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Subject: Fish:  The Most Asked Questions
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Fish: The Most-Asked Questions

Being a bouillabaisse of fascinating facts about Fish

The National Marine Fisheries Service annually answers thousands
of questions about the oceans and the life that thrives within
them.  Questions come from seasoned scientists, from teachers,
from elementary school pupils--from a whole host of citizens
seeking knowledge that may be highly specialized, or may be
rudimentary.

On the basis of a canvass of experienced marine scientists in the
Fisheries Service, more than a hundred questions have been chosen
as most representative.  They are the questions asked most
frequently, the topics that people find most interesting.

Marine Finfish and How They Live

Is life found at all depths in the ocean?     
The question was settled in 1960, when Piccard and Walsh reported
a swimming animal, resembling a sole or other flatfish about a
foot long, at 35,800 feet deep, observed from a porthole of the
bathyscaphe, Trieste.  Some scientists believed, as recently as
1860, that marine life could not exist below 1,800 feet. That
view was altered when a telegraph cable laid in the ocean bottom
at 6,000 feet deep was retrieved and found covered with many
forms of marine life.

How many fish species are there?
The most often quoted estimate is 20,000.  There may be as many
as 20,000 more.

Which is the oldest fish, as a class?
The most primitive fish-like animals are those with sucking
mouths, such as lampreys and hagfishes, whose evolution stopped
short of the development of biting jaws.  Mainly bottom-dwellers,
these animals are of great interest to zoologists, for many parts
of their bodies show forms and functions that help to explain
some of the evolutionary steps leading from low to advanced life
forms. 

What is the world's largest fish?  The smallest? 
The largest is the whale shark, which grows to more than 50 feet
in length and may weigh several tons; second largest is the
basking shark, which may measure 35 to 40 feet long.  The
smallest fish is the tiny goby, an inhabitant of fresh-to-
brackish-water lakes in Luzon, Philippines.  It seldom is longer
than a half inch at adulthood, yet is so abundant it supports a
fishery. 

What is the most common fish in the sea?
Any of the several species of Cyclothone, a deepwater fish
sometimes called a "bristlemouth."  Rarely visible at depths that
man can readily reach, the fish is about the size of a small
minnow.  It is netted at 500 meters or deeper all over the world.

What is an anadromous fish?   A catadromous fish?
An anadromous fish, born in fresh water, spends most of its life
in the sea and returns to fresh water to spawn.  Salmon, smelt,
shad, striped bass, and sturgeon are common examples.  A
catadromous fish does the opposite--lives in fresh water and
enters salt water to spawn.  Most of the eels are catadromous.

Why do scientists classify fish?
Since common or colloquial names of fish vary from place to place
(menhaden, for example, are known by at least three different
names, and striped bass are called "stripers"in New England and
"rockfish" in Chesapeake Bay), investigators would have no way of
differentiating among species without a uniform naming system.

The system used to name the 20,000-odd fishes known to science is
called "the binomial system of nomenclature."  It usually
consists of a scientific name in two parts, the generic and
specific names, or three parts if subspecies have been described. 
The words of the names are latinized regardless of the language
or alphabet of the study and are frequently descriptive of a
significant feature of the organism.  The generic name generally
applies to several species showing basic characteristics while a
specific (species) name is based on a few characteristics
applying to one species, separate and distinct from all others.
(Example: The generic name Morone applies to white perch, white
bass, and striped bass; the species names for those three fishes
are Morone americanus, M. chrysops, and M. sexatilis.) 

How is the age of a fish determined?
Mainly by two methods:  Growth "rings" on scales, and/or ringlike
structures found in otoliths (small bones of the inner ear), are
examined and counted.  The rings correspond to seasonal changes
in the environment and can be compared to the annual rings of
tree trunks.  A series of fine rings are laid down in scales for
each year of life--in summer, the rings grow faster and have
relatively wide separations; in winter, slower growth is
indicated by narrow separations between rings.  Each pair of
rings indicates one year. Because scale rings are sometimes
influenced by other factors, scientists often use otoliths, whose
ringlike structures also indicate years of life.

How long do fish live?
A few weeks or months (some of the small reef fishes) to 50 years
or more (sturgeons).  Longevity information is still sparse, but
scientists have learned that species live 10 to 20 years in
temperate waters.

Do some fish give birth to living young?
Yes, many do.  These are called viviparous fishes. The sea
perches of the Pacific coast, for example, give birth to living
young of considerable size, sometimes one-fifth the size of the
mother.  Several kind of sharks produce living young.
Do fish breathe air?
Yes, but not directly into the lungs as mammals do (except for
some tropical fish).  As water passes over a system of extremely
fine g ill membranes, fish absorb the water's oxygen content.
Gills contain a network of fine blood vessels (capillaries) that
take up the oxygen and diffuse it through the membranes.


How do fish swim?  How fast?
Primarily by contracting bands of muscles in sequence on
alternate sides of the body so that the tail is whipped very
rapidly from side to side in a sculling motion. Vertical fins
are used mainly for stabilization.  Paired pectoral and pelvic
fins are used primarily for stability when a fish hovers, but
sometimes may be used to aid rapid forward motion.

Tunas and tuna-like fish, billfish, and certain sharks are the
speed champions, reaching 50 miles per hour in short bursts. 
Sustained swimming speeds generally range from about 5 to 10
miles per hour among strong swimmers.

Can fish swim backwards?
A number can, but usually don't. Those that can are mostly
members of one of the eel families.

Do all fish swim in the horizontal position?
Most do. The sea horse is among the exceptions.  Another is the
shrimp fish of the Indian Ocean, which congregates in schools of
several individuals and swims vertically, its long tube-like
snout pointing directly upward.  A catfish indigenous to the Nile
and other African rivers also swims in the vertical posture. 
Many kinds of midwater deepsea fishes swim or rest vertically.

Do fish chew their food?
Not in the human manner.  Carnivorous fish use their sharp teeth
to seize and hold prey while swallowing it whole or in large
pieces.  Bottom dwellers such as rays are equipped with large
flat teeth that crush the shellfish they consume.  Herbivorous
fish (grazers) often lack jaw teeth, but have tooth-like grinding
mills in their throats, called pharyngeal teeth.  Fish would
suffocate if they tried to chew, or chewing would interfere with
the passage of water over the gills, necessary for obtaining
oxygen.

Can fish distinguish color?
Most fish are color blind, despite the opinion of many sport
fishermen.  Fish can see color shadings, reflected light, shape,
and movement, which probably accounts for the acceptance or
rejection of artificial lures used by fishermen .

Are all fish edible?
Most kinds encountered by anglers are. The organs of some species
are always poisonous to man; other fish can become toxic because
of elements in their diets. The latter are most often from
tropical regions of both the Atlantic and Pacific Oceans.
Scientific literature has pinpointed danger areas in which the
disease called "ciguatera" (a disease dangerous to man) may occur
in tropical and subtropical fish.

How can poisonous fish be distinguished from edible ones?
They cannot, without personal knowledge of the types of fish
which are at times poisonous.  Frequently local customs can be
relied upon.  A comprehensive three-volume publication on the
subject is entitled "Dangerous Marine Animals" by Dr. Bruce
Halstead.

Why do food fish sometimes have a strong odor?
For most species, truly fresh fish is almost odorless.  Fish
begin to smell "fishy" when deterioration sets in, often caused
by incorrect storage practices that bring about the release of
oxidized fats and acids through bacterial and enzymatic action.

Is there much salt in fish?
Very little in most.  More than 240 species contain so little
salt that doctors recommend them in salt-free diets.  Shark meat
is salty--as salty as the sea the shark lives in.

What is the blood like material found along the backbone in the
body cavity of most fishes?
The kidney. It is usually removed when the fish is cleaned.

Can shark meat be used as food for humans?  Is it true that the
meat of the hammerhead shark is poisonous?
Yes to the first question.  Shark meat is palatable and
nutritious if properly prepared.  In some countries shark meat is
marketed under its common name, in others it is marketed under
various names.  The fish in England's "fish and chips" is very
often dogfish (a shark) or school shark.  The prejudice against
shark meat arises from a distaste for the scavenging habits
people attribute to sharks, and to the fact that the meat spoil
quickly. The meat of certain species is apt to be strongly
flavored, a characteristic that may be reduced by icing for 24
hours, then soaking for two hours in brine.  Dry salted shark has
become a staple food in some countries where salt cod was
formerly popular.  But shark liver should never be eaten--its
high concentrations of vitamins can cause illness in humans. It
is only a rumor that the hammerhead is poisonous.


What is the true description of a sardine?
Commercially, the name has come to signify any small herring-like
ocean fish In the United States, it is mandatory that when the
name "sardine" is used on a can, the country or state of origin
be listed, and a statement must appear that identifies preserving
and flavor supplements.

How many kinds of tuna are there and which kind makes up the
biggest catch? 
There are seven commercial and sport-caught tunas, as well as
several related species, all of which are members of what is
called the scombrid family.  Commercially caught tunas consist of
albacore, bigeye, blackfin, bluefin, bonito, skipjack, and
yellowfin. Yellowfin, taken in the eastern Pacific and tropical
Atlantic, makes up the biggest U.S. commercial catch.  Albacore,
caught in the eastern Pacific, is the true "white-meat" tuna;
skipjack, caught throughout the world in tropical and subtropical
waters, makes up the second largest U.S. commercial catch; bigeye
is caught mostly in tropical waters; blackfin is caught
commercially only in the Caribbean and off South America; the
very large bluefin (rod-and-reel record, 1,040 pounds) is a
highly prized sport catch in the Atlantic and Pacific; and the
widely distributed bonito is used largely as pet food.


Do tunas have scales?
Yes, all species do, but scales are so small over most of the
body as to be nearly invisible.  Prominent scaling appears only
around the head, on the cheeks, and in a triangular area on each
side of the body near the head.

Are saltwater catfish good to eat?
The two species of sea catfish caught in U.S. waters are edible.
The gafftopsail catfish is considered more tasty than the smaller
common sea catfish.

What is the fish listed as "scrod" in New England restaurants?
The name comes from a Middle Dutch word "schrode" meaning a strip
or shred. In New England scrod may be immature cod or haddock
weighing 1 1/2 to 2 1/2 pounds.  Sometimes the term is applied to
cusk of about the same weight, or to pollock weighing 1 1/2 to 4
pounds.  When fishermen use the word, they are usually referring
to gutted small haddock.

What are menhaden?
Menhaden are silvery, herring-like fish that travel in large
schools along the Atlantic and Gulf of Mexico coasts of the
United States.  Plankton©eaters, menhaden attain a weight of
about three-quarters of a pound.  Flesh is oily and considered
inedible for humans. The fish are caught by purse-seine nets in
shallow water and processed into oil for cosmetics and fish meal
for animals, particularly for poultry.  Menhaden support the
largest fishery by volume and the eighth most profitable fishery
in the United States.


Where are Atlantic menhaden spawned, where do they go after
hatching?
Spawning is in the ocean.  One important spawning site is at
Onslow Bay, North Carolina.  Some spawning takes place along the
Atlantic coast from Massachusetts to Florida.  The young menhaden
first drifts with currents until it reaches an inlet, then works
upstream to live for the summer near freshwater.  In fall,
schools move downstream to permanent ocean residence.
What do herring eat?
They subsist on zooplankton. Herring, which populate the oceans
in enormous numbers,play an important role in the oceanic food
chain in that they are primary converters of plankton. Herring
form the food base for many larger species, and enormous
quantities are taken commercially for fish meal, human food, and
bait.

Are the eyes of flatfishes on the right or left side?
Except for the rare abnormal specimen, two of the four flatfish
families (tongue soles and turbots) are always sinistral (eyes on
the left side); the other two (both flounders) are dextral (eyes
on the right œside)

Has any kind of marine or ocean dwelling fish been successfully
transplanted from coast to coast in the United States?
Yes, larvae and juveniles of the shad and the striped bass were
taken from the Atlantic and released in the Pacific in the
l870's. So successful were the transplants that shad became
permanent inhabitants of waters from southeast Alaska to Los
Angeles, and striped bass support a good sport fishery off the
California and Oregon coast.

How large do ocean sunfish get?
All four species reach from seven to ten feet in length.  Because
of their tremendous weight, the fish are difficult to land and
weigh.  One accurately weighed specimen tipped the scales at
3,102 pounds.


How do porcupine fish inflate themselves?
All puffer-like fish inflate by pumping water into special sacs
when in their natural environment.  Out of water, a puffer fills
the sacs with air instead, and takes on a balloon-like
appearance.

What is an "exotic" fish?
One not native to an area, but introduced either by accident or
design.  Some such species can cause problems.  Often their
natural predators are absent from the new area, permitting more
rapid reproduction rates than those of natural inhabitants,
sometimes at the expense of more desirable native fish.  The
"walking catfish" in Florida is an example.  Thought to have
escaped from a private aquarium, the catfish have shown a
remarkable ability to avoid eradication efforts by man.  An
aggressive and voracious fish, it poses a threat to other forms
of aquatic life. Population is now estimated in the millions.

What fishes are named after other animals?
Many are named after animals--alligator, bird, boar, buffalo,
cat, cow, dog, elephant, frog, goat, goose, hawk, horse, leopard,
lizard, parrot, porcupine, rabbit, sheep, squirrel, tiger, toad,
unicorn, viper, wolf, and zebra.

What kind of fish is a "Bombay Duck"?
Also called bummalo, Bombay Duck is a marine lizardfish from
southern Asia, particularly abundant in the Ganges Delta and the
Arabian Sea of western India.  The ordinarily small fish is
split, boned, and sun-dried, and used as a condiment.


How much electricity does an electric eel generate?
The average discharge is more than 350 volts, but discharges as
high as 650 volts have been measured.  Voltage increase until the
eel is about three feet long, after which only amperage
increases.  Some South American eels measure 10 feet in length.

What are moray eels and where are they found?
Moray eels belong to a family of fish which differs from the
common eels by their lack of side fins, their well-developed
teeth, and their lack of scales.  Common eels have embedded
scales, but these are not readily noticeable.

Morays occur in tropical and subtropical seas of the world. In
the United States, they are usually found in quantity only in
Florida waters, although they have been seen as far north as
North Carolina and even New Jersey.  Little is known of their
breeding habits except that the young pass through a stage which
is very thin, ribbon like, and transparent.  Morays feed largely
on other fish caught as they work their way through coral reefs.
Some morays are equipped with teeth in the back of the mouth for
crushing hard-shelled animals such as clams and oysters.

Morays are occasionally caught on hook and line by fishermen,
sometimes are captured by trawlers that drag nets over the
bottom.  People in some parts of the world value the moray as
food.

Some Pacific morays measure as long as 10 feet and are considered
dangerous to man when aggressions are aroused, generally by
divers' actions.  Several records exist of attacks on humans by
wounded morays.

What is pearl essence?
It is the silvery substance in the skin of herring and other
fishes.  Pearl essence is a lucrative byproduct of herring
fisheries inasmuch as it is essential to the manufacture of
lipstick, nail polish, paints, ceramics, and costume jewelry.

Is the blue shark really blue?
In life the blue shark displays a brilliant blue color on the
upper portion of its body and is normally snowy white beneath.
The blue quickly fades to dull grey after the shark is killed.
The mako and porbeagle sharks also exhibit a blue coloration, but
it is not nearly as brilliant as that of a blue shark.  In life
most sharks are brown, olive, or grayish.

What attracts sharks?  Which are most dangerous?
Considerable research has been devoted to finding out what
stimuli attract sharks and incite them to attack.  Results are
mostly inconclusive, but some general principles have been
advanced: Certain types of irregular sounds--like those made by a
swimmer in trouble or a damaged fish--seem to attract sharks from
great distances.  Sound, rather than sight or smell, seems to be
a shark's primary cue for moving into an area.  Some scientific
experiments indicate that sharks can distinguish light colors
from dark, and that they may even be able to distinguish colors.
Yellow, white, and silver seem to attract sharks.  Many divers
maintain that clothing, fins, and tanks should be painted in dull
colors to avoid shark attacks.

Though blood itself may not attract sharks, its presence in
combination with other unusual factors will excite the animals
and make them more prone to attack.

The most dangerous species in order of documented attack records
are: the great white shark, bull shark, tiger shark, grey nurse
shark, lemon shark, blue shark, whaler shark, sand tiger, several
species of hammerheads, and the mako.  Some species such as the
nurse shark are extremely sluggish and have poorly developed
teeth, but even these have been known to attack man when excited
or disturbed.

What sea creatures other than sharks may be dangerous to
swimmers?
The barracuda (though divers claim its ferocious reputation is
undeserved), moray eels, octopuses, and sharp-spined sea urchins
can be dangerous to swimmers.  The Portuguese man-of-war has
tentacles up to 50 feet long with specialized cells that produce
painful stings and welts on contact by swimmers.  Sting rays,
toadfish, catfish, and jellyfish can inflict damage on swimmers
and waders.  Certain coral-reef organisms are to be avoided by
divers.

How many species of Pacific salmon are there?
There are six: Chinook, coho, pink, sockeye, chum, and masu.  The
first five are found in North America.  The masu occurs only on
the Asiatic coast of the North Pacific.

Is it true that salmon return to spawn in freshwater areas where
they were born?
Almost always.  Some straying has been documented, but it is
minor.  Most spawning salmon return to the precise stream of
their birth, sometimes overcoming great distances and hazardous
river conditions to reach home.

What is the difference between the Atlantic salmon and the
Pacific salmon?
The Atlantic salmon is actually a member of the genus Salmo, or
trout family, not a salmon, which is placed in the genus
Oncorhynchus.  The misnomer is so widely accepted that it would
only cause confusion to rename the species.  The main biological
difference between the Atlantic and Pacific "salmons" is that
Salmo may spawn more than once, and Oncorhynchus die soon after
one spawn. 

Where do salmon go in the ocean?
Contrary to earlier beliefs, many salmon from North American
rivers roam far at sea in the North Pacific Ocean and the Bering
Sea.  The oceanic distribution of the salmon is dependent upon
the species and point of origin.  Sockeye and chinook salmon from
northwest Alaska, for example, may migrate across the Bering Sea
to areas close to Kamchatka, U.S.S.R., and south of the Aleutian
Islands into the North Pacific Ocean; the sockeye also migrate
eastward to the Gulf of Alaska.  Salmon such as the pink, chum,
and coho from central and southeast Alaska, British Columbia, and
Washington State, migrate out into the northeastern Pacific and
Gulf of Alaska.  Many steelhead trout from Washington and Oregon
are known to migrate far at sea to areas off the Alaskan
Peninsula.  Some salmon migrate several thousand miles from the
time they leave the rivers as juveniles until they return as
adults.  A chinook salmon tagged in the central Aleutian Islands
and recovered a year later in the Salmon River, Idaho, had
traveled about 3,500 miles; a steelhead trout tagged south of
Kiska Island (western Aleutians) was recovered about six months
and 2,200 miles later in the Wynoochee River, Washington.

What is a kokanee, or silver trout?
It is the landlocked subspecies of a sockeye salmon.  The kokanee
spends its entire life in fresh water and usually does not attain
the size of its sea-migrating cousin.

Do landlocked Pacific salmon die after spawning?
Yes.  This phase of their life history is the same as their 
seagoing relatives.

How large do salmon get?
Weights of 100 pounds and slightly over have been reported from
European countries for the Atlantic salmon; the record for the
largest of the Pacific species, chinook, is 126 pounds for a fish
caught on commercial gear in Alaskan waters.

What is the oldest known age of salmon and steelhead (in
completed years)?
Pacific salmon: chinook--7; sockeye--7; silver--4; chum--6; pink-
--2.  Atlantic salmon: 8, Steelhead trout: 8.

Is a steelhead a salmon or a trout?
The steelhead is a rainbow trout that migrates to sea as a
juvenile and returns to freshwater as an adult to spawn.  Unlike
the Pacific salmon, the steelhead trout does not always die
following spawning and may spawn more than once and return to the
sea after each spawning.

How old are salmon when they migrate from fresh water to the
ocean?
That depends on species:
Chinook--fall chinook, 3-4 months after hatch; spring chinook,
12-16 months; Coho--12-24 months; Chum--a week to a month;
Sockeye--12 months to 36 months; Pink--a week to a month.

How many eggs do salmon have?
Generally from 2,500 to 7,000 depending on species and size of
fish.  The chinook salmon generally produces the most and largest
eggs.

What are salmon fed in a hatchery?
Vitamin-rich, high-protein diets made up of dried meals from
coarse fish, animal meat excess, plant meal and bone meal, or
meal from calcium-rich shells.

How many of the young salmon released from hatcheries come back
as adults?
Releases of large fingerlings usually result in returns of one to
five percent.

Why are fishladders constructed?
A fishladder, or fishway, often used in salmon country, is
constructed to provide for upstream passage of fish over a dam or
a natural barrier that might prevent or impede progress to
spawning grounds.

How can I maintain a small saltwater aquarium?
Three principal rules must be followed:
(l) Keep it clean.  Remove excess food, coral, algae, and
miscellaneous debris.  Omit over-decoration with coral, sponges,
and other marine plants.  Marine aquariums are vulnerable to
pollution by spoiled food.
(2) Stock sparingly, using no more than a single one-inch-long
fish per gallon of water capacity.
(3) Use quartz sand on a sub-sand filter in the bottom of the
aquarium.  Good filtration is vital.  In addition, some
monitoring of fish behavior is advisable--fin-nipping, for
instance, may be a sign of problems.  Consult literature for
precise information.


Shellfish and Other Invertebrates

How many kinds of lobsters are there in this country, and why are
different varieties called lobster?
Two kinds of lobster-like crustaceans exist United States waters.
The "true" lobster (the American lobster) is designated as such
to differentiate it from the other form found  here, the spiny
lobster.  The two, from different families, display two
differences: The true lobster has claws on the first four legs,
lacking in the spiny lobster; the spiny lobster has a pair of
horns above the eyes, lacking in the true lobster.  To avoid
confusion over common names, it is best to call the true lobster
the "American lobster," and the spiny lobster just that.  The
item marketed as "lobster tail" usually is a spiny lobster.  The
spiny lobster is found in warm waters off Florida, in the West
Indies, and off southern California.  Record weight for the
American lobster is 45 pounds.

Does the deepwater northern lobster population differ from that
found just off the coast?
The species in each population are identical in all respects.

How far do lobsters travel?
Inshore lobsters tend to stay in one place, seldom moving more
than a mile or so, but deepwater lobsters farther out on the
Continental Shelf follow a seasonal migratory pattern shoreward
in summer, returning to the Shelf again in the autumn.  The
record travel so far is 225 miles covered by a lobster tagged off
the Continental Shelf and recovered at Port Jefferson, Long
Island, New York.

What does a lobster eat?
Mussels, crabs, clams, and seaworms, as well as dead fish.

What color is a lobster's blood?
Colorless.  When exposed to oxygen, it develops a bluish color.

What is "tomalley"?
Tomalley is the lobster's liver.  It turns green when cooked and
is considered a delicacy.

What is the coral colored material often seen in a cooked
lobster?
Coral is the egg mass of a female lobster.  Cooking colors the
tiny eggs a deep coral or red.

How does a lobster grow?
It sheds its hard shell and grows a new, larger one.  Since the
skeleton is on the outside, this molting is essential to growth.

How many times must a lobster molt before it reaches market size?
Between 20 and 30 molts take place before a lobster reaches the
one©pound market size.

How old is a one©pound lobster?
No one knows exactly, but aquarium studies suggest 5 to 7 years.

How many one©pound lobsters are needed for a pound of lobster
meat?
Five, on the average.

How long can a lobster live out of water?
Several days if kept in a cool, moist environment.  The lobster
is a gill-breather, and moisture is essential to survival.

Can a lobster be kept alive in fresh water with ice?
No.  Fresh water is lethal to a lobster. The animal has salty
blood and tissue, which re­quire a seawater environment if life
is to be maintained.

Why does a lobster turn red when cooked?
The red pigment is the most stable component of the coloring in a
lobster shell.  The greens and browns which darken the shell in a
live lobster are destroyed by cooking.

How can one tell if a boiled lobster was alive when cooked?ûû
Upon the death of a lobster the tail loses its elasticity and 
ability to curl under the body.  When plunged into boiling water, 
a live lobster curls its tail under.  It remains in that position
during and after cooking.

Have people been poisoned by eating lobsters that were allowed to
die before being cooked?  Is it true that a dead lobster
deteriorates very rapidly? What happens when a live lobster is
frozen?
Lobsters are not poisonous if they die before cooking, but  
cooking should not be delayed.  Many lobsters sold commercially
are killed and frozen before cooking.  Lobsters and other
crustaceans do spoil rapidly after death, which is why many
buyers insist on receiving them alive.  If the lobster is
"headed" before or soon after death, the body meat will keep
fresh longer. This is because the so-called head includes the
thorax, the site of most of the viscera and gills, which spoil
much more rapidly than claw or tail meat.  Freezing slows
deteriorative changes and harmful chemical actions that follow
death.

Is it possible to raise lobsters on a commercial basis?
Not yet, but research is underway to develop rearing techniques
and to assess the economic feasibility of rearing the American
lobster commercially.  In the opinion of many scientists working
with the American lobster, commercial aquaculture can be achieved
in the near future with a sufficient level of effort.  Future
projections for the culture of the spiny lobster are not,
however, optimistic.  Unlike the American lobster which has a
relatively short larval life (several weeks), the spiny lobster
has a larval life of about six or seven months. The technical
difficulties presented by the fragile, demanding requirements of
the early life stages discount the use of traditional hatchery
methods with any degree of success or practicality.

Have Maine lobsters been successfully transplanted to the west
coast?
Attempts have been made to do so, but success has been limited.
The Canadian government discontinued in mid-1973 a six-year-old
experiment in which the lobsters were reared successfully in the
waters off British Columbia.  The decision to drop the project
was evidently dictated by economics.

I've heard that lobsters molt, but I've never seen a cast-off
shell.  Why?
Lobsters often eat the cast-off shell to regain needed minerals.

Can crabs swim?
Most crabs "walk" or run across the ocean bottom.  Some, such as
the commercially caught blue crab of the Atlantic coast (a member
of the one family of "swimming crabs") can swim.  Their rearmost
pair of legs is modified for swimming and legs are paddle shaped.

How do crabs grow?
By shedding their outgrown shell. The rigid shell imprisons the
crab and limits growth.  Once the shell is shed, the crab can
absorb water and expand into its new grown shell.

How much does a blue crab increase in size on molting?
Under normal conditions, about a one-third increase occurs with
each molt.

What is the difference between soft© and hard­shell crabs?
They are the same species.  A soft-shell crab is one that has
just discarded its shell. Crabs which have just shed their shell
hide in rocks or bury themselves in sand and mud to escape
predators. They emerge after the new shell hardens, a quick
process.

How old does a blue crab get?
A female may live 2 years, a male 3.

What is a "coconut crab"?  Where do they live?
A large, land hermit crab, which lives on tropical Pacific
islands. The crab is so named because it eats coconuts, is even
caught on coconut used as bait. The meat is considered a delicacy
in the islands.

Is a stone crab harmed when its large claw is broken off?
Fisherman often break off the large claw and throw the crab back
into the water.  If the break is made at the first joint, the
crab is not harmed.  The stone crab can and does sever its own
claw at the first joint (by muscular contraction) to escape from
danger.

What are the small crabs found inside oysters?  Are they harmful
to oysters?  May humans eat them?
These are "pea" crabs.  They live, often in pairs, inside the
oyster shell, eating food collected on mucous strands in the
oyster.  Because they do cause damage to oyster mantle and gills,
the crabs are considered parasites.  Pea crabs are not harmful to
man.

How do prawns, crayfish, and shrimp differ?
As so often happens, common names are used loosely and
inconsistently in the shrimp family.  The "prawn" of Great
Britain and other countries is essentially the same animal as the
shrimp of the United States.   In this country, the term "shrimp"
applies to all crustaceans of the Natantia group, regardless of
size.  "Crayfish" or "crawfish" are names given to both a common
freshwater crustacean and to the saltwater spiny lobster.

Is there more than one kind of shrimp?
Numerous varieties exist, among them brown, white, pink, royal
red, brine, and rock shrimp.

How big do shrimp grow?
Depending on the species, size ranges from about 1/2 inch long on
the west coast of the United States, to almost 12 inches
elsewhere.

How long do shrimp live?
The life cycle varies geographically and by species.  Some live
as long as 6 1/2 years, others live only a year.

How many eggs does a shrimp produce in one spawning?
About 500,000.

How much shrimp is produced in the United States, and where is
the largest catch taken?
The annual catch has been running close to 400 million pounds for
several years.  The Gulf States usually lead in shrimp catches,
with Texas and Louisiana the leading States.  Alaska has been an
important shrimp producer for the past several years.  The shrimp
fishery has the highest market value of all U.S. fisheries.

What are the commercially important shrimp on the east coast of
the United States, and what are their ranges?
Three shrimp species are of primary commercial importance: Pink
shrimp from Chesapeake Bay through the Gulf of Mexico and the
West Indies to Brazil; white shrimp from Fire Island, New York,
to Cape Kennedy, Florida, in the Gulf of Mexico from Pensacola,
Florida, to Campeche, Mexico, in Cuba and Jamaica; brown shrimp
from Massachusetts down the east coast through the Gulf of
Mexico, and the West Indies to Uruguay.

What is the biggest bivalve mollusk, cephalopod mollusk, and
crustacean known to man?
The biggest bivalve mollusk is the clam Tridacna, native to the
Indo-Pacific, which reaches a weight of 500 pounds.  The giant
squid, nearly sixty feet long, is the biggest cephalopod.  The
Alaskan king crab is the largest of the crustaceans, weighing up
to 15 pounds, and measuring four to five feet across shell and
claws.

What do oysters and clams eat?
Called filter feeders, oysters and clams eat plankton.  By
pumping water through their bodies, the mollusks strain the
microscopic organisms through their gills, which act as sieves.

Clams seem to squirt water through their siphons.  What purpose
does the siphon serve?
Three main purposes: breathing, obtaining food, and eliminating
waste products.  Since clams are relatively immobile and movement
is usually limited to burrowing in the sand, their double-tubed
siphon--which operates much like a snorkel--is their lifeline.
Inflowing water is pumped through the siphon, passed over the
gills, and strained to remove food particles.  After receiving
carbon dioxide from the gills and other waste products from the
digestive tract, the water is expelled through the outgoing
siphon.  Constant circulation of the water is maintained by the
beating of a multitude of microscopic hairs (called cilia)
located inside the tube and in the gill chamber.

What causes a reddish color in the liquor of shucked oysters and
clams?
The red algae they sometimes consume, often composed of the
microscopic one-celled dino-flagellates which appear in
planktonic mass.

How does a clam shell grow?
A thin tissue that adheres to the inner surfaces of the shell,
called the mantle, and a thickened rim of muscular tissue at the
mantle edge deposit new shell material at the shell edge. Rings
on the shell indicate how many years old a clam may be.

How do clams establish themselves on the sea bottom?
Certain kinds of clams, in early stages of life possess a gland
that produces a thread-like material (byssus) that serves to
anchor them to grains of sand or rocks.  Other types of clams
lack a byssal gland and use the foot to burrow into the seabed.
As the clam grows, its wedge-shaped foot, which expands and
contracts as it moves, becomes more important as a burrowing
tool.

How do clams reproduce?
Eggs and sperm are released into the water seasonally, generally
in mid-summer when water is warm and planktonic food is abundant. 
After fertilization of an egg, cellular division produces larvae
and eventually tiny clams that settle to the bottom.  In a few
species, the larval stage is completed within the mantle cavity
of the parent.

Which of the clam species is of greatest commercial importance to
the United States, where is it fished, and what quantities are
landed?
The oceanic surf clam is the most important commercial species.
The largest clam of the U.S. east coast, it sometimes reaches a
shell length of more than eight inches.  Landings of surf clams
in New Jersey and Virginia account for about half the total U.S.
annual landings of all clam species.  The surf-clam catch in
recent years--in shucked meats--ranged from about 41 to 63
million pounds.

How are soft-shell clams harvested?
They are dug from the intertidal flats of bays and estuaries at
low tide in New England, using a short-handled fork to obtain
clams living in burrows six to ten inches below the surface.  In
Chesapeake Bay, because the beds are mostly subtidal, a hydraulic
dredge washes clams from the bottom and onto an endless belt that
conveys the clams to the dredge boat.

How are hard©shell clams harvested?
Long-handled tongs, rakes, and small dredges operated from small
skiffs in shallow subtidal zones of bays and estuaries.  The
larger hydraulic escalator dredge is used for hard-shell clams as
well as soft-shells.

How are surf clams caught?
A large (about 1 1/2©ton) hydraulic dredge washes clams off the
bottom and carries them aboard 60- to 100-foot vessels.

What is the biggest clam caught and eaten in the United States?
The geoduck (pronounced gooey©duck) clam caught in Northwest
Pacific waters, weighs an average three pounds and yields over a
pound of flavorful meat.  Now sold commercially, geoduck clam
meat can be used in minced form or in steaks.

What kinds of predators attack clams and oysters?
Man, water birds, rays, starfish, whelks, drills, and sponges,
among others.

How do oysters produce pearls?
Pearls begin with the presence of a foreign substance, such as a
grain of sand, that lodges in the shell.  The oyster's body
reacts by depositing layers of nacreous (pearl like) material
around the foreign body to wall it off and reduce irritation.

Do all oysters produce pearls?
Many oysters--as well as some clams and mussels--manufacture
material like the pearl producing substance.  True pearl-
producing oysters, however, inhabit waters of the Indo-Pacific.

Is it safe to eat oysters during the months without R's?
Yes.  Fresh oysters properly refrigerated are wholesome and
nutritious throughout the year.  They spoil rapidly at high
temperatures, however.  The belief that oysters were unsafe to
eat in May through August arose in earlier days when
refrigeration was less prevalent than it is today.

How does a scallop move?
It compresses the valves of its shell and forces water backward
in jets near the shell hinge. The force drives the scallop in the
direction of the shell opening.  The bivalve appears to be
clapping the two sides of its shell together.

Are any snails commercially caught for food off the coasts of the
United States?
The most commonly eaten snails in this country are the abalone,
caught in the waters off California, and various conchs from
Atlantic waters.


What purpose do the holes along the edge of an abalone shell
serve?
Internal gills discharge water through the holes, as part of an
abalone's respiratory process.

What are oyster borers?
An oyster borer, or drill, is an aquatic snail that preys on
oysters, especially thin-shelled young oysters.  Using a band of
scraping teeth (a radula) and a shell-dissolving secretion, the
gastropod drills a hole in the oyster shell and eats the creature
within.

Are there any poisonous marine snails?
Yes. Cone shells (family Conidae) include members with toxic
venom.  These mostly tropical forms can be highly toxic, even
fatal, to man.  Their poison is injected by a spear-shaped rod
called a radula.

What is the sand collar that one often sees on beaches at low
tide?
A sand collar is the egg case made by moonsnails, of the family
Naticidae.  The eggs are laid in a gelatin-like matrix with which
sand grains are mixed. The individual egg capsules can be seen
under a magnifying glass or microscope.  When the little snails
hatch, they swim around for a while before settling on the
bottom.

What is chitin?
The structural material that forms the shells of crustacea, such
as crab, shrimp, and lobster.

How does the consumer know that shellfish are safe to eat?
Clams and oysters in the shell should be alive and the shells
should be closed tightly or should close when the mollusks are
tapped.  The U.S. Public Health Service, in cooperation with the
States, has a sanitation control program that covers the labeling
and shipment of clams, mussels, and oysters.  These shellfish may
be harvested only from non-polluted waters and processed for
shipment in sanitary plants inspected by State shellfish
inspectors.  Authorities periodically test water for sewage
pollution and ban catches from polluted areas.

How unsafe are shellfish from polluted waters?
They are dangerous to man, causing mild to severe illness,
sometimes death.  Both sewage and industrial wastes can affect
shellfish.

Will cooking make sewage-polluted shellfish safe to eat?
Not entirely.  Cooking will kill bacteria that cause some
diseases, but it is not known whether certain virus diseases,
such as infectious hepatitis, can be prevented by cooking.

Is it possible to purify shellfish from sewage-polluted water for
safe eating?
Yes.  Sewage-polluted shellfish transplanted to clean water
purify themselves rapidly and become safe to eat.

Do shellfish contain mercury levels dangerous to man's health?
No.  Tests of shellfish to date have shown mercury levels to be
below those considered dangerous to humans.