Ken Schultz's Field Guide to Saltwater Fish - Macaw Pets store

A winter fishkill occurs when ice and
snow cut off the transfer of oxygen from
the air to the water; the oxygen in the
water gets used up, and fish die. This
does not happen if there is enough oxygen
in the water to last throughout the
winter until the ice and snow melt.
A summer fishkill usually occurs
when inadequate amounts of oxygen
exist in the water during extended periods
of hot, calm, and cloudy days. Warm
summer water temperatures, high
demands for oxygen, and days with no
sunlight or wind to mix the surface
water may lead to oxygen demands
exceeding oxygen production. When
this happens, distressed fish may be seen
as they rise to the surface and gasp for
oxygen, and dead fish may be seen floating
on the surface.
FLATFISH
The term “flatfish” broadly refers to a
group of more than 500 species of
unique, compressed fish that have developed
special features for living on the
bottom, the most interesting of which is
that both eyes are on one side of the
head. They are capable of excellent camouflaging
and are widespread, ranging
from cold, boreal habitats to warm, tropical
environments. The flatfish group
includes some of the world’s most important
commercial, recreational, and food
fish, such as sole, flounder, halibut, dab,
plaice, and turbot—names that often
apply to species in different families.
FRESHWATER
Water with less than 0.5 gram per liter of
total dissolved mineral salts.
GILL
A breathing organ with much-divided
thin-walled filaments for extracting oxygen
from the water. In a living fish, the
gills are bright red feathery organs that
are located on bony arches and are
prominent when the gill covers of the
fish are lifted.
GILL RAKERS
Toothlike extensions, located along the
anterior margin of the gill arch, that
270 Glossary
project over the throat opening and
strain water that is passed over the gills.
These protect the gill filaments and, in
some fishes, are used to sieve out tiny
food organisms. The number of gill rakers
on the first gill arch is sometimes
used as an aid in identifying or separating
species that closely resemble one
another.
GRILSE
A salmon, usually male, that returns to
freshwater rivers after 1 year at sea.
These are small fish, generally weighing
from 2 to 4 pounds.
GROUNDFISH
A species or a group of fish that lives
most of its life on or near the seabed.
The term may be used synonymously
with demersal. Groundfish refers to
Atlantic cod, haddock, pollock, American
plaice, white hake, redfish, and various
flounders.
HYBRID
The offspring of two individuals of different
species. The offspring of two individuals
belonging to different subspecies of
the same species are not hybrids.
Hybridization may occur in the wild
or under artificial conditions. Some
species that have been known to crossbreed
naturally, although not frequently,
include lake trout and brook trout
(splake), northern pike and muskellunge
(tiger muskie), and walleye and sauger
(saugeye). Hybrid fish have been cultivated
in hatcheries by fisheries managers
for stocking purposes; hybrid striped
bass (known as whiterock bass, wiper,
and sunshine bass), which result from a
cross of pure-strain striped bass and
white bass, have been extremely popular
for stocking and are widely spread in
freshwater lakes and reservoirs. Most
hybrid fish are sterile (although some,
like whiterock bass, are not), so the
stocking of these fish is attractive
because they can be controlled fairly
well; if the initial stocking experiment
does not achieve the desired results, the
population of hybrids can be extinguished
by discontinuing stocking.