank over on our Reader's Gallery for your chance to feature your tank and fish in the magazine!