What is anadromy?

So what's the skinny on anadromy (pronounced: uh-NAH-droh-mee)? Anadromous fishes are born in fresh water, migrate to salt water for their adult lives, then turn around and migrate back to fresh water to spawn. Salmon are famous for their anadromy and now you can be, too. Just follow these six (not so) easy steps:
Step 1: To the estuary!
Being born is easy--just pop out of the egg and there you are. You've got all the tools you need for breathing and eating. Unfortunately, you're not really strong enough to fight against the flow of the river or stream you find yourself in. Fortunately, the current is taking you exactly where you want to go--to the estuary! Anadromous fishes undertake two (sometimes) long and (always) perilous journeys in their lifetime: from and then back to their spawning grounds.
Striking a balance
We all have salts in our bodies; so do fishes. All fish must adjust to the water around them to keep the salts in their bodies at the right levels.

Freshwater fishes have more salts inside their bodies than there are in the  surrounding water. Water tries to get into the fish to balance the salts. Freshwater fishes never drink; they make a lot of watery urine. They even pump salts into their bodies through their gills. Place your cursor on the freshwater fish to discover how they maintain a good salt balance.

Saltwater fishes have the opposite problem. The salt levels are higher outside the fish than inside the fish. The water in the fish tries to leak out to make the concentrations equal. To fight this, saltwater fishes drink lots of water; make thick, concentrated urine; and pump salts out of their bodies through their gills. Pass your cursor over the saltwater fish below to see how it differs from the freshwater fish.

Anadromous fishes have to switch their strategies before they cross between habitats. Salmon spend time in estuaries, where the water is just a little salty, while their bodies adjust to the new strategy.
Step 2: Make the switch
Freshwater fishes are different from salt- water fishes. Since anadromous fishes start out as freshwater fishes, their bodies must go through changes to become a saltwater fishes. All fishes need to balance the amount of salt in and out of their bodies (see sidebar). If a freshwater salmon swam straight out into the ocean without making those changes, it wouldn't last long. If you want to last out in the big blue then you need to hang out in the estuary and wait for your body to adjust. The estuary is a good place to do it because it is brackish--a little salty, a little fresh.
Step 3: All you can eat!
Once you hit the ocean, it's an all-you-can-eat seafood buffet. Your job is to eat as much as you can as fast as you can. The more you eat, the faster you'll grow, and in the ocean bigger is always better. It means you have fewer predators. The more you eat, the more energy you'll have stored up for the trip back to your spawning grounds and, boy will you ever need it!
Step 4: Find your way back
Some anadromous fishes have amazing homing instincts. Salmon may swim thousands of miles out to sea, but they always find their way back to the exact same stream where they were born. How they do this is not very well known. Trails of bread crumbs would probably just float away or get eaten up by seagulls. So if you're going anadromous, take a map and compass, because this secret of anadromy is only for the salmon. 
Step 5: Switch back
Once you've found you way back to the estuary, don't forget to switch back to being a freshwater fish or your trip back to the spawning grounds will be a short one. You'll also need to stop eating and don your flashy, spawning colors. Hope you ate well out in the ocean, 'cause there are no stops between here and the place of your birth!
Step 6: The long way home
Now for the trip home. No friendly currents this time--it's all upstream. In addition to fighting against the river, you'll also need to contend with fishermen, dams, fish ladders, predators, pollution and more. Once you make it, it's no party either. Females have to dig nests or find spawning sites. Males fight each other for the right to fertilize eggs. After all is said and done, many anadromous fishes die. But their deaths are not in vain--their carcasses feed the stream community, and a rich, healthy community is good for young salmon once they hatch from their eggs. Still want to become anadromous?

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