Do Your Guppies Have Poor Eyesight?

My original "colorless" guppy strain, dubbed "See-Thru"

Managing to keep guppies alive and deliberating altering their color patterns is difficult. Thank goodness that we have scientists working in labs to help us understand the factors affecting guppy health and color genetics. A case of point is a study I recently came across with the forbidding title: Experience-Dependent Color Constancy in Guppies (Poecilia reticulata) by I.E. Intskirveli, M.O. Roinishvili and A.R. Kezeli (NEURAL PLASTICITY VOLUME 9, NO. 3, 2002).

Find the paper here: http://www.hindawi.com/journals/np/2002/487292/abs/

The authors discovered that keeping guppies under constant light level illumination degrades their ability to distinguish colors. In the wild light levels are constantly changing, so a bright red under bright sunlight will become a much darker color under shaded areas or in the failing light of the evening. The guppy has to make a "mental" adjustment, allowing it to see a red spot as being the same color under the different lighting conditions. Humans have this same ability to see colors like red as a constant color under different lighting conditions, a fact revealed in a photograph shot in dim light where colors no longer look natural, unless your camera automatically compensates for the change in the color temperature and intensity of the light. Constant light illumination reduces the ability of wild female guppies to distinguish colors on the wild male that advertise fitness with a very specific orange color. My colorless guppies would have a selective disadvantage in the wild because female guppies would probably ignore them.

Given that most aquariums and fish rooms are under constant illumination, it is probably a good idea to keep the fish room dimly lit at night so that the guppy's vision system is at least exposed to two different lighting levels. The guppy's ability to forage for food or make the right mating choice would otherwise be degraded. Since I keep my brine shrimp hatchery lit at night, and I have windows to the outside of the fish room, I do not think this is an issue with my particular context. But you might want to check yours. Consider leaving a low wattage lamp on during the night. The other advantage of a night light is that the fish won't be startled to the point where they jump out of the tank or injure themselves when the light suddenly comes on in the morning.