NUTRITION IN AQUACULTURE
AND RANJIT BORDOLOI4
of Fisheries, Assam Agricultural University, Raha, Nagaon — 782103,
NAIP Cell, Assam Agricultural University, Jorhat — 13, Assam.
aquaculture industry as such has grown at a significant rate over the
last few decades. During this period it has begun to be transformed
from an art to a science, however even to this date this transition
remains far from complete. As in other forms of animal husbandry,
feeds and feeding are crucial elements in the culture of aquatic
animals. Feed cost is considered to be the highest recurrent cost in
aquaculture, often ranging from 30% to 60%, depending on the
intensity of the operation. Any reduction in feed costs either
through diet development, improved husbandry or other direct or
indirect means is therefore crucial to the development and well being
of the industry. Importance has been given to simple feed
formulations, utilization of non — conventional feedstuffs and feed
processing. In this regard the aspects related to feeds and feeding
which are increasingly becoming important to the aquaculture
industry, in particular feeds and feeding in relation to the
environment and the aquafeed industry.
many years water quality has been the most important limitation to
fish production. Advances in life support technology have been
substantial in recent years, and nutrition is increasingly regarded a
key limitation to increased production efficiency as well as the
growth and propagation of "new" species. Feeding of artificial
diet balanced in all nutrients has assumed foremost importance in
aquaculture industry. Artificial feeding is an essential practice in
an aquaculture operation accounting for over 60% in total input cost.
composition of fish diets
fish diets tend to be very high in protein. Foods for fry and
fingerlings frequently exceed 50% crude protein. As growth rate
decreases and fish age, protein levels in diets are decreased
accordingly. Protein levels on grow-out diets often approach or
exceed 40% crude protein, while maintenance diets may contain as
little as 25-35%. In addition to decreasing the protein content of
the food as fish grow, the particle size must also be changed. Many
fish require live food when they are hatched because their mouth
parts are so small. Some fish are large enough to place on a fry diet
immediately without having to bother with the expense and labour
needed for live foods.
meal should be a major protein source in fish diets. There are
essential amino and fatty acids that are present in fish meal but not
present in tissue from terrestrial plants or animals. Low cost
formulations in which fish meal has been eliminated and replaced by
less expensive proteins from terrestrial sources (ie soybeans) are
not recommended for fish. Fish meal and fishery by-products have high
lipid content and therefore rancidity can be a problem if foods are
not properly stored. Feed storage is discussed briefly below.
In addition to the
concern for essential amino acids that may be present in fish meal,
fish require long chain fatty acids (C20 and C22) that are not found
in tissue from terrestrial organisms. Fish meal, shrimp meal and
various types of fishery by-products are the source for these
essential fatty acids. In addition, crustacean by-products serve as a
source of carotenoid pigments that are excellent for colour
enhancement. There is a high oil content associated with carotenoid
pigments, so vitamin E supplementation is recommended when these are
Most fish require
dietary ascorbic acid (vitamin C). This becomes very important if
fish are reared in a poorly lit area where algae cannot grow, or if
they are so crowded that they cannot consume any natural food items
that might be in the water. Ascorbic acid added to fish foods should
be phoshorylated to stabilize the vitamin and increase storage time.
In addition, vitamins A, D, E and B complex should be added to fish
foods. The concentration of vitamin E is often inadequate, especially
in diets that are high in fat. If fish are housed in natural systems
with algae and phytoplankton, and stocking rates are not too great,
then vitamin supplementation seems to be less important, presumably
because of the availability of natural food items.
fish feeds usually contain relatively high amounts of fish meal
and/or fish oil, they are very susceptible to rancidity. In addition,
ascorbic acid is highly volatile, but critical to normal growth and
development of most species of fish. For these reasons, fish feeds
should be purchased frequently, ideally at least once a month and
more frequently if possible. Feeds should be stored in a cool, dry
place and should never be kept on hand for more than three months.
Refrigeration of dry feeds is not recommended because of the high
moisture content of that environment. Freezing is an acceptable way
of extending the shelf life.
milled fish foods are usually sold as dry or semi-moist pellets or as
flakes. Pellets are typically the most complete diets. They are
cooked, and, if marketed as a complete ration, the nutrition in each
particle should be uniform. Disadvantages include the potential for
rapid sinking unless the pellet is extruded. In addition, the pellet
size is very important. It may be impossible to manufacture a
particle small enough for some fish, especially juveniles of many
species. For larger animals, a very small pellet may be unacceptable.
Semi-moist diets are soft and compact. Many of these are expensive,
but they tend to be high quality diets and may be an excellent choice
for some species.
have been used extensively in the ornamental fish industry for many
years and have the advantage of being soft enough for very small fish
to consume. They also sink very slowly. Unfortunately, the volume
required to meet the nutritional needs of the animals may be
associated with rearing of live foods is improving rapidly. This is
having a positive impact on larval rearing, a frequent bottleneck for
commercialization of "new" species. Rotifers are the smallest
live food that is routinely used for larval rearing. Newly hatched
brine shrimp are larger, but still quite small, and are commonly used
in fish hatcheries. Cultured live foods can provide a source of high
quality nutrition, but care must be taken to avoid perpetuation of
infectious disease. Use of wild caught food items is also risky
because of the potential for disease introduction.
disease is often a diagnosis of exclusion. Other explanations for the
problem are ruled out and then the feeding program is critically
evaluated. Several examples of nutritional disease merit mention.
These include starvation, scoliosis and nutritional anemiaa. Each is
discussed briefly below.
usually the result of poor husbandry and, in many cases, is a sequel
to environmental problems. A poorly designed or maintained system is
likely to develop water quality problems with related morbidity or
mortality among the fish. In an effort to correct the water quality
problems aquarists may cut back on feed to the point where the
animals are in a negative caloric balance and begin to lose weight.
If the problem becomes chronic, starvation can result.
The classical cause
of scoliosis, or "broken back disease" in fish is ascorbic acid
deficiency. Improvements in feed manufacture, including
phosphorylation of vitamin C, and feed storage, have decreased the
incidence of nutritionally derived scoliosis. Still, ascorbic acid
deficiency must be considered as a possible cause of scoliosis and a
thorough review of feeding practices is warranted when evaluating
is caused by folic acid deficiency. The diagnosis is often based
initially on history, with multiple units developing similar signs at
the same time. When suspected, a sample of feed should be frozen for
later analysis, but all affected ponds should have the feed changed
immediately to a fresh lot. The problem is caused by bacterial
contamination of feed, so it is not related to particular brands or
preparation must be done on logical approach for simple formulations
that should be location specific and resource oriented using a large
proportion of alternative protein sources with due consideration for
less expensive feeds to support sustainable and economically sound
aquaculture. Establishment of regional feed centres should be given
due priority to understand and identify farmers' feed related
problems for their development that may go a long way to village
level production of improved farm made feeds through small feed
mills, particularly by small farmers who account for more than 80% in
Silva, S.S. and Anderson, T.A. 1998. In: Fish Nutrition in
Aquaculture, London, UK, 287 pp.
T. 1988. Nutrition
and Feeding of Fish.
Van Nostrand Reinhold, New York, NY 260 pp.
R.J. 1989. Nutritional pathology of teleosts, In: Fish
R.J. Roberts (Ed), Balliere-Tindall, London Pp. 337-362.
R.A. 1992. Nutrition and feeding of tropical fish, IN:
Aquariology: The Science of
J.B. Gratzek (ED).Tetra Press, Morris Plains, NJ Pp. 197-206.
Seafood — Fish — Crustacea
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