Something Fishy

Something Fishy

   The book, To Sea & Back by Richard Shelton, really shouldn't have been much of a draw for me.  Subtitled, "the Heroic Life of the Atlantic Salmon," I thought, well, a fish is a fish.  Certainly, having seen tuna feed and race with their incredible speed, and sharks, and swirling schools of herring...all were amazing.  But beyond that, I was simply used to seeing salmon as salmon.  They spawn, they head to sea, they return (or struggle to return) and perish;  or they are simply raised on aqua farms;  but basically, there they are almost year-round, nicely fileted, bright pink or red in the cooler case at the store, and ready for the grill.  If that sounds a bit callous, and it does, it was made to sound all the more so after finishing the book.

   Salmon used to be quite plentiful, even filling large rivers such as the Thames and the Danube (pollution drove them away).  And for the most part, they are at sea for over three years, battling everything from larger prey such as dolphins and killer whales to strong currents and changing temperatures.  But what I never paused to consider was the transition they (and like them, sea trout) make from fresh water, to salt water, and back to fresh water.  For us, it would be almost like entering an acidic and sulphur-filled atmosphere, our cells adapting comfortably to it, then returning back to our normal air all after several years.  For the transition, it has to do with phospholipids, a term used to describe cell membranes being charged at one end but not the other; in the case of the salmon, the cell membranes overlap opposite one another.  Okay, too jumbled and too complicated, all this electrical charge stuff...but did you ever think a fish could get too much water (and get waterlogged), or drink water, especially salt water?

   Here's author Shelton's brief description:  Water molecules are small enough to pass through a cell membrane, but those of many of the larger organic compounds such as proteins, carbohydrates and the various amino acids are not.  For a cell bathed in a dilute medium, there is therefore a greater concentration of water molecules outside the membrane than inside.  The result is a tendency for water to flow into the cell, disrupt its chemistry and burst it...this is a constant risk for a salmon in a river because fresh water is much more dilute that the body fluids that bathe its cells.  Although its skin is reasonably waterproof, its gills and the membranes lining its mouth and pharynx are much less so and let in water.  A little water is also drunk, probably mainly involuntarily when swallowing food.  The fish protects its internal fluids from lethal dilution by pumping the excess water out through its kidneys, the long dark red structures at the top of the body cavity that most anglers misinterpret as congealed blood.  Sea water is much more concentrated than the body fluids of a salmon so that when it enters the sea its problem is to conserve water and exclude salts, the exact opposite of what it had to do in fresh water.

   The cells of the salmon also have to change color, their speckled spots in the river (camouflaging them in the gravel beds) "show up horribly against the blue of the ocean."  So the scales start to lay flat and become reflective, hiding them from predators above, while their bellies turn white to hide them from any predators lurking below.  Meanwhile, the scales and gills add age rings or ridges (called circuli), much as trees and shelled animals do and the scent of the river they're departing becomes engrained in their memory (indeed, scientists has purposely displaced salmon nearly a hundred miles away from their birth river, against currents and in higher temperatures, only to find that they often beat the odds and return within a week). 

   To many of you, this might seem a bit too much, all this talk about salmon and fishes and cellular growth.  But the point was to try and display the complexity of even this form of life, the adaptations and evolving that it has to do to survive in its changing environment.  A similar piece appeared in Smithsonian about sea crocodiles by Franz Lidz:  Over the last 70 million years not much has changed in the saltie’s evolutionary design.  This archosaurian behemoth can see well by day and by night and has three pairs of eyelids, one of which functions like swimming goggles to protect the croc’s vision underwater.  Another membrane holds the tongue in place, preventing water from filling the lungs, which is why, even in contempt, the crocodile can’t stick it out.  Salties stalk their quarry with deadly patience—over days if necessary—learning its habits and feeding times...Franklin (a zoologist) and a University of Gothenburg colleague named Michael Axelsson discovered that the saltie has a unique set of valves in its right ventricle that acts as a shunt, diverting oxygen-poor blood away from the lungs and back into the bloodstream.  “The heart valves of most vertebrates are passive and flaplike and function like saloon doors,” Franklin says.  “The croc’s have cog teeth made of nodules of connective tissue.  They look like interlocked human knuckles, and are actively controlled by the nervous system and open and close like elevator doors.  It’s an absolute evolutionary novelty.”  If a crocodile needs to sink in a hurry, it can move its larger internal organs to the back of its body, like a submarine shifting ballast.  Franklin and Axelsson proposed that the cogged-teeth valves allow crocs to ration oxygen underwater and stay submerged for hours...Over the years, researchers have determined that saltwater crocs can hold their breath for nearly seven hours and dive to 23 feet; that they’re capable of walking miles overland between waterholes; that nesting mothers check out potential nests weeks before laying eggs; that dominant males maximize reproductive success, while subordinate males roam hundreds of miles of waterway, possibly in search of unguarded females.

 

   Sometimes, we can overlook life, both above and below us, as "simple" forms of life...an ant or a spider or a chickadee.  But even something far more ancient that our species has much to teach us, its complex organs unique to itself and difficult for us to imagine, much less duplicate.  Life itself is complicated and unique, no matter how simple it might appear...how can a butterfly be so light and yet filled with taste sensors in its feet and be able to travel thousands of miles and back in migration?  Life is full of wonder, and sometimes, perhaps even while staring at a bright red filet of salmon on a bed of ice, we need to be reminded of just how special all life is...and what it took to get here.