Nature Bulletin No. 264-A   April 8, 1967
Forest Preserve District of Cook County
Richard B. Ogilvie, President
Roland F, Eisenbeis, Supt. of Conservation

****:FISH AT NIGHT

Most people take it for granted that fish are creatures of perpetual 
motion and go swimming day and night. On the contrary, it appears that 
each kind has a rather definite daily routine with certain hours for quiet 
rest or sleep, and other hours for moving about in search of food. As a 
rule, fish active in daylight rest at night as if they were asleep. 
Sometimes they lean against rocks, with their fins folded, or creep into 
holes and among vegetation. Fish scientists have learned that almost 
every kind of fish makes regular daily trips between shallow and deep 
water. Lampreys, suckers, smelt, redhorses, wall-eyed pike and a few 
other kinds are known to make their spawning migrations and lay their 
eggs at night.

The different kinds in any body of water are divided rather clearly into 
a day shift and a night shift, with still others which are most active at 
dawn and dusk. Fish active in clear well-lighted water are sight-feeders 
and have large well-developed eyes; while those active at night, or in 
deep or muddy water where the light is dim, depend mostly on their 
keen senses of touch and taste.

The best time to fish for channel catfish, bullheads, or eels is at night. 
At dusk these fish come out of their hiding places in the muddy bottoms 
of lakes and streams, to scour the shallows and other rich feeding 
grounds until sunrise. At night, the eel is known to crawl out on land in 
swamps and dewy meadows to search for frogs and crayfish. A11 such 
fish have extremely delicate senses of touch and taste in cells scattered 
all over the body. In addition, the catfish, including the bullheads, have 
a pair of "whiskers" or barbels, often several inches long, extending 
outward from the corners of the mouth; two smaller pairs under the chin 
that point downward; and another smaller pair on the nose that point 
upward. If one of these barbels touches anything edible, as they skim 
over the bottom, the fish whirls like a flash and grabs the morsel as 
easily as if it were in plain sight.

Many anglers prefer to fish at night with artificial baits. This is possible 
because most fish are equipped with a special sense that can detect very 
slight movements in water. It is supposed that this sense is centered 
mostly in the "lateral line" -- a row of pores running from head to tail 
along each side of the body. It is so sensitive that a black bass can catch 
a small minnow in a large tank in total darkness, and a blinded pike can 
grab the tip of a pencil moved slowly through the water.

The habit some fishes have, of congregating in schools, depends 
primarily on eyesight. When evening comes, schools of young 
bullheads and herrings break up and settle to the bottom where they rest 
until morning. During the day, in clear water, almost all fish are able to 
change their color to correspond with the background, However, at 
night, they all become pale -- very much as do fish that live-in caves or 
muddy water. In muddy streams and lakes, fish are forced to live in 
almost continual night because the suspended silt cuts off the sunlight. 
In the Mississippi, for instance, practically every kind of fish is 
specially adapted for living in darkness. For example, the catfishes, 
sturgeons, paddle fish, dogfish, carp and many of the minnows have 
barbels. Sight-feeding fish in streams and lakes suddenly muddied by 
rains, frequently go hungry and lose weight until the water again 
becomes clear.

How can you tell if a fish is sleeping, when he never shuts an eye?