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Fish breath.

To breathe, most--but not all--fish pump water through their mouth, over their gills and out their gill cover, called the operculum. Their gills transfer oxygen from the water to the fish's blood, hence the bright red color. Like us, fish have hemoglobin to carry oxygen in their blood.

Because fish gills are so exposed to ambient water conditions, they are sensitive to acid in the water and any other contaminants that can damage the gill membranes. This can cause serious problems for marine coastal fish when we flush fresh water too fast downstream, or pollute our waters with heavy metals, pesticides, herbicides, toxic algae or other chemicals.

Not all fish breathe strictly through gills though. In fact, several Florida species can breathe through their skin. The little cryptic mangrove rivulus (killifish) lives in giant land crab burrows. When the dark, sulfurous burrow water has no oxygen, the rivulus can leap up the sides of the burrow and crawl across damp ground, breathing through its skin.

Many tropical fish can breathe air through modified gas bladders, analogous to a lung, with air being taken through an opening in their throat. Ever see tarpon perform their classic surface roll? They are taking air at the surface and have adapted to live in backwaters lacking oxygen. Warm temperate gar and bowfin (mudfish) do the same thing.

Another fish that evolved in nutrient-rich tropical backwaters is the common snook. Young snook less than six inches can sip oxygen from the water's surface film, and thereby survive in mangrove swamps lacking oxygen for extended periods. Once they grow over six inches they can no longer do this and must migrate to oxygen-rich waters.

The most notorious Florida air breather is the exotic walking catfish. During heavy rains they migrate on land carrying water in a pouch to keep their modified gills wet.

Florida natives--American eels and bigmouth sleepers--can migrate on land for short distances breathing through their mouth, skin and gills kept wet with trapped water. Bigmouth sleepers are caught at night (they sleep all day) along creek and river banks where they are foraging on insects, spiders, crabs and shrimp.

By R. Grant Gilmore, Ph.D.
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Title Annotation:The SPORTSMAN'S BIOLOGIST; fish respiration
Author:Gilmore, R. Grant
Publication:Florida Sportsman
Geographic Code:1U5FL
Date:May 1, 2009
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