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King Of The Aquarium - The Guppy

If a ‘king of the aquarium’ is mentioned these days, it’s usually in a discussion about discus. However, the regal post was held not so long ago by another fish, also very beautiful, and easily accessible to just about every aquarist – a fish that nowadays we see so often that their beauty has become commonplace. This fish is, of course, the guppy, Poecilia reticulata.

By 1960 the many forms of the guppy we know now were well-established – veiltails, cofertails, flagtails, swordtails, lyretails, pintails, speartails – and in Aquarist and Pondkeeper editions (now Today’s Fishkeeper) from the 1960’s nearly every issue included something about the guppy. In an open show one (non-guppy fan) person was upset that there were as many classes for guppies as for the rest of the species combined – a view not held by others on the letters page who couldn’t get enough guppy stories and activities.

These little fish rightly deserved their popularity, and continue to warrant more than the passing glance for the familiar and boring that they now get in the aquarium shop. Next time you are browsing the ranks of fish, take another look at the guppies and try to see them as though you haven’t seen them before. The range of colours and patterns, the variety of fins – all this in an active, busy little fish that is happy to be seen at the front of the tank. What other fishes in the shop can truly compete with this?

Fortunately the guppies still have their adherents, and if you think the shop ones are attractive, then try visiting a fish show to see the pure-bred strains in all their glory. Although guppies are easy to breed, and new mutations arise easily, that can be nurtured into new strains, this is also their downfall. A male guppy will mate with a female guppy at every opportunity, and once mated the female retains the sperm – one mating can fertilise many broods. The guppies don’t care if they mate with another guppy of the same appearance, and a bunch of mixed guppies in a tank will, within a few generations, reduce to the lowest common denominator in terms of appearance – a rather brownish fish, with some colour in the tail. To keep a strain of guppies pure and producing offspring as beautiful as their parents takes work, rigorous culling of the offspring, and enough tanks to keep the sexes separate from an early age. Just as multihued plasticine, if mixed, rapidly reduces to brown, so a collection of beautiful guppies of mixed strains will produce inferior offspring.

Although breeding guppies is fun for beginning aquarists, and easy to do, each generation will probably lose a little colour. This can be minimised by buying your original stock all from the same strain from a breeder. Be aware that the fish sold in the fish shop under a particular name are unlikely to be of pure stock, and the offspring are unlikely to be the same as their parents.

All this gives the serious fishkeeper ample material to work with, as well as the beginner who just wants a pretty fish that is likely to stay alive. Some fishkeepers start with a guppies and move on to other types of fish – others find that their guppy interest can grow in complexity and fascination as their experience increases.
If you are just starting out, the guppy is an amenable and peaceful little fish. It prefers harder water, but will adapt to a pH either side of neutral (6 – 8). It will share a tank with any peaceful fish, and although not advisable will cope with remarkable fluctuations in temperature. I once had a tank of baby guppies growing (or supposedly growing) in a rearing tank. All seemed healthy, but didn’t seem to be doing much of a job of growing. It was some while before I realised that they had actually been living in an unheated tank for their whole lives, during a particularly cold winter. Similarly, when a heater malfunctioned and I came home to find the water temperature near the top of the scale, the guppies continued about their business while less hardy tank mates had succumbed. This adaptability and hardiness has led to them forming populations in many parts of the world. Some of these are down to deliberate introductions (the guppy is also known as the mosquito fish, along with several other live bearers, and is used to keep down mosquito larvae) and others to accidental releases/escapes, but the guppies settle in regardless. There is even a population in England living in the warm outflow from a power station.

Although hardy, guppies are short-lived fish. Their motto is ‘live fast, die young’. As soon as the young can be sexed they will have started mating, and will continue doing so at every opportunity throughout their lives. As a results the males are permanently stressed from constant performance and chasing the females, while the females have to cope with producing up to forty live young every month. Although they give birth to live young, this is not a true pregnancy in the way mammals become pregnant. A mammal baby is plugged into its mothers blood and air supply through the placenta, and grows on foods supplied through the mother’s bloodstream. A guppy egg is simply retained inside the female, where it hatches like any other egg. The little fry feeds on the yolk sac that was contained within the egg until it is all gone, when it must start to feed for itself. Even though the female is not providing the food for this mass of offspring, their physical size alone is stressful enough. A gravid (pregnant) female guppy often looks as though she is about to explode, with the skin stretched taut over the mass of her offspring. The so-called gravid spot, the black area at the back of the abdomen which is supposed to show up when the fish is gravid is, in my experience, misleading. Some guppies have them all the time, some never do. A square shaped guppy with the skin straining at the seams is unmistakeable enough. If left in a community tank she will try to find a quiet corner near the surface to give birth. Unfortunately her tank mates will generally follow her about to snap up the tasty bites as they emerge, so if you hope to rear any she is best moved. The birthing/rearing tank should have some plant cover and a sponge filter (an internal one will devour the new babies). It does not have to be elaborate – a bucket with a heater, sponge-on-a-stick type filter and a bunch of elodea will do perfectly well. The ‘breeding traps’ sold for this purpose are not to be recommended. In my experience they result in extremely stressed fish, who may abort or die. A bucket is cheaper and well within the means of most people.

Once the birth is over the female should be removed, and the little guppies will get down to the serious business of eating and growing. As soon as they are born they shoot towards the surface, and will remain there for a few days before starting to venture down through the depths. They consume prodigious quantities of food, and will be big enough to go into the main tank or be sold after a couple of months. At first all the little fish look like females, but as they get bigger the pelvic fins of the males elongate into the long thin spike that is the gonopodium, with which they insert the sperm into the females.

Regardless of your level of expertise or your tastes in fish colour, somewhere in the guppy world there is a project that will capture your attention, be it a new colour variation for your community tank or the longterm breeding of a whole new strain. Next time you are in the fish shop give the guppies another look – familiarity does not have to breed contempt.

This article has been kindly provided by Kathy Jinkings and cannot be reproduced without her permission.


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