Fish is an extremely perishable commodity due to its high water content. Spoilage of fish begins as soon as the fish dies. In high temperatures of the tropics, fish will spoil within 12-20 hours depending on species, method of capture etc.
CHARACTERISTICS OF FRESH FISH
The flesh is firm and when it is pressed, it leaves no permanent indentation.
The skin looks shiny
The eyes are clear and well rounded in shape.
The fish has a fresh smell like that of seaweeds. (Seaweeds are plants which grow in the sea).
CHARACTERISTICS OF SPOILED FISH
The flesh is soft to touch. When the flesh is pressed it leaves a permanent indentation.
The skin looks dull and has slime on the surface.
The gills look brownish in colour.
It gives a bad smell.
CAUSES OF SPOILAGE
The following are the main causes of spoilage in fresh fish:-
Bacteria Enzymatic or Autolytic spoilage Oxidation of fat B ad handling practices Insects (Blow flies)
These are very small sized organisms which live inside the intestines, on the skin and in the gills of the fish. They multiply and begin to destroy the fish as soon as it dies.
ENZYMATIC OR AUTOLYTIC SPOILAGE
Enzymes are biological catalysts and belong to a class of compounds called proteins. At death of the fish enzymes do not die but continue to function, breaking down components of fish flesh into smaller units.
This breakdown of tissues is known as autolysis, and it affects the flavour, texture and sometimes the appearance of the flesh.
OXIDATION OF FAT
In fatty fish, chemical changes involving oxygen from the air and fat of the fish may produce rancid odors and flavours. This problem is of importance when storing frozen fish for fairly long periods.
BAD HANDLING PRACTICES
When fresh fish is trampled upon or carelessly pulled out of nets, they become bruised and broken. This allows bacteria and flies to enter the fish.
The following methods can be used to reduce spoilage in fresh fish:-
- Prevention of physical damage.
- Removal of internal parts (gutting).
- Cooling of fish (icing or freezing).
- Application of salt.
PREVENTION OF PHYSICAL DAMAGE
- Remove fish carefully from nets, traps etc.
- Place fish gently in a container.
- Do not place fish on the ground.
- Keep flies, birds and animals away from fish.
- Do not step on the fish.
REMOVAL OF INTERNAL PARTS
- Cut fish open in the stomach area with clean knife.
- Remove all the intestines, liver etc.
- Remove the gills.
- Use clean water to wash the cut area and the whole fish well.
The fish should be kept cool at the right time before processing and at all stages of preparation. Cooling of fish can be done by using ice or by freezing.
APPLICATION OF SALT
There are two basic ways of using salt to preserve fish:-
- As dry salt
- As salt solution or brine
This involves the direct addition of salt to fish. Either put the salt into the gills, the gut area or use of dry salt to produce alternate layers offish and salt. It is important that the salt covers the fish both above and below. This method is usually used to prepare salted sun dried Tilapia, heterotis and other fresh water species.