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Biological Aspects & Chemical
Composition of Fish
Quality and Safety Issues in Fish Handling
----A course in quality and safety management in
fishery harbours in Sri Lanka
- building for better NARA, DFAR, ICEIDA and UNU-FTP
Department of Fisheries and
Aquatic Resources (DFAR)
National Aquatic Resources Research
and Development Agency (NARA)
United Nations University Fisheries
Training Programme (UNU-FTP)
Icelandic International
Development Agency (ICEIDA)
Sri Lanka
Sri Lanka
Iceland
Iceland
1
Content
• Biological aspects
• Anatomy and physiology
• Chemical composition
2
Learning objectives
After this lecture participants will be familiar with:
• biological aspects, anatomy and physiology
• chemical composition and factor affecting
composition of fish.
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BIOLOGICAL ASPECTS
Classification
Aquatic vertebrates
Use gills to obtain oxygen
Have fins
Vertebrate classes
Sharks and rays
Bony fish
– Generally important and widely distributed
Scientific
grouping
Biological
characteristics
Cyclostomes
jawless fish
Chondrichthyes
cartilaginous fish
high urea content in muscle
sharks, skate, rays
Teleostei or bony
fish
pelagic fish
fatty fish (store lipids in body
tissue)
herring, mackerel, sardine tuna,
sprat
demersal fish
lean (white) fish (store lipids in
liver only)
grouper, skates, ray fish
Technological characteristics
Examples
lampreys, slime-eels
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Anatomy
5
Biological aspects of fish
related to quality
•
•
•
•
•
Shape of fish
The skeleton
Muscle anatomy and function
Skin
Cardiovascular system
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The shape of fish
• There are basically two shapes of fish: round fish and flat fish.
• The physical shape of a fish can also be a problem for spoilage since
spoilage bacteria grow extensively on the surface of fish.
• Generally, fish that have a high surface to weight ratio, the rate of
deterioration may also increase.
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The skeleton of fish
• Fish have a vertebral column and a cranium covering the brain.
• In the trunk region they have lateral processes that bear ribs.
• There is also a corresponding number of false ribs or pin bones.
• Pin bones cause a great deal of trouble when fish are being filleted or
processed.
(Huss, 1995)
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Muscle anatomy
• Most fish muscle tissue
is white
• Many fish have a certain
amount of dark tissue
• The proportion of dark
to light muscle varies
with the activity of the
fish.
(Huss, 1995)
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Dark and white muscles
• There are many differences in the chemical composition of
the white muscle and dark muscle
• White muscle has more protein than dark muscle
• Dark muscle contains more lipid, myoglobin, histidine…
• Ideally suited for oxidative metabolism
• Rancidity can be a problem in dark muscle
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Skin
• Skin covers the outer surface of the body and
protects the muscle.
• Skin secretes a mucus which makes the fish
slippery
• The mucus has main functions:
• Help the passage of the fish through the water
by reducing friction.
• Give protection against attacks of bacteria and
others microscopic organisms which would
otherwise infect the fish.
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Cardiovascular system
1.
2.
3.
4.
5.
6.
The heart pumps blood toward the gills.
The blood is aerated in the gills.
Arterial blood is dispersed into the capillaries where the transfer of oxygen
and nutrients to the surrounding tissue takes place.
The nutrients from ingested food are absorbed from the intestines, then
transported to the liver and later dispersed in the blood.
In the kidneys the blood is purified and waste products are excreted via the
urine.
Bleeding is an important step to prevent the formation of histamine in fish
(Huss, 1995)
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Chemical composition of tuna
•
•
Water
Protein
:
:
70.4 – 71.0 %
~ 23 %
Highly digestible protein, essential amino acids
•
Lipids
:
1 – 4.6 %
Essential & Omega –3 fatty acids
•
•
•
•
•
•
Vitamins A,D, E
Minerals Na, K, Ca, P
Carbohydrates
Non-protein nitrogenous compounds.
Enzymes
Other
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Lipids
The lipid content varies considerably in fish, 0,1-30%.
Classify fish according to fat content.
Lean fish (< 1% fat) e.g cod, haddock.
semi-fatty fish (<10%) halibut, barracuda, shark, and tuna.
fatty fish (>10%) salmon, herring and mackerel.
Essential fatty acids
Human body can't produce.
Must be consumed through the diet.
Linoleic and linolenic acids.
Important for cellular health, proper glandular functioning, oxygen
transport, circulation, cholesterol protection plus healthy skin, mucous
membranes and nerves.
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Omega 3 fatty acids
Decrease
=>
Increase
=>
Prevent
Very low density lipoprotiens (VLDL)
Low density lipoprotiens (LDL)
Cholesterol (CL)
Excess production of eicosanoids
High density lipoprotiens (HDL)
=>
Main Compounds =>
Coronary heart disease
Arthritis
Blood pressure
Thrombosis
Tumor growth
EPA, DHA
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Factors affecting composition of fish
Season
Spawning (fat content & water)
Age
Young, sexually mature fish
Sex
Female & male
Environment
Feed, water temperature
Body Location
Light & dark muscles
Type of fish
Sharks and ray fish contain high urea
Pelagic & demersal fish
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Seasonal variation in the chemical composition
of (a) herring fillets (Clupea harengus) and (b)
mackerel fillets (Scomber scombrus)
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References
• Huss, H.H. Quality and quality changes in fresh fish.
FAO 348, 1995
• Donald R.Swift MSC. Aquaculture training manual,
1985
• Ian Dore. Shellfish ,1991.
• R.Kreuzer. Cephalopods: Handling, processing and
products. FAO 254, 1984.
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