The Importance of “Light” to Koi, Goldfish and Aquarium Fish in General

Why Can’t Koi and Goldfish Live in the Dark? Is “Sunlight” Absolutely Necessary?

It bears mentioning that light has several effects on fish which can ensure your success or failure. Full spectrum lighting with sufficient intensity and spectrum will stimulate the growth of healthy, green sessile algae. Algae benefit the fish in numerous ways including:

  • Providing edible phytoplankton for the fish to consume
  • Providing for the reduction of Nitrate in the environment
  • Raising dissolved oxygen during its photosynthesis during the photo-period.
  • The algae layer is slick, and preferable to any other surface for fish contact
  • I strenuously encourage the hobbyist to allow as much sessile green algae to remain on the ornamentation and sides of an aquarium as is aesthetically tolerable.
The Importance of "Light" to Koi, Goldfish and Aquarium Fish in General
These koi are eating in shallow water but they may also “bask” in shallow water, as well. Ask any experienced hobbyist.

Lighting also provides the fish with certain metabolic capabilities. It is true that without a full spectrum light source such as natural sunlight or biologically accurate full spectrum fluorescent bulbs, the fish will not be able to activate Vitamin D in their dermis and will eventually suffer calcium abnormalities, which may stunt growth or depress the immune response.

Sunlight Improves Koi, and Fish Color

No one who is experienced in this hobby will argue that full spectrum illumination or sunlight will enhance and improve skin condition and color in Koi, goldfish and pond fish.

Dr Erik Johnson is a Marietta, Georgia Veterinarian with a practice in small animal medicine. He graduated from University of Georgia with his Doctorate in 1991. Dr Johnson is the author of several texts on Koi and Pond Fish Health and Disease as well as numerous articles on dog and cat health topics.