Guppies and Mollies

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Guppies & Mollies are both closely related, belonging to the Poeciliidae family, and are some of the best-known fish in the aquarium trade. Despite still being recommended as good beginners fish, there are health issues that have become apparent in recent years, which have resulted in a necessary change in correct advice regarding the care of these fish.

Male red orange Guppy

In this article, we will take a look at the guppy Poecilia reticulata, the Mexican, or Green Sailfin Molly P. velifera, the Black, or Short-finned Molly P. sphenops, and the Sailfin Molly P. latipinna

In the wild

The Guppies natural habitats range from South America (north of the Amazon) to Mexico and Florida. Throughout this distribution they can be found in varied waterways and isolated areas. The guppy has also been artificially introduced all over the world, especially in Asia, where varieties escape from large breeding facilities. There are even documented reports of guppy populations in the UK, centred around warm water factory outlets. In some areas, the Guppy has been introduced in order to eat mosquito larvae and keep mosquito populations down.

The molly has a similar natural distribution and can be found mainly in Central America and Mexico as well as brackish and coastal regions. Whilst the wild molly has the same basic body shape as its captive bred cousins, the wild guppy is significantly different in appearance to the varieties seen in shops today. Wild guppies are much smaller, and whilst wild males are still colourful, with just a few bright spots on a plain body and no long fins, they look entirely different to their fancy tank bred counterparts.

The results of breeding

Virtually all guppies and mollies seen for sale today are varieties that have been bred for the bright colours and attractive fins. Inevitably, this has resulted in some health problems as repeated breeding within a limited gene pool damages the fish's natural immune system.

The effect is much more noticeable on the guppy, partly because of its initial reputation for being a hardy beginners fish. Whilst 10 years ago this may have been true, the majority of guppies on sale today are quite delicate fish, which will easily succumb to disease problems and early deaths. It can no longer be said that the guppy is a hardy fish suitable for beginners, and they should now only be purchased for well-established aquariums with good water conditions.

The molly in contrast, is still a relatively tough fish, but only providing it is kept with some quite specific guidelines. Tank bred mollies are very prone to skin based problems such as velvet disease, fungus, and whitespot, and are easily stressed by fluctuations in water temperature. A very effective way of boosting the mollies natural defence to these problems is to add a little aquarium salt to the water, which both reduces stress on the fishes body, allowing more energy to be used for the immune system, and also creates unfavourable conditions for disease pathogens. The application of salt will also benefit guppies in the same way, but is not as essential.

Aquarium conditions

Both guppies and mollies require similar water conditions and generally do best in moderate to hard water with a neutral or higher pH. A stable temperature is very important and warmer water around 25-28C (77-82F) tends to provide the best conditions.

Do not fall for the advice of inexperienced retailers, which may happily sell both these fish for unheated tanks. Although more hardy strains and wild varieties of these fish will quite happily live in cooler or fluctuating temperatures, much of the stock on sale today will not. Many fish keepers do keep these fish in cool water, and you may even know of someone who has done this with no problems, but this is very much a case of 'luck of the draw' and is not a risk we should put our fish through.

The size of the aquarium should depend on the eventual size of the fish. For guppies, which will reach only 3cm (males) and 5cm (females), and black, or short-finned mollies (6cm), a 60cm aquarium will be ample, whilst sailfin (12cm) and mexican sailfin mollies (18cm) will require a minimum of 90cm.

Aquarium decor is not overly important but some planted areas and darker hiding spots are preferable. Both these fish are surface dwellers and although they will spend most of their time out in the open searching for food, a little surface cover will be appreciated.

Mollies are natural grazers, and a good varied died including some vegetable matter will improve health. Good foods include herbivorous flake, algae wafers, spirulina enriched foods, and raw foods such as cucumber.

Sex on the brain

Guppies and mollies do not carry out brood care like more robust fishes such as the cichlids, and instead opt for the 'as many young as possible' method of reproduction. In fact, if the males are not looking for food, they will be looking for a female to mate with.

In the enclosed environment of the aquarium, this constant search for a good time can take its toll on the female population, and for guppies, if you choose to have both males and females, you should make sure you have twice as many females as males so that the females are not constantly harassed. Male mollies are equally always on the search but the more robust female molly can quite easily put the males in their place, allowing mollies to be kept in pairs without difficulty.

Both these fish are livebearers, giving birth to live fry rather than eggs. To achieve this the females must be fertilised internally, and this is carried out with the help of the males modified anal fin, called a 'gonopodium', which is used to transfer milt into the female.

Male guppies can mate at only 2 months of age, whilst females can produce young at 3 months, and between 20-200 young are produced in one batch, of which the female can have several batches from one mating. The duration from mating to birth varies depending on environmental conditions but is usually around four weeks.

With production of young at a maximum potential of 200 young every month, it is no surprise that the guppies other common name is 'millions fish'. Mollies have a slightly longer period between mating and birth, and produce between 20-60 young per batch, although the mexican, or green sailfin molly P. velifera can produce up to 200 young.

Breeding in the aquarium

Providing you have a male and female, these fish will need no encouragement to breed in any aquarium. In many cases, the young go unnoticed as other fish in the aquarium, and even the parents usually eat them before they are spotted.

If you wish to raise the young successfully, the best option would be to set up a separate small aquarium into which the pregnant female can be placed to give birth. If you cannot afford, or do not have the space to do this, the next best option is a large breeding trap which can be floated in the main aquarium. The fry-rearing tank should be well planted and filtered by a small air driven filter, which will not be powerful enough to suck up the young.

Simply letting the fish do their thing and raising the young is relatively straight-forward, but you will find that the young fry may begin to show less intense colour as they revert back towards their wild forms. Breeding these fish to retain a strain is a much more complicated affair and involves careful selection of parents, and timely separation of individuals.

Tank mates

Mollies can reach a good size and will be able to cope with more robust and active tank mates quite well, but aggressive species should be avoided. Tank mates for guppies are a little more difficult to select and small, peaceful fish are the best option. The extensive fins of the male guppy are an irresistible target for fish with a tendency to fin nip, and many larger tetras and the infamous tiger barb will happily shred the guppies fins.

Most small barbs are actually very sociable, and are just given a bad name by the tiger barb and a few others. Smaller tetras, small barbs, other common livebearers, and non-predatory catfish are the best choices for tank mates.

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