Daytime Fish Behavior

Most tropical fish species are diurnal, meaning they are active during the day, when the light allows them to use their eyesight to hunt and avoid predators. In the tropics, day and night are of similar length, so the fish have a great deal of activity to pack into 12 hours. As a result, the aquatic environment in the rivers and lakes there are a whirl of color and activity. Large schools of fish gather on the edges of weed beds and, at the surface, larger fish prowl the deeper open water areas.

Do fish have a daily schedule?

For fish in the wild, the first few hours of the day are taken up by voracious foraging in order to top up their energy levels after a night with little feeding. Just after dawn, lake fish move into the shallow-water littoral zones, which are rich in invertebrate prey. Having satiated themselves, they may move back to the relative safety of deeper, open water during the afternoon.

Alternatively, younger fish, especially, may seek out hot spots at the water surface or in very shallow water, where they can bask in the sunshine. Spending time in warmer water accelerates their metabolism and speeds up the process of converting food into growth. Larger fish have fewer natural enemies. Nonetheless, fish are at great risk from predators such as birds while basking. As birds are primarily visual hunters, they pose the greatest risk during daylight hours. The first realization that a fish-eating bird is at large may be a shadow passing overhead. As a result fish tend to be extremely sensitive to movement above the
water surface, even those species that have been kept in captivity for years — old habits die hard. Basking fish are even more acutely aware of the danger and dart into deeper water at the first sign of movement nearby.

Do fish use the sun to navigate?

Fish often have stereotypical patterns of movement each day, which they follow throughout their lives. This might involve moving between their overnight refuge to one or more foraging grounds and back again during the course of the day. To do this they can navigate by the sun, using its position in the sky to assist them in deciding their traveling direction.

What do nocturnal fishes do during the day?

While the diurnal fishes bustle around the habitat in perpetual motion, their nocturnal counterparts spend the day in concealment, waiting for dusk. Fish such as the upside-down catfish (Synodontis nigriventris) hold station underneath sunken wood or rock in their familiar inverted position throughout the day, occasionally darting out for food but concentrating most of their feeding effort in the hours of darkness. In the deeper waters of the African Rift Valley, where very little light penetrates, Synodontis and other adult catfish are active throughout the full 24 hours. However, the juveniles, which live in shallower water, show the typical nocturnal pattern and hide during daylight.