This document discusses lipids in fish nutrition. It defines lipids and their subclasses, and notes that they are the principal form of energy storage in animals. The document categorizes lipids and describes their composition, functions, and essential fatty acid requirements in fish. It also discusses negative aspects like the lability of polyunsaturated fatty acids to oxidation. In conclusion, lipids are an important source of energy and building blocks, but high levels can suppress growth and negatively impact product quality.

1. LIPID NUTRITION
SHALU.K
AQB 13 05 08
DEPARTMENT OF AQUATIC BIOLOGY
AND FISHERIES

2. INTRODUCTION
 Lipids are the generic names assigned to a group of fat soluble compounds
found in the tissues of plants and animals,: and are broadly classified as: a)
fats, b) phospholipids, c) sphingomyelins, d) waxes, and e) esters of glycerol
 They are principal form of energy storage
 They contain more energy per unit weight than any other biological
product(8.5 kcals metabolisable energy per gram)
 Fats are the fatty acid esters of glycerol and are the primary energy deposits
of animals.
 Fish have the unique capability of metabolizing these compounds readily and,
as a result, can exist for long periods of time under conditions of food
deprivation. (eg. Salmon )

3.  Phospholipids are the esters of fatty acids and phosphatidic acid. These are
the main constituent lipids of cellular membranes allowing the membrane
surfaces to be hydrophobic or hydrophylic depending on the orientation of the
lipid compounds into the intra or extracellular spaces.
 Sphingomyelins are the fatty acid esters of sphingosine and are present in
brain and nerve tissue compounds.
 Waxes are fatty acid esters of long-chain alcohols. These compounds can be
metabolized for energy and to impart physical and chemical characteristics
through the stored lipids of some plant and several animal compounds.
 Sterols are polycyclic, long-chain alcohols and function as components of
several hormone systems, especially in sexual maturation and sex-related
physiological functions.

4.  Fatty acids can exist as straight chain or branch chain components; many of
the fish fats contain numerous unsaturated double bonds in the fatty acid
structures
 The polyunsaturated fatty acids(PUFA) are divided inti 3 families, named afte
the shortest chain length fatty acid representing each, namely, oleic, linoleic
and linolenic acids.
 Omega (ω) system of nomenclature is used to identify the families
 Those belonging to oleic family are referred to as ω9, linoleic as ω6 and
linolenic as ω3 fattyacids
 Linoleic acid is expressed as 18:2ω6, where 18- no.of carbon atoms, 2 no. of
double bonds ω6 is the location of the first double bond relative to the
methyl( CH3) end of the molecule
 The lipid contents of most commercial aquaculture diets are less 10% mainly
due to processing problem

5. CLASSIFICATION
 Lipids may be classified into two basic groups according to presence or
absences of the alcohol glycerol

6. LIPID COMPOSITION
 FATS AND OIL
 Fuel or energy stored in animal as glycogen but also in compact form as fat
and oils
 Fat deposits in the form of triglycerides, which are esters of fatty acids and
glycerol

7.  PHOSPHOLIPIDS
 It represent the second large lipid compound after triglyceride.
 They are yellow greasy solids and soluble in lipid solvent
 The compound have a basic structural units of phosphorylated glycerol,
glycerophosphoric acid.
 The two phosphoglyerdies of primary interest in the area of nutrition are
phosphatidylcholine (PC) and phosphatidyl ethanolamine (PE)

8. Steriods
 They are very important group includes sterol, the bile acid, adrenal
hormones
 Basic structural unit of a phenanthrene nucleus linked to a cyclopentane ring
 Eg; Cholesterol important role in absorption of fatty acid

9. Other lipid
 There are several naturally occurring lipid components especially in fish
 Waxes- consist of a liphatic fattyacids esterified to alcohol other than glycerol
 Plasmologens
 Cerebrosides, sulfatides – brain and nerve tissues
 Sphingomyelins are the fatty acid esters of sphingosine and are present in
brain and nerve tissue compounds.

10. Lipid requirement of fish
 Oil and fats he traditionally used as source of energy
 The factor for evaluating a dietary lipid include
 1)digestibility
 2) the presence of any toxic material in the oil
 3)the degree of oxidation present or possible of autoxidation
 4)content of fatty acid essential for the particular species
 5)level of fat the animal can tolerate
In genera 10-20% lipid in fish diet gives optimum growth rate

11. ESSENTIAL FATTYACID REQUIREMENT OF
FISH
 One of the most widely accepted theories explaining the presence of such
high levels of 20:5w 3 and 22:6w 3 fatty acids in fish oils is related to the
effect of unsaturation on the melting point of a lipid. The greater degree of
unsaturation of fatty acids in the fish phospholipids allows for flexibility of
cell membrane at lower temperatures. The w 3 structure allows a greater
degree of unsaturation than the w 6 or w 9. This theory is consistent with the
fact that cold water fish have a greater nutritional requirement for w 3 fatty
acids, while the EFA requirement of some warm water fish can be satisfied by
a mixture of w 6 plus w 3.
 A function of essential fatty acids is to serve as a precursor to metabolic
eicosonoids(20 carbon compounds). Eicosonoids are component of bio-
membrane phospholipids , and are mobilized from the site to be metabolized
into other products.

12. Function
 Lipid in fish as a storage and provision of metabolic energy in the form of ATP
provided through beta oxidation of fatty acid
 They provide a ehicle for absorption of fat soluble nutrient such as sterol and
vitamins
 They also play as a energy source for reproduction (high level of oil content )
 Phosphoglycerides and fatty acid composition have a major role in
maintaining the structure of cellular bio membrane
 Some lipid have a special role in immune response in that some fatty acid are
precursor of leukotrienes produced by macrophages and neutrophiles and
which have immunostimulatory functions
 They are components of hormones and precursors for synthesis of various
functional metabolites such as protaglandins and eicosonoids

13.  NEGATIVE ASPECTS OF LIPIDS IN FISH NUTRITION
 The requirement by fish for PUFA of the w 3 series creates problems with
respect to feed storage. These types of fatty acids are very labile on
oxidation. The products of lipid oxidation may react with other nutrients such
as proteins, vitamins, etc., and reducing the available dietary levels or the
oxidation products may be toxic.
 The positive nutritional value of w 3 fatty acids in fish lipids for fish feeds can
become a negative factor if adequate care is not taken in the preparation and
storage of feeds. Only fresh oils with low peroxide values should be used in
feeds. Fish feed ingredients such as fish meals should be protected against
oxidation.

14. CONCLUSION
 Lipids are important source of energy, essential fattyacid and phospolipid and
provide a vehicle for absorption of fat-soluble sterol vitamins
 Also play a vital role in the structure of cell membrane, precursor for several
hormones
 Dietary lipid influences flavour and texture of feed and flesh quality of fish
 Highly digestible
 Excess lipid supresses the fatty acid synthesis , result in reduced growth
 Feeding excess lipids to produce fatty fish have and have deleterious effect
on flavour and storage life of finished product