Richard D. Miles and Jacqueline P. Jacob
2
High
quality fishmeal is recognized by animal nutritionists as an excellent
source of protein, energy, minerals and vitamins. Worldwide, millions
of tons of fishmeal are produced annually. The majority of the fishmeal
produced is included in commercial diets for poultry, swine, dairy
cattle, mink and fish.
Good quality fishmeal demands a higher
price than other high protein feedstuffs. Its proper use, however,
requires a knowledge of not only its nutrient profile but of how it was
produced. An understanding of fishmeal production will give users a
better understanding of how the various factors interact to influence
the quality of fishmeal.
What Types of Fish are Used?
Fishmeal can be made from almost any type of fish but is generally
manufactured from two main types. These two types of fish differ both
in their ability to store oil as well as where in the body oil is
stored.
The first type includes a group referred to as "lean
fish." This includes such species as cod and haddock. In these species
the oil is stored primarily in the liver. The flesh (fillets) contain
very little oil. Fishmeal from this type of fish has a low oil content
(2 to 6%) since the livers are removed beforeprocessing. Of course, if
the livers are added back, or the whole fish is used, the oil content
would be higher. The whole fish is not usually used since cod and
haddock are prized for the fillets. Since the fillets are used for
human consumption, the fishmeal from these lean fish are made
principally from the offal (white fish frames) remaining after
filleting. "White" fishmeal commonly contains a higher concentration of
ash (minerals) since the bony frames (head and racks) of previously
filleted cod, haddocks, etc. are used. White fishmeal constitutes only
10% of the world fishmeal production.
The second type of fish
used to manufacture fishmeal stores oil in certain parts of the flesh.
They are high oil fish and, unlike the lean fish, are not prized for
their fillets. They are commonly referred to as "industrial fish."
Such species as herring, menhaden, anchovy, pilchard, sardines and
mackerel fall into this category. Approximately 90% of the world
fishmeal production is from these high oil species.
Most species
of fish used for the production of fishmeal have a similar protein
content that averages approximately 16% in the whole fish. This whole
body protein content will vary by only plus or minus 2 to 3%. The
fishmeal derived from these fish will, therefore, all be fairly similar
in protein content. Theoil (fat) content in fish species is much more
variable than their protein content. The amount of oil in fishmeal is
directly dependent on the efficiency of the oil removal at the time of
processing.
Where are the Fish Processed?
Fish can be processed at sea in factory ships or caught and stored
until they are transported to a coastal processing factory. Fish is a
highly perishable raw material and spoilage will occur if not processed
in a timely manner. Preservation using chemicals, ice or refrigerated
sea water is common.
How are the Fish Processed?
Fishmeal is made by cooking, pressing, drying and grinding the fish.
When no oil needs to be removed, such as with lean fish, the pressing
stage is often omitted. During cooking, the fish move through a long,
steam-jacketed, screw conveyor cylinder. Cooking coagulates the
proteins and is a critical process responsible for sterilizing the
product and preparing it for liquor (a mixture of oil, water and
protein) removal. Once cooked, the liquor is removed by pressing. The
solid residue that remains after pressing is called "presscake." The
liquor is centrifuged to remove the oil. This oil is often further
refined before being transported to storage tanks. Prior to storage, it
is essential to add an antioxidant. The antioxidant will stabilize the
oil so that oxygen will not cause damage during storage. The stored
oil must not come into contact with air, heat or light in order for its
quality to be maintained until it can be incorporated into feeds for
poultry, pets, fish or other uses.
The liquid removed from
presscake is referred to in the processing industry as "stickwater."
This liquid may contain as much as 20% soluble protein and is
valuable. The stickwater is evaporated to a thick syrup containing 30
to 50% solids. This material can be sold as "condensed fish solubles"
or it can be added back to the presscake and dried with it. Therefore,
one can purchase presscake meal or a whole meal (where all of the
solubles have been added back).
The meals are then dried so that
the moisture content is low enough to allow the meal to be stored and
transported without mold or bacterial growth. If overdrying occurs, the
meal can be scorched and the nutritional value of the meal will be
adversely affected. Drying can be either direct or indirect. Direct
drying is the most rapid and requires very hot air to be passed over the
meal as it is rapidly tumbled in a cylindrical drum. If this process
is not carefully controlled the fishmeal may be scorched. Indirect
drying requires a steam-jacketed cylinder or a cylinder containing
steam-heated discs which tumble the meal.
Once the fishmeal is
dried it has to be ground, screened to the correct particle size, packed
in bags or stored in silos for bulk delivery to companies throughout
the world.
What Type of Fishmeal is Commonly Produced in the U.S.A.?
In the U.S.A., the majority of the fishing industry is in the Gulf of
Mexico and the Atlantic Ocean. The main industrial fish harvested is
menhaden. In fact, 98% of the fish oil produced in the U.S.A. is from
menhaden, a high oil species. The oil is considered by fish processors
to be a by-product of fishmeal production. This is just the opposite
viewpoint taken by soybean processors. These processors consider the
soybean meal to be a by-product of oil production. No matter which
viewpoint is taken, however, both "by-products" have an important place
in animal diets.
Smaller quantities of fishmeal produced in the
U.S.A. are made from herring, redfish, and white fish. This fishmeal is
low in oil, and comparatively higher in ash than the fishmeal from
menhaden because of the relatively large amount of bone it contains
compared to the amount of muscle.
How Can You Identify Good Quality Fishmeal?
Good quality fishmeal is a brown powder which will average between
60% and 70% protein. The oil content in the meal will range from 2% to
greater than 14%. The moisture level will commonly range from 6 to 12%.
The ash content will range from 18% (more common for an industrial
fishmeal) to 25% (more common for a white fish meal).
The odor of
fishmeal, as would be expected, is that of fish. It is easily
distinguished from other ingredients. If an acrid "scorched" smell is
present this usually indicates overheating or scorching. If this
occurs, a blackish dark-brown color is common and the quality of protein
is usually affected in a negative manner.
EUROPEAN UNION
Scientists have found the fossils of an extinct species of porpoise with
a very long chin. This species of porpoise may have used its long lower
jaw to probe the sea floor for food. 
Scientists have developed a new aquatic robot that completely replicates
realistic movements of fish producing an illusion of a real animal. The
robot is also identical in basic engineering. (Photo :
buymelunch/Flickr)