Guppies FAQs

All new guppy-keepers have similar, exciting questions. Read below for the answers.

Question 1: How soon can guppies multiply?

Females mature at about 3 months of age, perhaps sooner in a warmer tank. Males sexually mature somewhat sooner. The males will develop a modified, pointed anal fin called gonopodium, after several weeks. The male with the least desirable traits often impregnates the females, and all chances of controlled breeding is lost. This is a good reason to separate them before the male can develop his gonopodium.

Question 2: Is my guppy pregnant? Where is the gravid spot?

If your female has been around other males, then chances are she is pregnant. Females from pet store tanks are usually pregnant. Signs of pregnancy are a large belly, a boxy-look from the front view, and a darker gravid spot. The spot, under the fish's tail, is like a stained-glass window where the fry come out. Near the day of delivery you can sometimes see eyes of the unborn fry as tiny black dots.

Question 3: When will my guppy have her babies?

There really is no telling. You will just have to keep a close eye on her as she gets larger and her gravid spot gets darker, because there are no definite signs. Sometimes a female will become rather still and solitary near birthing. If you know when she had her last drop, you can expect another drop in about 4 weeks or so.

Question 4: How do I save the fry?

The best way is to have a separate tank loaded with fake or live plants and a small box filter. Before the female is to deliver, put her in this tank, and when she drops the fry will have lots of cover in which to hide. The mother will sometimes make a meal of them if she sees them, since she is very hungry.

Question 5: How and when can I tell the sexes apart?

The answer is, believe it or not, at one week of age! Just look for the gravid spot which every female has. Use a small magnifying glass and a flashlight. When separating them, if there is a question as to whether a guppy is male or female, put it with males. Keep in mind that there is no urgency to separate them until the male's anal fin begins to look pointed. He cannot inseminate females until his gonopodium is developed.

Question 6: How can I make sure who the father is?

Since a female stores sperm and has often 4, sometimes 8, drops from just one fertilization (this is called "superfetation"), it is impossible to know (unless you buy a virgin female and mate her). If the female is fertilized again at the time she drops her young, that male's sperm should take over and the next drop should be his fry.

Question 7: When do guppies start to get their colour?

This depends mostly on genetics. Some strains get colour sooner than others. For instance, the reds that you see in this website did not show any red until 6 weeks of age. The Moscows display most of their colour by the time they are 6 weeks old. Half-black males typically show dark caudal peduncles from about one week of age. Rate of development makes a difference as well. If fry are kept in cool water with infrequent water changes and dry food only, they will mature at a much slower rate.

Question 8: When is it safe to put my fry in the tank with adults?

Those hobbyists that are serious about seeing their fry develop to their full potential will not mix fry with adults. Though unproven, it has long been held that older fish release a pheromone which inhibits growth in fry. Also, adult fish produce much more waste than smaller fish, thus causing lesser water conditions than is needed for the healthy development of fancy guppies. Also, growing fish need more food than older fish, and usually find it difficult when forced to compete with adults; feeding more food simply contributes to the problem of poor water quality.

Specifically, however, the question deals with "safety", which implies that one wants to know when the fry will be able to survive the adult tank. This is the question many people have when they do not keep separate tanks for the fry to mature in. Assuming there are no other species of cannibalistic/aggressive fish in the tank, fry should be able to live with adult guppies when they are large enough so as not to be considered food, compared with the size of the adult guppies. No age can be specified since development in size varies.

Question 9: What kind of home does my new guppy need?

Many people new to guppies think a fish bowl of 1 or 3 gallons is sufficient. However, this is incorrect. A guppy is very active and needs space, and space also gives you the benefit of seeing the amazing colours of the fish in all their glory. Also, they are social fish and it is a sad injustice to submit one to solitary confinement. A group of three, a male and two females, is the minimum, and for this you need at least a 4 to 5 gallon tank.

Question 10: Does that mean a large investment then?

It is not necessary to spend a lot of money on a guppy set-up. All that is needed is a tank (I suggest a 10 or 20 gallon tank in the beginning as there is more room for errors than in a smaller one!), a filter, and possibly a heater. Some people find great bargains on secondhand fish tanks and accessories. Remember that the larger the tank your fish have, the better, so get the largest you can afford.

Question 11: What plants or decorations do guppies need?

Guppies do not need plants or gravel; they do not even need a heavy-duty power filter. An inside box filter powered by an air pump is all that is necessary for biological and mechanical filtration and aeration (for a 5 to 10 gallon tank). You can leave out the charcoal and weigh the box down with marbles. Paint the outside bottom of the tank with a dark paint (black is a good choice). This gives a smooth bottom for the guppy arena and no small stones will gather debris or leftover food where the guppy cannot retrieve it. Also, it is more comfortable for the guppy to rest at night on a bottom of smooth glass than a bed of gravel! This is the cleanest possible way to keep guppies.

Question 12: How soon after setting up a new tank can I add fish?

An aquarium takes 6 weeks to cycle in order to be safe for a full stock of fish.  If you have chosen fish to cycle your new tank, here are some tips to help them survive: add a bacterial supplement such as Cycle, provide extra aeration (water surface agitation), and remove 10 - 20% of the water daily with vacuuming.  Add only a few inexpensive fish at first, and then slowly add more.  You can also choose fishless cycling, which will spare the lives of your first fish. 

Question 13: What kind of filter should I use?

Power Filter

A 10 gallon tank can have a large-size box filter or an outside power filter, and anything larger than a 10 gallon tank should definitely have a power filter. The filter I recommend is the Aqua Clear. A mini AquaClear is sufficient for a 10 gallon, and the "150" is excellent for a 15 or 20-gallon tank. There is no need to constantly replace filter media, the foam should last years (rinse only in tank water), and once again, carbon is unnecessary as a medium. You may want to add an air stone when using a power filter. They do create some aeration, but more is usually better. I do not recommend under gravel filters for guppy tanks. They cause problems when you clean them, they are really not enough to keep a tank clean, and when used in addition to an above gravel filter, they are in an over-kill situation anyway.

Question 14: How often do I clean the filter, and what is the best way?

Inside box filters should be cleaned when they start getting brown throughout the floss. It depends on your number of fish per gallon and tank maintenance how often this is, but it should not need to be cleaned any more than once a week. This is the way I clean filters: Remove the filter and change MOST of the floss. Carefully keep a small portion of the used floss and insert this between the new floss to retain some of the good bacteria and to help "seed" new media. This is the best way to keep the essential nitrifying bacteria that breaks down the ammonia which is produced by fish waste. If you keep carbon/charcoal in your filter, it should be rinsed with tank water (the chlorine in tap water destroys the bacteria) and replaced monthly.

Power filters should have their media rinsed weekly, and they should be removed from the tank and cleaned thoroughly, once a month, avoiding contact with chlorinated water.

Question 15: Do I need a heater?

Aqua Heater

Heaters can be rather expensive, so this is a common question. Usually, the answer is "yes". A guppy should have a temperature in the mid 70's F. If the temperature drops at night any more than 4 degrees, I recommend you use a heater. Drastic drops in temperature are stressful and eventually can cause problems like ich. If your normal day time temp is, for instance, 82°F (too warm) and the temp drops to 76°F at night, you may want to make sure the temp drops only 3 degrees or so at night with the use of your heater.

Question 16: How often should I feed my fish?

Fry should be fed several times daily. For the best growth, try to feed live food often. Adults should be fed less, with a diet lower in fat. Two or three times a day is the maximum for mature fish, and the feedings should be rather small.

Question 18: Can I sell my extra guppies?

There are some smaller pet stores that will take in guppies, however, many do not. It is not a good idea to raise guppies with this intention, because you only get about 1/3 of the selling cost of the fish. They must be close to maturity as well, and it is usually not worth the expense and effort to raise guppies for this purpose. However, if you do have lots of space to raise guppies, selling your extras, or trading for supplies can offset the cost of raising the guppies in the first place. Check with local fish stores in advance.

Question 19:  What other species can I mix with guppies?

Other peaceful fish which tolerate the environment that exists in their tank.  For instance, if your water is rather hard as guppies prefer, do not mix tetras or other soft water species with them.  If you keep salt in your guppy tank, choose other fish which tolerate/enjoy this as well.  Corydoras catfish are found to be excellent with guppies since they simply mingle amongst themselves on the aquarium floor and clean up unwanted food.  I find salt does not affect them.  Also, the similar livebearers, platies and mollies, mix fine with guppies.  Never mix aggressive fish with guppies such as bettas which may attack the fancy guppy.  Guppies do not actually breed with other species, but fancy guppies and non-fancies will.

Show quality guppies generally do best in a species tank (on their own) because comparatively the males swim slower than other fish with their body size due to their elongated fins.  They may not be able to compete for food and aggression is often directed at them.  Whenever adding a new fish (guppies or otherwise after a suitable quarantine period), watch to see if any fighting is taking place.