158
ROBINA B. SUHOLES AND J. M. SHEWAN
marine white fish and herring are approximately 1 million tons, in
quality ranging from a few hours caught for fish from inshore and near
water vessels, to more than 16 days caught from the distant water
trawlers. About ly0 of the British distant water catch is condemned
annually by port health inspectors; this condemned fish is valued
presently as just over a quarter of a million pounds sterling. The spoilage or deterioration of fish, including both the loss in quality as well aa
in condemnation, is therefore of great economic importance to the
industry.
1. Fresh Jish
Although the flesh of newly caught healthy fish is usually sterile, the
integument, gills and, in ‘‘ feedy ” fish, the intestines can carry heavy
bacterial loads. The numbers range from lo2 to 105/cm2 of skin or g of
gill tissue, to 103 to 10*/ml of intestinal fluid. The variation in the
numbers is due to a variety of causes of which environmental factors
such as season and geographical area play a much greater part than say
species (Shewan, 1961, 1962b). The types of bacteria found are mainly
Gram-negative rods belonging to the genera Pseudmonas, A c h r m -
bacter, Flavobacteriurn-Cytophaga, which in newly caught fish from the
temperate zones constitute about 60-70% of the total flora. The
remainder consists of Gram-positive types belonging to the genera
Nicrococcus and Bacillus and to the loosely defined “ Coryneform ”
group. From Table IV it will be noted, however, that there are wide
variations in the percentage distribution of the aerobic bacterial
groups in fish from various parts of the world and on the present
evidence this appears to be a reflection chiefly of the differing environments in which the fish were caught. Thus, a comparison of different
species from the North Sea (cod, haddock, skate and lemon sole) showa
smaller differences than say between cod from the North Sea and
Canadian waters. In the warmer waters off Australia, India, or in the
Adriatic, the Gram-positive groups are obviously much more in evidence and this may be related to the fact that these groups are generally
more mesophilic in character than the Gram-negative ones. This ie
also borne out by the fact that only about 6% of the flora on newly
caught fish from temperate waters grow well at tempiratures much
above 25%. Moreover, direct comparison of the flora of the fish and
of the sea water in which the fish were caught reveals that the floras of
the fish aro remarkably similar to those of their surroundings (Shewan,
1961). Seasonal variations, within single species from the same area,
&1p8 almost certainly related to such factors as temperature and the
presence or absence of plankton (Liston, 1966 ; de Silva, 1960).
ROBINA B. SUHOLES AND J. M. SHEWAN
marine white fish and herring are approximately 1 million tons, in
quality ranging from a few hours caught for fish from inshore and near
water vessels, to more than 16 days caught from the distant water
trawlers. About ly0 of the British distant water catch is condemned
annually by port health inspectors; this condemned fish is valued
presently as just over a quarter of a million pounds sterling. The spoilage or deterioration of fish, including both the loss in quality as well aa
in condemnation, is therefore of great economic importance to the
industry.
1. Fresh Jish
Although the flesh of newly caught healthy fish is usually sterile, the
integument, gills and, in ‘‘ feedy ” fish, the intestines can carry heavy
bacterial loads. The numbers range from lo2 to 105/cm2 of skin or g of
gill tissue, to 103 to 10*/ml of intestinal fluid. The variation in the
numbers is due to a variety of causes of which environmental factors
such as season and geographical area play a much greater part than say
species (Shewan, 1961, 1962b). The types of bacteria found are mainly
Gram-negative rods belonging to the genera Pseudmonas, A c h r m -
bacter, Flavobacteriurn-Cytophaga, which in newly caught fish from the
temperate zones constitute about 60-70% of the total flora. The
remainder consists of Gram-positive types belonging to the genera
Nicrococcus and Bacillus and to the loosely defined “ Coryneform ”
group. From Table IV it will be noted, however, that there are wide
variations in the percentage distribution of the aerobic bacterial
groups in fish from various parts of the world and on the present
evidence this appears to be a reflection chiefly of the differing environments in which the fish were caught. Thus, a comparison of different
species from the North Sea (cod, haddock, skate and lemon sole) showa
smaller differences than say between cod from the North Sea and
Canadian waters. In the warmer waters off Australia, India, or in the
Adriatic, the Gram-positive groups are obviously much more in evidence and this may be related to the fact that these groups are generally
more mesophilic in character than the Gram-negative ones. This ie
also borne out by the fact that only about 6% of the flora on newly
caught fish from temperate waters grow well at tempiratures much
above 25%. Moreover, direct comparison of the flora of the fish and
of the sea water in which the fish were caught reveals that the floras of
the fish aro remarkably similar to those of their surroundings (Shewan,
1961). Seasonal variations, within single species from the same area,
&1p8 almost certainly related to such factors as temperature and the
presence or absence of plankton (Liston, 1966 ; de Silva, 1960).