By Dr Eugene Larr
The range at which guppies can live covers a range from about 55oF to 100oF. I am sure you realise that there is a much narrower range that guppies like, but it is somewhat amazing that they are such tolerent creatures. While guppies live at 55oF, they do not like it and will do rather poorly. While the higher temperature of 110o F should not be used several reasons, we will discuss one factor of this higher temperature which can be very interesting.
The normally accepted temperature for guppy culture is from about 74 F to 80 F. With this range guppies do there best and will give you the greatest rewards for your efforts.
There is a startling effect on the longevity of a
guppy as the temperature is changed. A guppy raised at 80 F from birth will
probably be dead in 18 to 21 months, while one raised at 74 F will live 30 to 48
months. I have a number of fish which are kept at 69-71°F that are now just
over five years and are still doing fine.
Just as in almost all the other requirements for
guppy culture there are two paths to proceed along when one is considering
temperature. If you want large show guppies you must hold the temperature higher,
somewhere in the 80 to 85oF range. If you want your fish around for a long time
and therefore have enough time to do some genetic experiments, you should drop
the temperature to about 73 to 78oF. There is a happy medium of course, and the
best of both temperature ranges can be had by following this line. When the
young are born place them in a tank at about 82oF. As the young grow into adults,
displaying their full finnage, the breeding fish are selected and put into a
tank which is held at about 74°F, which will prolong their life and keep them
going for many, many months. The fish which are selected for show are held at
the higher temperature (78o F) and are kept on a feeding program such that
maximum size and condition is obtained quickly. This generally causes a show
fish to be past its prime in about 14 to 16 months. This is the price you pay
for large quickly grown fish. It is very important that you keep in mind the
breeders and be careful in your selection of both male and female. Select only
fully matured fish, because it is only in the adults that one can truly see what
their genetics is displaying. How often is the comment "the best looking
fish I have always seem to be found in my tank of culls". This statement
tells us that these people are culling at too early an age, and there fore not
getting the most out of the selection of breeders, as well as show stock in some
I have started to do some work on this problem of temperature and have started a series of tests by asking one question: will a male guppy from a given strain grow to the same size and shape if it is raised at a lower temperature than it's brother at a higher temperature, or is the only way to obtain maximum size and shape closely tied to high temperatures at all times ? So far l have tested only four strains and the results are about the same in each case. The fish raised at the lower temperatures reach about the same size as their brothers who were raised at higher temperatures. I say almost because the fish when compared directly by measuring are slightly different. In the more drastic case, a blue widetail strain, the length of the overall fish was 4.5mm longer in the fish at higher temperature. The average difference in total length was only 2mm. The blue wide tail that was 4.5mm longer than his brothers looked like a giant and it was easy to see a difference of even 1.5mm length. But I will do many more of these tests, before I can arrive at any solid answers to my original question. The fish raised at the higher temperature (85oF) grew the fastest, and were all dead an about 10 months. The fish grown at a lower temperature (74oF) were found be growing slowly but surely all along the way. While they have not totally caught up with their brothers at higher temperatures they are still alive at 36 months and still growing slowly. Who knows, if they live long enough they may catch up. But as I say there are more strains to be tested before we can make any firm statements.
Here is a composite graph of many different strains that will show you the importance of temperature and how all the or factors fall into the temperature complex. Study it awhile and you will see many interesting points that might be of help.
Now for the very high temperature factor I mentioned earlier- When guppies are kept at 110oF they can be maintained with a little care, and when the young are born one will find a higher rates of mutation. The higher the temperature, the higher the mutation rate. If you want to experiment, here is a very easy one to explore. The results are mostly unsatisfactory as is the case with most mutations, but once in a while a good new form may come along, and who knows, you might just obtain a truly spectacular guppy. As the young fish are born at this high temperature, place them in a different tank where the temperature can be lowered a few degrees a day until you get them to 74 F for a growing range. The parents must be kept at the higher temperature all of the time as it is their bodies at the time of cell division that the changes occur.
They will not live long and you must feed with
great care. They will need more food and it is very easy to foul the water at
this high temperature. As you are working in this kind of experiment remember to
make all temperature changes when necessary, very slowly both up and down. If
you have a few extra tanks and would like to do some work along this line, be
sure to keep complete records. Your notes will be of great importance and the
records will be invaluable.
Reproduced from ALA Special Publication Number 4. Guppies date of original publication May 1972. author Dr Eugene Larr.