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Page 194

Why Saltwater Fish Are Different

Although freshwater species and saltwater species appear identical in form, freshwater fish would die if placed in salt water, and vice versa. The reason: Although both types need salt to survive, they get it in different ways.

Salt has a tendency to diffuse from areas of high concentrations to those of low concentrations. Therefore, freshwater fish lose the salts in their body via osmosis. To counteract this loss, the kidneys of freshwater fish rid the fish of water while retaining salts. Freshwater fish have glands that retain salts as the fish moves through the water.

Saltwater fish don't need these glands. However, because saltwater fish have less salt in their bodies than is in the water around them, they tend to gain saltand lose water. To compensate for this loss, saltwater fish actually swallow water, and eliminate excess salts via their respiratory and digestive systems. (That's why a mouthful of ocean water tastes terribly salty, but you still shake some salt onto your codfish fillet.)

Otherwise, saltwater fish are biologically and physiologically much the same as freshwater fish. However, their behavioral patterns differ markedly, due to the influence of the tide.

The Tidal Influence.

Most saltwater species are affected either directly or indirectly by the tide, which raises and decreases shoreline water levels. Tide is caused by the gravitational pull of the moon and the sun. Basically, the water that rushes in and out of bays and estuaries creates strong currents and flushes forage out of cover, which usually triggers fish into feeding.

The tide changes four times every 24 hours: two high tides and two low tides. In most U.S. waters, low tide occurs about six hours after a high tide. And each day, the time of a tide occurs 50 minutes to one hour later than that tide on the previous day. At the culmination of each tide is a slack period, where no water moves.

In chronological order, an incoming tide is called a flood tide. Its peak, about six hours later, is called high-water slack. As the water starts draining out, it is called an ebb tide. About six hours after that is low-water slack, also called dead low tide.

Loose Lines

Arradromous fish—those species that live in salt water but migrate up freshwater rivers lo spawn—survive the change in salinity by dcvelop-thtiiie glands necessary to retain salts.

Fish Recipes

Fish Recipes

This is a great collection of delicious fish and shell fish recipes that you will love.

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