While platy fish cannot see as clearly in the dark compared to daylight, they have some ability to navigate, find food, and detect predators in dim lighting because of light-sensitive rod cells in their retinas. However, complete darkness impairs their vision, and proper lighting is needed for their health.
Platies, like many fish, have eyes adapted for underwater vision.
Their eyes are laterally positioned on each side of their head and are specially adapted to allow light to pass through the cornea and lens to the retina.
The platy retina contains rod photoreceptor cells that are sensitive to low light intensities.
This gives them better vision in dim lighting compared to us humans.
Platies rely heavily on their vision at night, so proper low-level lighting in tanks is crucial for their ability to navigate and find food after dark.
Our observation suggests platies can see fairly well in low-light conditions compared to other freshwater species.
We tested the visual acuity of some freshwater fish species, including platies.
Platies were found to have higher visual acuity in low light compared to goldfish and guppies, though not as high acuity as zebrafish.
This indicates platies are adapted to function visually under low light intensities.
Their retinas contain rods and cones to detect light/dark changes since their eyes are adapted to be open constantly.
In the wild, platies are most active during daylight hours. Their eyes accommodate daytime vision.
However, their retinas have enough rod cells to allow vision at night and in murky waters.
Their visual acuity and color discrimination diminish in low light, but their vision likely remains functional.
Lateral lines running along their bodies allow them to detect vibrations, movement, and location even in complete darkness.
This is a key non-visual sense platies use to navigate in the dark.
Platies require some darkness to maintain proper circadian rhythms. In the wild, they experience a natural day-night cycle.
Total darkness cues their bodies to produce melatonin and sleep.
In captivity, turning tank lights off for 10 – 12 hours daily provides necessary rest periods.
However, platies do not require complete darkness to sleep. Their vision remains partially active even in low light for nighttime vigilance.
Mimicking natural daylight/nighttime cycles with tank lighting benefits platy health and circadian rhythms.
The transition from light to dark and vice versa can be stressful for platies if not appropriately handled. Gradually adjusting lighting is recommended.
While platies can adapt to low light, keeping them in complete darkness for extended periods can lead to lethargy, inflammation of the eyes, and eventual death without proper light exposure.
There are still some unknowns around how well platies can adapt long-term to living in complete darkness.
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