Do Fish in an Aquarium Require Darkness?

Virtually all aquatic species need periods of light and darkness. The only exception are the freshwater blind cavefish and the marine creatures that live in the deepest sections of the ocean where sunlight will never reach. Aquarium fish are tropical species that normally live in habitats where they get periods of sunlight followed by several hours of darkness. Some species have biological cycles triggered by light or the absence thereof. As keepers of aquatic ecosystems, aquarists should understand the relationship between light and dark cycles as they apply to their tanks. The trusted staff at Aquatic Warehouse, a leading provider of fish tank supplies, would like to share some details on whether fish in an aquarium require darkness.

Why Fish Need Darkness

Years of research by marine biologists have determined that fish don’t sleep in the same way mammals do. In fact, some marine mammals such as dolphins don’t sleep in the same way humans do even though we share many characteristics. All aquarium species need rest, and many of them choose to rest when the lights are off. When fish rest, they shut off certain biological processes while activating others, which has a restorative and sometimes healing effect.

Resting Behaviors

Some species simply float in place, although some may prefer to rest part of their bodies on the substrate, plants, or decorations, while others will even spin a “nighttime” cocoon to hide from predators. In saltwater reef tanks, some species will partially burrow in the sand. Schooling fish may choose to hide, which is why it’s important to provide them with plants and decorations such as rocks and driftwood.

Nocturnal Fish

Plecostomus are the most common nocturnal species found in freshwater aquariums. You may see plecos seemingly enjoying periods of activity in the daytime, but they really come alive at night, which is why they need darkness. Most invertebrates such as ghost shrimp are also nocturnal, but this doesn’t mean they’ll bother aquarium mates at night.

Setting Up Day and Night Cycles

A few aquarists set up their freshwater or reef tanks in spots where they’ll get partial sunlight. This is a great idea for plants, fish, and invertebrates, but it may also require some adjustments in terms of temperature control and keeping algae in check. Most fish keepers opt for aquarium lights because they aren’t conducive to extreme algae bloom. With this in mind, it’s never a good idea to keep the lights on at all times. At the same time, you should also try to keep the lights in periods that match sunrise and sunset. If your aquarium lamps have programmable timers and you’re an advanced aquarist, consult the Farmers’ Almanac to set them up through the seasons.

What Happens When Fish Don’t Get Adequate Darkness?

You may have seen lavish aquariums set up in restaurants and nightclubs. These tanks are illuminated for the benefit of diners and revelers who want to appreciate aquatic species, but the lights are turned off after a few hours. You generally should give fish a dark period of about 12 hours. Failure to do so could result in stressed species that are more likely to get sick.

Though aquarium fish need some darkness, they also need high-quality lighting. At Aquatic Warehouse, we carry only the best in LED, T-5, and other types of lighting, and we also carry everything else you need to properly care for your tank, from aquarium monitors and controllers to beneficial bacteria and filtration. Stop by our store in Kearny Mesa, take a look at our website, and give us a call at 858-467-9297 if you have any questions.