Five Precautions when Releasing Fish

1. Land the fish as quickly as possible minimize exhaustion
2. Handle the fish as little as possible, using wet hands.  Do not squeeze the fish, and minimize it time out of the water.
3. Keep any fish which is bleeding from the gills or throat or which shows air bladder damage.
4. Release fish gently, do not throw them into the water.
5. Do not release fish which have been held in a cooler or in the bottom of the boat.

It is important to land a fish as quickly as possible.  Warm water increases the oxygen demand while decreasing the availability of oxygen in the water.  Exhaustion can occur rapidly, reducing the fish ability to breathe. Acidity build up in the muscles and blood can occur as the fish becomes fatigued, and can be diminished by the loss of carbon dioxide through the gills as the fish breathes. So a fish too exhausted for proper breathing will have great difficulty in regaining oxygen in the bloodstream and in reducing acidity.  Gently pulling the fish through the water will sometimes help stimulate breathing but pulling the fish forward through the water also reduces oxygen uptake and can damage gill filaments.  If a fish does not regain its equilibrium after a couple of minutes, it probably will not survive.

Handling of the fish to be released should be done with wet hands and should be held to a minimum.  The mucous, or slime layer covering a fish is a protective coating which keeps disease organisms out of the body, retains the salt balance within the body, and actually helps the fish slide through the water easier.  Handling methods and abrasion which removes parts of the mucous layer can therefore make the fish more susceptible to funguses and bacterial infections.

Since infections often take several weeks to incubate, a released fish can appear quite vigorous as it swims away but may still be doomed.  The loss of body salts through skin areas not protected by mucous can also severely upset the metabolism and body functions.  Many fish can be unhooked at the side of the boat without handling, which is one of the best methods.  Landing nets with new softer materials are also very safe.  Fish with sharp teeth can be gently held by the jaw.  When holding a fish by the body, wet hands will help protect the mucous layer, but try not to squeeze the fish.  Vital internal organs can be damaged very easily.

Fish which are bleeding when landed or unhooked have usually suffered severe tissue damage.  A small amount of blood seeping from the hooking site in the jaw or tongue will probably not harm the fish.  But if the bleeding is from the gill filaments because of hooking or handling damage, the fish should be kept.  It is unlikely that a severely bleeding fish will survive, especially in warm water.  Fish hooked deep in the throat or stomach may survive if organs have not been critically damaged and if the line is cut and hook left in the stomach.  In some cases hooks have been seen to dissolve in stomach acids, although gold or nickel-plated hooks generally prevent this possibility.

Fish brought up from the deep water experience reductions in external pressure which can cause gas bubbles to form in the blood (i.e. the "bends").  In more serious cases, the swim bladder can expand and actually extend out of the fish's throat.  Most fish taken in the Western Basin of  Lake Erie are caught in shallow enough waters that pressures changes are not dangerous.  Fish taken in deeper waters like the Central or Eastern Basin are more susceptible to damage from pressure changes.  Yellow Perch taken from the bottom waters are frequently seen with their air bladders protruding from their throats.  It is highly unlikely that these fish will survive if released.

Exchanging of smaller fish in a cooler for bigger fish is illegal if you have a limit of fish in your possession, and in nearly all cases is simply wasting the smaller fish.  A fish in a cooler or in the bottom of a boat is not only exhausted perhaps beyond recovery, but has suffered severe abrasion, resulting in the loss of scales and the mucous layer.  Since fish can only breathe in water, blood oxygen will be critically low, and the gill filaments may have dried out, rendering them useless when the fish is released.  Recent studies on Lake Erie fishes have shown most game fish species to be sensitive to both the abrupt increases and decreases in temperature.  So a fish removed from the warm water, dropped into an ice chest and later thrown back into warm water suffers two separate thermal shocks in addition to it other injuries. 

Source: Ohio Sea Grant College Program Ohio State University Extension, Lorain County, 42110 Russia Road, Elyria, Oh 44035-6813.