VERIFYING "FRESHNESS" OF TOURNAMENT FISH*
W. Steven Otwell J.C. Deng2, and
Robert W. Taylor, Jr.
Technical Paper No. 22
Department of Food Science and Human Nutrition,
Institute of Food and Agricultural Sciences and
Department of Zoology University of Florida,
Gainesville, Florida 32611
Technical Papers are duplicated in limited quantities for specialized
audiences requiring rapid access to information and may receive only limited
editing. This paper was compiled by the Florida Sea Grant College with
support from NOAA Office of Sea Grant, U.S. Department of Commerce, grant
number MA80AA-D-00038. It was published by the Marine Advisory Program
which functions as a component of the Florida Cooperative Extension Service,
John T. Woeste, Dean, in conducting Cooperative Extension work in Agri-
culture, Home Economics, and Marine Sciences, State of Florida, U.S.
Department of Agriculture, U.S. Department of Commerce, and Boards of
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of the Acts of Congress of May 8 and June 14, 1914. The Florida Sea Grant
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*Also published as part of the proceedings of the Seventh Annual Tropical
and Subtropical Fisheries Technological Conference of the Americas held
January 11-14, 1982 at New Orleans, LA.
VERIFYING "FRESHNESS" OF TOURNAMENT FISH
W. Steven Otwell1, J.C. Dengi, and Robert W. Taylor Jr.2
Department of Food Science and Human Nutrition
and Department of Zoology2
University of Florida
Gainesville, Florida 32611
Recreational fishing tournaments are increasing in popularity and
value. The exact value of this business is difficult to assess, but the
economic impacts influence specific sales, promote recreational facilities,
and attract tourism. The tournaments are usually supported by advertising,
sponsorship and entry fees (Milon et al., 1981). Tournament 'purses' often
exceed 100 to 200 thousand dollars with individual prizes in excess of
10 to 20 thousand dollars.
As a consequence of the valuable tournaments, there is a high tempta-
tion for illegal entries. The most common illegal entry is a previous
caught gamefish which has been properly frozen, then thawed for entry
during the tournament. Tournament officials and recreational fishing
organizations often request the assistance of an 'expert' judge to monitor
the weigh-ins and to declare the fish as a legal catch-of-the-day. Unfor-
tunately, most judgements are based on simple sensory assessments, i.e.,
eye clarity, gill color, flesh firmness, and odors. The assessments are
limited and can confuse the interpretation of a poorly handled 'fresh'
catch with that of a properly frozen and thawed illegal catch.
Thus a variety of simple objective techniques were investigated as
possible tests to verify the 'freshness' of gamefish caught during fishing
tournaments. The primary concern was to differentiate fresh and previously
frozen fish. Criteria for dockside techniques required simple application
with immediate results. Selection of laboratory techniques, to support
dockside results, emphasized simplicity and potential application to a
variety of fish species.
MATERIAL AND METHODS
Sensory, Torrymeter, histological and chemical techniques compared
samples from fresh catch-of-the-day and previously frozen king mackerel,
Scomberomorus cavalla. All king mackerel were caught with common recre-
ational gear trolling in waters 2 to 3 miles off Jacksonville Beach, Florida
during July and August, 1981. Whole fish were either iced or abused
immediately after catch. Iced fish were stored in ample amounts of flake
ice. Whole fish stored on deck in ambient conditions represented an
Improperly iced or abused catch. After 12 to 24 hours in ice a portion
of the iced fish was washed, tightly wrapped in plastic bags, then slowly
frozen in a walk-in freezer (-200C). Additional king mackerel for
sensory and Torrymeter assessments were sampled during an actual fishing
tournament, Greater Jacksonville Kingfish Tournament, July 29-August 1, 1981.
Visual assessments included rating for eye clarity, gill color, and
flesh firmness. The ratings were based on a 10 point visual scale with 9
samples from the supernate were used in Kjeldahl determinations of percent
nitrogen and percent protein (6.25 multiplier for conversion). Protein
extractability was expressed as grams of protein recovered per 100 grams
of muscle tissue.
RESULTS AND DISCUSSION
King mackerel caught specifically for this study had an average total
body weight of 6.6 kg (14.6 lbs.) and fork length of 91.4 cm (36 in.).
Each fish appeared in excellent health, free of noticeable, external para-
sites and fought with vigor before entering the boat. Three fish were
stored in ice and three were purposely abused by storing in ambient condi-
tions (90% relative humidity and 350C) on a shaded deck. Average internal
body temperature for all fish immediately after catch was 300C (860F).
This temperature gradually decreased to between 1 and 20C within 8 hours
ice storage, but remained between 30 and 350C in abused fish.
The visual assessments for iced and abused catch-of-the-day fish are
shown in Figure 1. Deterioration in appearance of the abused fish was
noticeable within 2 hours after catch. The most noticeable change was
decreased eye clarity which progressed to cloudy eye appearance after 8
hours. Similarly, deterioration in the flesh of the abused fish was first
noted as surface dehydration and cracking after 2 hours and softened flesh
after 4 hours. Finger pressure would leave permanent indentations in the
surface flesh after 8 hours. The gill color of abused fish decreased
from the original rich red-purple color to a dull, pink coloration after
4 hours, followed by an accumulation of slime at 8 hours. In contrast,
the appearance of the iced fish remained unchanged for 4 hours after catch.
After 8 hours in ice there was a slight decrease in eye clarity. After
24 hours of ice storage, the flesh remained relatively firm and resistant
to indentation and the gill dolor faded to a red-pink color with some
noticeable accumulation of slime. Visual distinction between iced and
abused fish was obvious, but the visual appearance of thawed fish was
similar to the abused fish. Freezing caused thick clouding of the eyes,
dehydration and cracking on the surface, softened flesh,.and faded gill
color. Thus the visual distinction between abused and previously frozen
king mackerel was not as obvious.
The Torrymeter readings from iced and abused fish were substantially
different at 2 hours after catch (Figure 1). The initial readings for
fresh caught fish (12.0) were similar to initial readings recorded for
other southeastern marine fish species (Hegen, 1981). Within 24 hours
after catch, readings from properly iced fish did not fall below 12.0,
but readings for abused fish gradually decreased to 7.0. The difference
in readings from iced and abused fish is probably due to differences in
initial spoilage, autolytic activity, and internal body temperatures.
Since recreational fishermen do not always provide proper icing, judges
can anticipate Torrymeter readings to range from 16.0 to 7.0 for catch-
of-the-day king mackerel. In contrast, readings from previously frozen
king mackerel never exceeded 4.0. The average meter reading for previously
frozen fish was 1.0. For iced, abused or frozen fish there was no appre-
ciable difference in meter readings for the three body locations.
The histological comparison between iced catch-of-the-day and previously
frozen king mackerel reveals dramatic differences in both cross and
The range (8 to 14) and mean (10.1) Torrymeter readings were within the
experimental range (7-16) noted earlier for iced and abused catch-of-the-
day fish. Sex did not influence the meter readings, but readings were
influenced by the internal body temperature. Approximately one-third
of the fish were properly iced and had an internal body temperature below
50C (410F) but higher body temperatures as a result of abuse and improper
icing depressed the meter readings (Fig. 6). A simple linear regression
of meter readings (y) as influenced by internal body temperature was
calculated to be:
y= -.llx.+ 11.6; R= -.620
During the tournament two king mackerel in excess of 13.6 kg (30 lbs.)
were encountered which had a meter reading below 4.0. These fish were
declared previously frozen and rejected from the tournament without protest
from the individual fishermen.
The Torrymeter can be used to support visual assessments to verify
catch-of-the-day fish in recreational fishing tournaments. Further support
to verify field results can include the simple histological procedure
outlined in this report. These results apply specifically to king mackerel,
but offer potential application to other recreational species.
A general interpretation of meter readings for recreational tournaments
is listed in Table 3. Fishermen should be encouraged to provide proper
icing to control internal body temperature and avoid abuse to assure higher
meter readings. In abused fish cloudy eyes, softened flesh, and low meter
readings near 4.0 could be misinterpreted as signs of a previously frozen
fish. Judges should remember that the Torrymeter can not effectively
distinguish between catch-of-the-day fish and fish caught and properly
iced beyond one day.. For multi-day tournaments rules would have to be
established to prevent carry-over from a previous days catch.
12 1 A I
., .- ABUSED
I I I I 1
12 4 8 12 2'
Hours after Catch
Average visual assessments and Torrymeter readings for catch-of-
the-day king mackerel stored in ice or abused for 24 hours. The
standard deviation for any mean visual assessments (n=3 observa-
tions per hour of measurements) did not exceed 0.5. The standard
deviation for any mean meter reading (n=9 observations per hour
of measurements) did not exceed 0.5.
FROZEN '- -- .
Cook drip loss (ml) from 40g of muscle tissue of iced and frozen
king mackerel. Catch-of-the-day represents fresh caught fish
held in ice between 12 and 24 hours.
/ .;-.-1 ''*.
y= -.11x + 11.6
* 0 2 4 2 -
I I I
10 15 20
Internal Body Temperature (0C)
Torrymeter readings per the internal body temperature for forty king mackerel caught during
a fishing tournament. Single fish are represented by o. Numerals represent duplicate
readings from different fish. For the regression equation, y= meter readings and x= internal