The Anatomy and Species of Fish
W
HEN YOU THINK of animal production or crop pro-
duction in the agricultural industry, do you
also think of aquatics? Probably not. However, in reality, aquaculture is one of
the fastest-growing industries in the
agricultural sector of the United States.
Throughout this E-unit, we will explore
the key concepts and aquacrops that
contribute to the U.S. seafood industry and agricultural realm, as well as enhance the environment.
Objectives:
þ
1. Describe the aquaculture industry.
2. Describe the anatomy of a fish.
3. Identify the major species of fish and other aquatic animals used in
aquaculture production.
Key Terms:
Ñ
aquacrop
aquaculture
brackish water
crustaceans
fingerling
fish
fresh water
fry
gills
hatcheries
prawn
salt water
spawning
The Aquatic Industry
Aquaculture is the production of aquatic animals and vegetation. For top-quality production, aquaculturists, just like other agricultural producers, must ensure proper management
and nutrition and pay attention to environmental concerns. In North America, most
aquaculture centers on the production of aquatic animals, such as fish and crustaceans, like
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shrimp and lobster. However, globally, aquaculture embraces a wider variety of aquacrops. An
aquacrop is a commercially produced water species. Aquacrops are produced for several purposes, such as human food, ornamental fish, bait, feed for other aquatic organisms, and recreational sport fishing.
Aquacrops can differ greatly between areas because of variations in climate, water type,
environmental conditions, and even consumer demand. For example, there are three distinct
types of water: fresh water, salt water, and brackish water. Fresh water is water that contains
little or no salt and is commonly inhabited by trout or bass. Salt water is water that contains
more than 16.5 parts per thousand of salt and is home to salmon and red fish. Brackish
water is a mixture of both fresh water and salt water. Crab and mullet are key examples of
aquacrops raised in this type of water.
Animals that have gills instead of lungs are called fish. Fish are vertebrates (i.e., they have
backbones). A fry is a newly hatched fish, and a fingerling is an immature fish that is between
the stage of a fry and a stock fish.
From managing aquacrops, producers in the aquaculture industry have developed hatcheries that facilitate the incubation and artificial hatching of fish eggs.
In addition, six requirements must be met for the production of a quality aquacrop:
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The producer must ensure that a market exists for the product. An aquatic business will
be a failure before it begins unless there is a strong consumer demand for the aquacrop
produced.
The producer must select a species suited to the area and growing conditions. If the species’ requirements are not in tune with the growing conditions available, production of
that species will be very limited.
The producer must provide the species with a quality water source that meets its requirements. For example, if the species needs a warm saltwater environment, a source of warm
salt water must be provided. If, instead, the producer provides a source of cool salt water,
the result will be a massive failure of production.
The producer must consider the nutritional needs of the aquacrop. An aquatic animal is
very specific in the feed it can digest. If the producer provides an incorrect-sized pellet or
improper nutrition, the production of the animal will be limited and the chance for disease will be increased.
The producer must evaluate diseases and illnesses and use proper control measures.
The producer must manage the oxygen level and chemical balance of the water.
The Anatomy of a Fish
The anatomy of a fish is divided into two categories: internal and external.
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INTERNAL ANATOMY
A fish has the same internal systems as other vertebrates—nervous system, circulatory system, sensory system, skeletal system, muscular system, respiratory system, reproductive system, and digestive system.
In an aquatic species, the nervous system consists of the brain and the spinal cord. Messages
are sent through the system’s spinal nerves.
The circulatory system of a fish focuses on the heart and the blood vessels. The system, as
in other species, contains blood with red and white cells.
The sensory system generally identifies danger, food source, or movement in the surroundings. The skin and eyes are important to this system.
The skeletal system gives shape to the body and protects internal organs.
The muscular system allows a fish to move and travel throughout the water. It is the largest
system within in the internal anatomy of a fish. A fish’s swim bladder allows it to stay at a particular depth in the water as it moves with its massive muscular system.
The fish’s respiratory system is very different from that of any species that has lungs. A fish
has gills that remove dissolved oxygen from the water and release carbon dioxide into the
water.
The reproductive system is associated with the process of spawning, by which new fish are
created. Spawning involves the female laying eggs that are fertilized by sperm from the male.
After a short time, the eggs hatch, and new offspring emerge.
The digestive system of a fish is very similar to the digestive systems of other animals. A fish
takes food in through the mouth, digests it in the stomach and intestines, and expels wastes
through the anus.
EXTERNAL ANATOMY
The external anatomy of a fish focuses on its curved body and its coloring, which help it
blend into its aquatic surroundings. A fast-swimming fish has a streamlined, narrow body,
while a bottom-dwelling species has a flatter shape to its top and bottom.
The skin or scales and the fins make up the major external anatomy of a fish. A fish with
skin produces a mucus that appears to be a slimy coat. It protects the fish from disease and
from invasion by harmful bacteria. The scales of some species of fish are designed to protect
from parasites and infections. Scales can flake off but will grow back over time.
The fins of fish are mostly used for stopping, turning, and other maneuvering within the
water. Some fins contain spikes or horns that serve as defensive devises. They can be used to
prick predators or to horn fishers trying to remove a fish from the hook. The fins are at various
locations on the body, including the back, belly, and sides. The rear fin is used for swimming
and accelerating through the water at high speeds.
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Lateral line
Skin
Caudal fin
Dorsal fin
Eyes
Adipose fin
Nares
Anal fin
Taste buds
Operculum
Barbels
Pelvic fin
Vertebra
Olfactory
lobe
Sensory pores
(in lateral line)
Stomach
Swim bladder
Kidney
Spinal cord
Brain
Muscle
Eye
Nostril
Mouth
Gill filament
Anus
Gonads
(ovaries or testes)
Heart
Liver
Intestine
FIGURE 1. External and internal anatomy of fish.
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Species Associated with Aquaculture
Many different species of fish are raised in the aquaculture industry. Most are raised for
production of food.
Tilapia are well suited to aquaculture production. They were originally found in the rivers
of Africa. They are used because they grow quickly and tend to reproduce easily. Tilapia are
very sensitive to colder temperatures but adapt well to closed production systems.
Bluegill are also raised in aquaculture systems because of their ability to adapt to different
environments and their ease of production. A bluegill is a sunfish identified by its deep, compressed head and small mouth.
Catfish are commonly raised in aquaculture systems. They are a widespread species found in the
United States and in high demand as a human food
source. Production of catfish is common in the
warmer climates of the South.
Trout and salmon are slightly more challenging to
raise in aquaculture systems but are desired as food
sources. They require more advanced systems with
more management and equipment.
Striped bass and walleye are also popular among
fish raised for human consumption. They are also
desired for stocking ponds and lakes for recreational
fishing.
The aquaculture industry also includes shrimp,
lobster, oyster, frog, and alligator production, among
many other types. Shrimp is the name used to
describe approximately 2,000 species of crustaceans.
They are mostly scavengers that feed slowly on both
plant and animal organisms. A prawn is a large
shrimp often raised in fresh water.
Another crustacean is the lobster, which has a hard FIGURE 2. Striped bass can be easily identified by
their markings. (Courtesy, Agricultural Research
shell and lives in saltwater regions. Lobsters are botService, USDA)
tom dwellers that feed off other lobsters, snails, crabs,
and small fish.
Oysters are mollusks. They are cultured in salt water having some current so that oxygen
and food are brought in and waste products are carried away. Water in which oysters are grown
must be free of silt and pollution.
Bullfrogs are another species associated with the aquaculture industry. They are raised for
the meat in their legs. Their legs hold great consumer demand in ethnic and domestic markets.
However, because of their more complex life cycles, frogs are not commonly raised commercially.
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Reptiles, such as alligators, are also species characterized within the aquaculture industry.
Alligators are used for their meat and hides. Alligator farms are generally located in the southern United States.
Various species of aquatic plants and algae are also grown in the aquaculture industry.
Summary:
2
The production of aquatic organisms, or aquacrops, is the industry commonly
known as aquaculture. Currently one of the fastest-growing industries in the agricultural sector, aquaculture produces a variety of species, such as fish, crustaceans,
oysters and other mollusks, bull frogs, and reptiles, along with algae and other
aquatic plants. In recent years, production has increased with the emergence of
farms devoted to tilapia, bluegill, catfish, trout, salmon, striped bass, and walleye.
Checking Your Knowledge:
´
1. What is a prawn?
2. Name a popular fish in the aquaculture industry that was originally found in
Africa and is sensitive to cold temperatures.
3. What is a fry?
Expanding Your Knowledge:
L
Explore the World Wide Web to research the vast areas of the aquaculture industry.
List freshwater fish and saltwater fish. Then, describe the key similarities and differences between the two types of fish. How does temperature, the circulatory system,
color, anatomy, and the environment affect each type?
Web Links:
:
Fish and Shrimp Production
http://www.fishfarming.com/
Alligator Farming
http://edis.ifas.ufl.edu/AC002
Bullfrog Farming
http://www.ext.vt.edu/pubs/fisheries/420-255/420-255.html
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