FISH

NUTRITION
 Carbohydrates
Carbohydrates are usually defined as substances
containing carbon, hydrogen and oxygen, with the last
two elements being present in the same ratio as in
water (ie. Cx(H2O)y ).
 Classification

• The carbohydrates can be divided into two major groups according to their
chemical structure; the sugars and non-sugars.
• The simplest sugars are called monosaccharides, and these inturn can be
divided into five sub-groups depending on the number of carbon atoms
present in the molecule: Trioses (C3H6O3), Tetroses (C4H8O4), Pentoses
(C5H10O5), and Hexoses (C6H12O6)
• These monosaccharides may also inturn be linked together (with the
elimination of water) to form di, tri or polysaccharides containing two, three or
more monosaccharide units or residues respectively.
• Here the term ‘sugar’ is restricted to those carbohydrates containing less
than 10 monosaccharide units. Non-sugars are therefore carbohydrates
which contain more than 10 monosaccharide units and which do not
possess a sweet taste.
• The non-sugars can be divided into two sub-groups,
homopolysaccharides and heteropolysaccharides; the former consisting of
identical monosaccharide units and the latter of mixtures of different
monosaccharide units.
 Monosaccharides

In general all monosaccharides are soluble in water, sparingly soluble in

ethanol and insoluble in ether, are optically active, possess reducing
properties (ie. reduce Fehling's solution), can be represented by the
general formula CxH2xOx, and generally possess a sweet taste.
The chain formula of some of the more common monosaccharides can be
represented thus;
 Pentose Hexose Hexose
Triose
(C5H10O5) (C6H12O6) (C6H12O6)
(C3H6O3)

glyceraldehyde

ribose
glucose
galactose
Hexose
(C6H12O6)

mannose fructose
Carbohydrate function
Carbohydrates are synthesized in all green
plants by a process called photosynthesis,
which can be represented thus;
6CO2 + 6H2O + Light → C6H12O6 + 6O2

Within man and terrestrial farm animals dietary

carbohydrates serve as the principal source of metabolic
energy (ATP). This reaction can be represented as;
C6H12O6 + 6O2 → 6CO2 + 6H2O + 38 ATP1
In fish and shrimp no absolute dietary requirement for
carbohydrate has been established to date. This contrasts
markedly with that of dietary protein and lipid, where
specific dietary requirements have been established for
certain essential amino acids and fatty acids. To a large
extent this has been due:
• The carnivorous/omnivorous feeding habit of the majority
of farmed fish and shrimp species.
• The ability of fish and shrimp to synthesize carbohydrates
(ie. glucose) from non-carbohydrate substrates such as
protein and lipid (a process called gluconeogenesis).
• The ability of fish and shrimp to satisfy their dietary energy
requirements through protein and lipid catabolism alone if
so required.
However, despite the apparent absence of a dietary requirement for
carbohydrate in fish or shrimp, there is no doubt that carbohydrates
perform many important biological functions within the animal body.
For example; glucose, the end product of carbohydrate digestion in
animals, serves as the major energy source of brain and nervous
tissue, and as a metabolic intermediate for the synthesis of many
biologically important compounds, including the chitin exoskeleton
of crustacea, the nucleic acids RNA and DNA, and the
mucopolysaccharide mucous secretions.
Although carbohydrates may be regarded as non-essential dietary nutrients for fish
and shrimp, their inclusion in practical diets is warranted because:
• They represent an inexpensive source of valuable dietary energy for
noncarnivorous fish and shrimp species.
• Their careful use in practical diets can spare the more valuable protein for growth
instead of energy provision (a procedure called ‘protein sparing’.
• They serve as essential dietary constituents for the manufacture of water stable
diets when used as binders (ie. gelatinized starch, alginates, gums).
• Certain carbohydrate sources serve as dietary components which can increase
feed palatability and reduce the dust content of finished feeds (ie. cane or beet
molasses).
1ATP or Adenosine triphosphate contains ‘high energy’ bonds, and is the the form
in which a large part of the liberated energy is stored within the body.
Dietary carbohydrate utilization
• The ability of carnivorous fish species to hydrolyze or digest
complex carbohydrates is limited due to the weak amylotic
activity in their digestive tract.
• with carnivorous fish species (ie. salmonids) it has been shown
that high dietary carbohydrate levels depress growth, elevate
liver glycogen levels, and cause eventual mortality.
• the dietary carbohydrate being effectively utilized as a dietary
energy source or excess stored in the form of body lipid
VITAMINS
 VITAMINS

• Vitamins are a heterogeneous group of organic compounds essential for the

growth and maintenance of animal life. The majority of vitamins are not
synthesized by the animal body or at a rate sufficient to meet the animals
needs.
• They are distinct from the major food nutrients (proteins, lipids, and
carbohydrates) in that they are not chemically related to one another, are
present in very small quantities within animal and plant foodstuffs, and are
required by the animal body in trace amounts. Approximately 15 vitamins have
been isolated from biological materials;
Vitamins may be classified into two broad groups, depending on their
solubility; the water-soluble vitamins and the fat-soluble vitamins

Water-soluble vitamins Fat-soluble vitamins

Thiamine (vitamin B1) Retinol (vitamin A)
Riboflavin (vitamin B2) Cholecalciferol (vitamin D3)
Pyridoxine (vitamin B6) Tocopherol (vitamin E)
Pantothenic acid Phylloquinone (vitamin K)
Nicotinic acid (niacin)
Biotin
Folic acid
Cyanocobalamin (vitamin B12)
Inositol
Choline
Ascorbic acid (vitamin C)
 Dietary vitamin requirements
dietary vitamin requirements depend upon a number of important
factors, including:
• The feeding behaviour of the fish or shrimp species cultured.
• The vitamin synthesizing capacity of the gut microflora of the fish or shrimp
species cultured.
• The intended culture system to be used (ie. intensive, semi-intensive or extensive)
and availability of natural food organisms within the water body.
• The size and growth rate of the fish or shrimp species cultured (ie. daily vitamin
requirement per unit of body weight decreasing with increasing animal size and
decreasing growth rate).
• The nutrient content of the diet used.
• The manufacturing process to be used for the production of the ration.
• The physico-chemical characteristics of the water body and physiological
condition of the fish or shrimp species cultured.
Vitamin deficiency

Deficiency signs1
RIBOFLAVIN
Salmonids
Anorexia, poor growth, corneal vascularisation, cloudy lens,
snout erosion, spinal deformities, increased mortality rate,
severe fin erosion, fin haemorrhage, rapid opercular
movement, apparent muscular weakness, light or dark
pigmentation, striated constrictions of abdominal wall, photo-
phobia, incoordination, lethargy, anaemia (1–9)
Common carp (C. carpio)
Anorexia, poor growth, high mortality rate, haemorrhage of skin
and fins, nervousness, photo- phobia
Deficiencies due to dietary antibiotic addition
The use of feed antibiotics to treat disease outbreaks may
destroy the vitamin synthesizing capacity of the gut
microflora of fish, which in omnivorous/ herbivorous
species may play an important role toward the vitamin
requirements of the animal.