III.1. Prevention of spoilage of fish before processing
A great deal of spoilage may occur before the fish is processed.
The bacterial and chemical changes which cause spoilage proceed rapidly at the
temperature at which tropical fish normally live (in the range of 25-30°C).
In general, the lower the temperature of the fish, the slower the change which
causes spoilage. Furthermore, spoilage may be reduced if fish are handled
properly, and good hygienic measures are adopted. A few measures for avoiding or
minimising spoilage are briefly described below.
(i) Improvement of landing facilities and distribution.
Very often, whenever unexpectedly large catches are taken, landing facilities
and the distribution system cannot handle the surplus of fish. Thus, a long
period of time may elapse before the fish can be processed. Consequently, a high
percentage of the fish may become unsuitable for processing. It is therefore
important to expand cold storage facilities in proximity of the catch areas
whenever sufficient and/or adequate transport facilities (e.g. trucks equipped
with a refrigeration system) are not available. Alternatively, processing plants
may be located near the catch areas in order to avoid the need for extensive
(ii) Maintaining the fish at low temperatures. To
minimise spoilage, fish should be kept as cool as possible immediately after
catching until processing starts. If tropical fish are chilled with ice, they
may be kept in an edible condition for an increased period. The actual length of
time depends very much on the type of fish, but may be as long as three weeks.
However, in many areas far away from major towns, ice may not be available in
sufficient quantities. Fish may then be kept relatively cool by other means,
including the following:
- keeping the fish in the shade out of direct sun,
- placing damp sacking over the fish. This helps reduce the
temperature as the water evaporates. The sacking must be kept wet and the fish
must be well ventilated.
- mixing the fish with wet grass or water weeds in an open-sided
box so that the water can evaporate and cool the fish. In this method, the fish
should be kept continuously wet.
(iii) Maintaining a hygienic environment. Fish which have
been handled cleanly and carefully will be in a better condition than fish which
have been handled carelessly; they can, therefore, be worth more money.
Before processing starts, attention to the following points is
- To keep the fish as clean as possible. Washing
with clean water will remove any of the bacteria present on the fish skin,
especially in the presence of mud.
- To keep the fish cool, chilled in ice or chilled water, if
possible, at all stages before processing starts. Fish spoilage is a continuing
process: once a particular stage of spoilage has been reached no amount of good
practice or processing can reverse it.
- To avoid damaging fish by careless handling. If the skin is
broken this will allow bacteria to enter the flesh more quickly and spoilage
will be more rapid. This sort of damage can be caused by walking on fish and by
the use of a shovel. If the guts can be removed and the gut cavity washed
carefully, this will reduce the number of spoilage bacteria present; however, in
some areas, the purchaser requires whole fish so that this practice may lower
the value of the