After the food limit has been determined, this will dictate the population of a tank.  For example a 10 gallon tank of 60 one month old babies is reduced to 20-30 as they grow to adulthood.  The amount of food stays constant and as the population is reduced which increases the amount of food per fish. Reducing the population is necessary to keep optimum water conditions and feeding to promote good growth.  Good guppy breeding practices of sexing the guppies at 6 weeks and culling helps with this reduction. Overpopulated tanks will result in smaller fish since there is not enough available oxygen to grow larger. Overfeeding of what the tank can handle will reduce the oxygen level more effecting growth and weakening the fish.

Catfish and Algae Eaters

Guppy breeders often use scavenger fish such as catfish and Plecostomus to eat uneaten food and algae in the tank. This can actually reduce the amount of food available to the guppies.  Once the food reaches the tank’s floor the food is eaten by the scavenger fish. Since the amount of food is fixed to keep good water quality, the guppies may not get enough food to get optimal growth if eaten by scavenger fish.  I use rams horn snails to control algae and to eat uneaten food.  Snails move slowly so the guppies have a chance to pick food off the bottom. A breeder can use scavenger fish if they reduce the number of guppies to have enough food for the guppies before it reaches the tank’s floor.

Signs of Poor Water Conditions

A guppy breeder can visually tell if a tank’s water conditions are poor.  Even if a tank’s water is clear the ammonia and nitrite level can be at dangerous levels.  Guppies in distress will have fish hovering at the top water surface gasping for oxygen or have loss of appetite.  Hobbyists often view this as a parasite issue and treat the water with medication and exasperate fish’s distress.  The best way to address this issue is to do a 40% water change, filter floss change (sponge rinse in color water to get rid of excess debris) with medication to cover all possibilities. If the issue is water conditions the guppies will improve within a few hours. Often poor water conditions will weaken the fish which opens them up to be affected by bacteria and fungus. I have found that keeping with weekly 30% weekly water changes, cleaning filters/changing floss every 5 weeks (without destroying the biologicals by cold water rinse of ceramic rings), and controlled feeding has dropped my occurrence of sick fish dramatically.

Water changes are necessary to reduce the ammonia, nitrite, and nitrate levels. Nitrates are at the end of the biological aerobic cycle and can be effectively reduced by water changes. Plants help use and reduce nitrates, but not fast enough for the typical guppy population and feeding program. When nitrate levels are too high often sudden death of one or two fish can occur. Dangerous nitrite levels cause nitrite poisoning in the guppy and turn its blood to a red brown color showing a deprivation of oxygen.  When these detrimental compounds are at high levels guppies are weakened and growth is inhibited.

Observing If Guppies Are Fed Enough

Guppies should be able to gain enough weight to show thickness. This means that the guppy is having enough nutrition beyond survival and has extra reserve to build muscle and some fat. Building fat reserves is essential to carry the fish through the next feeding and doesn’t inhibit the process of growing. If a tank’s fish population doesn’t develop a full belly after a feeding period (fix amount of food) there are too many fish in that tank.  That is a signal to cull the tank, divide the fish to another tank, or split the fish to another tank by separating the sexes.

Overfeeding is indicated if after 5 minutes there is remaining food after feeding.  Excess food will break down and increase the ammonia concentration. Don’t be fooled by fish madly swimming at front of the tank wanting more food as you go by after feeding. Look at the surface of the tank to make sure all the food is gone. Guppies can get lazy and rather have more food put in front of them instead of searching for the remaining food.

I have overfed tanks by doubling the amount of food by feeding 6 times a day instead of 3 times. At the time I thought this would improve the size of the guppies with poor results. The increased amount of food increased the fish waste causing dangerous levels of ammonia, nitrites, and nitrates.  Tanks crashed and fish became ill. I lost many fish and it delayed the progress of my breeding program. Unfortunately I attempted this several times, until I looked deeper to understand the causes.

Conclusion

Optimizing the water and feeding is a good way to evaluate the genetic growth potential of a line of guppies.  A line of guppies from a winning line should be able to produce competitive guppies at the show bench if good raising and breeding practices are done.  If water conditions and feeding practices are at a constant then the breeder can focus on steps to improve a strain of guppies.

I will plan to write future articles on breeding practices to improve a strain, but here are a few suggestions to maintain or improve size in guppies. Maintain 2 or more lines of a color type of guppy and cross after the 3rd generation. I have found that a line of guppies can have a reduction in size due to brother/sister inbreeding after 3 generations. Crossing to a related line invigorates the health and growth of the fish due to having more genetic diversity from the line cross. If the line(s) are always small then an outcross to a larger line with the same color type can be done and then inbred to fix desired traits.