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Nighttime on the Reef: Characteristics of Nocturnal Fish and Nocturnal Aquarium Setup

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Nighttime on the Reef: Characteristics of Nocturnal Fish and Nocturnal Aquarium Setup

Marine fish can be classified into groups, depending upon when they are most active. "Diurnal" fish
are those that are primarily active during the day; those that are most active during the night are
called "nocturnal." Some fish are especially active at dusk and dawn, and are referred to as
"crepuscular." Various marine invertebrate species can also be classified into one of these three

In aquarium settings, some nocturnal species, such as the cardinalfish, can adapt to becoming more
active during the day. Others, such as the Longspine Urchin remain primarily nocturnal.

Nocturnal Crepuscular Diurnal
Cardinalfish Barracuda Angelfish
Big Eyes Jacks Anthias
Soldierfish Lizardfish Butterflyfish
Squirrelfish Goatfish Wrasse
Pinecone fish   Damselfish
Scorpionfish   Gobies
Snappers   Hawkfish
Eels   Puffers
Sea bass and groupers   Triggerfish
Flashlight fish   Parrotfish
Many invertebrates including lobsters, shrimp, crabs, and other crustaceans, mollusks, polychaete worms, and starfish
 Polyps of many corals, such as Gorgonian, Torch coral, and Tubastrea

Characteristics of nocturnal fish

Depending on when they are most active, fish may have developed certain physical and behavioral
characteristics. For instance, nocturnal fish:

In general, are not designed to swim as fast as diurnal fish.

Tend to have larger eyes.

Tend to be more solitary, rather than living in large schools.

Are often more shy, and during the day are found hiding in caves or under overhangs.

Are often red or yellowish brown in coloration since these colors are absorbed by the water and are
the first colors of the spectrum to become indistinguishable as light levels drop.

Tend to be carnivores versus diurnal fish who are often herbivores or omnivores.

May have a well-developed lateral line, like the Dwarf Scorpionfish, which allows them to sense water
movement as an aid in finding prey in the dark or low light.

Setting up nocturnal aquariums

To establish a nocturnal aquarium you will need to create an environment with many caves and
hiding places. Try to arrange the live rock and low-light corals to make hiding places that will still
allow you to observe the nocturnal life under low light.

Even though it is a nocturnal aquarium, you will still need to provide light, especially if you will be
including corals. In most cases, a reef aquarium with the intensity of lighting needed to maintain both
live corals, and nocturnal fish will need to be very tall and wide. This will allow it to be aquascaped in
a manner to make large enough caves and hiding places for the fish to get away from the light and
feel at ease.

For nighttime viewing, a variety of lighting systems are available to allow you to see the inhabitants,
yet provide the type of light that will bring out the nocturnal life. These include special lights often
termed "lunar lights" or "moonlight lights." These lights produce light that is bluish in color and/or
simulates moonlight. They are long lasting, draw little energy, and generate virtually no heat. Various
styles can be mounted on the glass or in the canopy. Understanding the response of various
organisms to changing light conditions is the subject of ongoing study. Many aquarium experts claim
success simply with twelve hours of daylight and twelve hours of simulated moon light. You can easily
automate this cycle using a timer. Because some corals and organisms appear to need a period of
total darkness before moonlight appears, you might delay turning on the moonlighting for an hour
or more after turning off daytime lighting.

When choosing the inhabitants, consider their ease of care and temperament, since many may
require extensive experience or be quite aggressive.

(article by Veterinary & Aquatic Services Department, Drs. Foster & Smith)

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