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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

Icelandic International Development Agency (ICEIDA)

Iceland

United Nations University Fisheries Training Programme (UNU-FTP)

Iceland

National Aquatic Resources Research and Development Agency (NARA)

Sri Lanka

Department of Fisheries and Aquatic Resources (DFAR)

Sri Lanka

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Content

• Biological aspects • Anatomy and physiology • Chemical composition

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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 oxygenHave fins

Vertebrate classes Sharks and raysBony fish

– Generally important and widely distributed

Scientific grouping

Biological characteristics

Technological characteristics Examples

Cyclostomes jawless fish   lampreys, slime-eels

Chondrichthyes cartilaginous fish high urea content in muscle sharks, skate, rays

Teleostei or bony fish

pelagic fishfatty 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

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Anatomy

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• Shape of fish

• The skeleton

• Muscle anatomy and function

• Skin

• Cardiovascular system

Biological aspects of fishrelated to quality

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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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• 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.

The skeleton of fish

(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. The heart pumps blood toward the gills.2. The blood is aerated in the gills.3. Arterial blood is dispersed into the capillaries where the transfer of oxygen

and nutrients to the surrounding tissue takes place.4. The nutrients from ingested food are absorbed from the intestines, then

transported to the liver and later dispersed in the blood.5. In the kidneys the blood is purified and waste products are excreted via the

urine.6. Bleeding is an important step to prevent the formation of histamine in fish

(Huss, 1995)

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• Water : 70.4 – 71.0 % • Protein : ~ 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

Chemical composition of tuna

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LipidsThe 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

Very low density lipoprotiens (VLDL)Decrease => Low density lipoprotiens (LDL)

Cholesterol (CL)Excess production of eicosanoids

Increase => High density lipoprotiens (HDL)

Prevent => Coronary heart diseaseArthritisBlood pressureThrombosisTumor growth

Main Compounds => 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.