When I was ten, I carried a tin can of worms and a battered
fishing rod to the wild shores of Brickyard Pond, in the woods
behind our subdivision. We caught mostly scrappy sunfish and white
perch, with the occasional bass thrown in. There were alewives in
some of the brooks, too, and we caught them with nets. As for the
pretty trout that came from the hatchery truck, I never caught one.
The fish I caught were mostly round, dark green or gray, and
mottled like the mud and sand bottom of the pond.
Then one day a friend's older brother, a real fisherman with a
green fishing vest, caught a large brown trout. I couldn't believe
my eyes. The fish, shaped like a torpedo, was a yellowish gold and
it had big red spots on its sides. Years later, I caught my first
brook trout on a fly rod at Shoal Pond in the White Mountains.
Again, I was mesmerized by the intense colors: the yellow and red
spots, some with bluish halos, the fins that were bright red with
white and black trim.
It all begs the question: why the trout's fancy colors when so
many other fish are dishwater dull?
Part of the answer can be found in the biological record. Trout
are part of the salmon family, which diverged from other bony
fishes at the end of the Oligocene, about 30 million years ago.
This was a time of global cooling, which suited the trout just
fine. They were coldwater pioneers, who pushed into higher
elevation watersheds to spawn and sometimes reside. Brook trout,
our native trout, are part of the char genus (Salvelinus) and among
the most cold-tolerant fish, able to live in glacial meltwater and
isolated mountain lakes that stay frozen much of the year. As the
last glacier melted and receded from the Northeast - about 10,000
years ago - brook trout migrated along the edge of the retreating
ice, occupying enormous glacial bays, dammed glacial lakes, and
northern rivers and streams.
Where the water is clear and cold, bright colors can be seen.
There is an advantage to this. Trout are territorial, and males and
females aggressively defend feeding stations. They flash their
colors in lateral and frontal threat displays, and if that doesn't
work to push off an intruder, they nip and chase each other to
defend their position in a stream.
Color and pigment patterns seem to matter during fall spawning,
too. The fins and bellies of brook trout, like the maple leaves
above, turn orange in the fall. While shortened day length triggers
spawning behavior, it's the trout's heightened color that brings on
the aggression as males vie for the opportunity to be closest to an
egg-laying female. The largest, most brightly colored males will
most effectively fend off the peripheral males. These males are not
just rivals, they also cannibalize the eggs.
Bright color can be a disadvantage, of course, especially to an
animal that must be constantly wary of predation from above. So
trout have evolved a two-toned skin. The bright threatening flash
of their silvery sides - in rainbow trout the silver is
superimposed by a brushwork of red - contrasts with a dark back,
engraved with ornate markings called vermiculations. These speckled
patterns break up reflected light, merging trout with the gravely
substrate below. In moving water, trout are nearly invisible from
Environmental factors also influence a trout's colors. Food
supply, for example, can have a major effect. Whether a brook trout
has a pale or a pink belly is partly a function of how many
crustaceans - small crayfish and shrimp -it eats. Brook trout that
spend part of the year in the ocean take on a bluish hue, while
trout living in the acidified waters of isolated beaver ponds are
often deep yellow, closer to the tannin leachates that turn such
waters brown. Chemical pollution may influence trout pigmentation,
Chemicals found in certain anti-fouling-boat-bottom-paint turn
rainbow trout paler. Hybridization adds to the puzzle of fish
pigmentation. The High Sierra's golden trout, arguably the
prettiest trout in the world, hybridize with west slope cutthroats
to make a fish that fishermen call "cutgolds." The fact that we've
been busy introducing trout to waters everywhere since the 1850s
muddies the color palette even more.
Looks can be deceiving, and maybe we put too much stock in
beauty. But there's an ecological lesson in a trout's good looks.
These fish are decked out in sky, sunshine, and the multi-hued
gravels of the places they call home. They're a sentinel species:
as goes the cold, clean water, so go the trout.
Tim Traver is the author of Sippewissett, published by Chelsea
Green. The illustration for this column was drawn by
Adelaide Tyrol. The Outside Story is assigned and edited by
Northern Woodlands magazine and sponsored by the Wellborn Ecology
Fund of New Hampshire Charitable
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