Tuna Metabolism and Physiology in Captive Yellowfin Tuna (Thunnus
albacares
Abstract
At the Tuna Research and Conservation Center, in Monterey
California, captive yellowfin tuna (Thunnus albacares ) demonstrated an
increase in lipid accumulation and mortalities when fed a high calorie and
high fat diet. To determine what influence a high fat diet has on tuna
physiology, one tank (T2) holding 28 fish was designated for diet
manipulation while oxygen consumption and stomach temperatures were
used to measure changes in metabolism. No significant differences in
metabolic rate were measured between diet treatments. The low fat diet (LFD;
«1% fat content in kcal) was composed of squid and smelt while the high fat
diet (HFD; 8% fat content in kcal) only included sardines. Samples were sent
away for bomb calorimetry analysis and based on these values, an equivalent
total caloric level (28 kcal/kg/day) was maintained between diets. Individual
respirometry trials were performed in a Closed-system respirometer. Three
trials were run for each diet treatment and swimming velocity was measured
for each run to calculate standard metabolic rate (LFD: 135.70 +/- 42.79 m,
02/kg/hr; HFD: 147.54 +/- 8.89 mg 02/kg/hr; p-0.80). Whole tank metabolic
rate was measured using T2 as an Open-system respirometer with help from
the dissolved oxygen monitoring system (Program Logic Control) operated by
Monterey Bay Aquarium. Stomach temperature was measured by minilog
temperature probes and no significant difference between diets was measured
(pre-feed: p=0.91; post-feed: p-0.80).
Introduction
Yellowfin tuna (Thunnus albacares) are apex predators in an environment
sparsely populated with prey items (Olson and Boggs, 1986). They have evolved
the physiology and anatomy necessary for high rates of digestion, high rates of
growth in somatic and gonadal tissue, high rates of oxygen-debt recovery and
efficient swimming (Brill, 1996; Korsemeyer, 1996). These adaptations,
including a large gill surface area, large blood volume, large amount of red
muscle, and an elevated body temperature (Brill, 1987; Block, 1994), require
large amounts of energy to maintain. Diet is the main source of metabolic
substrates, such as fat, protein, and carbohydrates, for fuel and biosynthetic
precursors (Jobling, pg. 37-38).
Fat is a valuable metabolite for yellowfin tuna who have high energy
expenditures but unreliable prospects for energy consumption, a bioenergetic
situation often described as speculative (Olson and Boggs, 1986). It is rich in
energy, a nutritional requirement and a compact, anhydrous storage molecule
(Jobling, pgs. 10-20, Schmidt-Neilsen, pgs. 178-181, Stryer, pg. 469-472).
It is intuitive that the amount of lipids ingested should be proportionate to
the amount available for absorption, utilization, and storage. Studies on the
stomach contents of commercially netted yellowfin tuna, have shown that fish
constitute a large volume of ingested prey items (Olson and Boggs, 1986;
Maldeniva, 1996). This may overlook seasonal fluctuations in prey species
available given that tuna are general and opportunistic, rather than selective,
feeders (Olson and Boggs, 1986). The percentage of fish found in tuna
stomachs is large enough (280%) to suggest that yellowfin tuna are feeding on a
diet with adequate lipid content, as most fish species are higher in fat content
than other prey, such as cephalopods (Chuck Farwell, personal communication)
A study in sled dogs suggests that a high fat diet will increase the plasma
concentrations of free fatty acids, especially after exercise. Äfter a high level of
aerobic activity, the levels of free fatty acids in blood have been shown to
increase in actively training sled dogs (Reynolds et al., 1994) and in another
fish, the Arctic Char (Barton et al., 1995). Both studies suggest that an increase
in free fatty acid concentration in circulating blood promotes uptake and
oxidation especially in animals with high energy demands.
At the Tuna Research and Conservation Center (TRCC) in Monterey,
California, it has been a challenge to design a diet that fits the nutritional needs
of confined yellowfin tunas. Initially (September, 1994, to March, 1995), the
tunas were fed a diet of squid, sardines, and anchovies (total calories = 80
kcallkg/day) twice daily. This diet, high in both fat and calories, resulted in an
increase in lipid accumulation (in muscle tissue) and related mortalities. By
decreasing fat content and total calories fed, a decrease in intra-muscular lipid
accumulation and mortality rate was demonstrated (Perla, unpublished - 1995).
Currently, the diet consists of 82% squid and 18% smelt by wet mass and is low
in both total calories and dietary fat content (total calories = 28 kcallkglday, fat
content « 1%).
The low fat diet fed to captive yellowfin tuna at the TRCC could result in a
decrease in the availability of lipid metabolites to use and store. This change in
substrate concentration suggests a change in the metabolic cost of digestion
and storage as different substrates follow different biochemical pathways
(Schmidt-Neilsen, pgs. 145-150, 157-159). By increasing the lipid content but
maintaining a low total caloric value, the effect of a high fat diet on tuna
metabolism can be determined. Oxygen consumption and internal heat
increment are two indicators of metabolism (Schmidt-Neilsen, pgs. 178 - 179)
and can be measured using respirometry (Cech, pgs. 335 - 336) and minilog
temperature probes to gauge any effect of diet treatment.
Materials and Methods
At the TRCC, yellowfin tuna, caught off of Southern California, have been
successfully maintained in captivity. One tank, T2, (29,000 gallons) holds
twenty-eight experimental fish for Hopkins Marine Station. The water
temperature is kept at 21-22°C and the tunas are fed roughly 3 - 4% of their
body weight (Chuck Farwell, personal communication), three times a week. Body
mass was estimated from fork length measurements:
Weight = 0.0000407752 fork length?3.02
Eight smaller fish (mean mass = 3.55 kg, mean fork length = 56.51 cm),
designated as respirometry fish, were marked with yellow tags for identification.
Diet manipulation
To determine the effect of a high fat diet on tuna metabolic rate, two diet
treatments were designed. The composition of the low fat diet (LFD) was a
continuation of the regular TRCC diet - 82% squid and 18% smelt by wet mass.
The high fat diet (HFD) was composed of 100% sardines. Twenty-five
specimens each of squid, sardines, and smelt were weighed to calculate
average mass. To correct for a large variation from mean mass, squid and
sardines were separated into different size classes. Five specimens of each
group were sent to the Michelson laboratories for bomb calorimetry analyses
which measured total caloric content (kcall100 g) and percent fat, protein, and
carbohydrate. Based on these values and biomass of tank, treatments were
modified to keep total calories constant across diets (28 kcallkg/day) while
differences in fat content (LFD « 1%; HFD = 8%) could be manipulated. At 21 -
22°C, the calorie level was low enough to ensure a minimal growth rate over
experiment duration (Chuck Farwell, personal communication).
Consideration was taken in food preparation to account for size
differences of fish. Food was cut into pieces suitable for the smallest fish in T2 to
ensure that all fish were eating.
Closed-System Respirometry
A Closed System respirometer (Gooding et al, 1981, Cech, pgs. 343-345)
was used to measure routine metabolic rate of tuna under the different diet
treatments. An oxygen probe (Yellow Springs Instrument 5739 probe, attached
to a YSl 52 Dissolved Oxygen Meter) measured dissolved oxygen within the oval
tank (1,237 L). To minimize errors due to gas exchange at the waterlair
interface, all air bubbles were removed before sealing the acrylic lid to the
closed-cell foam gasket. Oxygen data was logged in spreadsheet form on a
computer.
Approximately 36 hours after a feeding, a yellow tagged fish was netted or
captured in a sling from T2, placed in the respirometer and allowed to recover
from any handling stress for about three hours. Outside stimuli were controlled
by shielding the tank with a black curtain and keeping the noise level to a
minimum. Before the high fat trials, a blue gel was placed over the light that
illuminated the tank to further decrease stress levels.
Six trials were run (n = 3 per diet treatment). Metabolic rate was
measured by stopping flow through the tank and allowing the dissolved oxygen
level to fall over time (60 minutes). Oxygen level was maintained above 80%
saturation at all times. Between runs, flow to the tank was restored for 30
minutes and the dissolved oxygen levels were allowed to return to at least 90%
saturation to avoid stressing the fish (Cech, pg. 345). Total trial duration
averaged twelve hours for each fish. The first two runs of each trial were
disregarded due to the elevated rate of oxygen consumption attributed to stress
of capture and placement in the respirometer.
A regression was calculated from dissolved oxygen level as a function of
time for each trial using the last six runs - the first two runs ignored due to
interfering stress response. The slope of the regression was used to calculate
rate of oxygen consumption:
Vo2 (mg Olkg per hour) - slope * time' volume
mass
mass = body mass of fish
time = trial duration - 60 minutes
volume = tank volume - 1,237 liters
lo correct for any increase in oxygen consumption due to increased
activity, runs were videotaped and swimming velocity was measured as time in
seconds it took a fish to swim a marked distance on the tank (average of ten
passes).
Open-System Respiromety
12 was used as an Open or Flow Through respirometer to measure
oxygen consumption of the entire population of fish in the tank (Cech, pgs. 347 -
348). A monitoring system (Program Logic Control), installed in each tank at the
TRCC by the Monterey Bay Aquarium, provided data on the levels of dissolved
oxygen in the out-flowing water of T2. The values were subtracted from in¬
flowing oxygen levels to calculate oxygen consumption. In-flowing oxygen levels
were approximated from the relationship drawn between temperature and
dissolved oxygen. Appendix 1. In-flowing water, from the Monterey Bay
Aquarium water tower, was assumed to be 100% saturated (Chuck Farwell,
personal communication) and oxygen levels were calculated accordingly,
dependent on water temperature.
Whole tank respiration was calculated using the following equation
(Gooding et al., 1981):
Vo2 (mg 021 kg per hour) = (102 inl -102 outl)* Flow
N* mass“ (1-exp(-Elow ' time)
volume
Flow = rate of exchange
volume = tank (109,765 liters)
Time = 1 hour
N = number of fish
mass = mean body mass of fish (4.9 kg)
Background metabolic rate was subtracted and a comparison of post-feeding
increase in oxygen consumption made between diets. Feeding event was plotted
as hour Ö and the areas under each curve were used to approximate total
oxygen consumed.
Stomach temperature measurements
Minilog temperature probes were used to record stomach temperature.
The probes were inserted into pieces of food, either sutured into the mantle
cavity of a squid or into a piece of sardine, to insure ingestion upon introduction
to the tank. The tuna would periodically evacuate their stomachs and the probes
could then be retrieved from the bottom of the tank and the temperature
measurements downloaded. Temperature probes recorded measurements at 3
minute intervals and remained in the fish for a mean duration of 2 days. The
maximum time between ingestion and evacuation was 6 days.
The stomach temperature measurements were converted to thermal
excess by subtracting the temperature measurements recorded from a minilog
probe suspended in the tank to record ambient water temperature. Fluctuations
in water temperature, due to the heating system, did not affect the internal
temperature of the fish immediately (Heidi Dewar, personal communication). A
lag period of 24 minutes, between changes in water and stomach temperatures,
approximated a best fit.
Calibrations
All oxygen probes were calibrated against Hach Winkler titrations which
are accurate to 0.2 mgll. Miniloggers and all other temperature probes used
were calibrated in a water bath against a thermometer previously corrected to
the Bureau of Standards thermometer.
Results
Diet Analysis
Based on data from the bomb calorimetry analysis, the total caloric
content and percent composition of different food types was shoun to vary
greatly towards a higher percentage of fat in sardines. Figure 1. The LFD was
composed mainly of squid and smelt while the HFD was composed only of
sardines. Though each diet was of equivalent caloric value (28 kcallkg/day), the
LFD was 1% fat (s1 kcal of fat/kg/day) as compared to the HFD which was 8%
fat (2.56 kcallkg/day). Figure 2.
Closed-system Respirometyy
Rate of uptake (mg O2/ kghr') was averaged from the last six runs of each
trial. Table 1. Differences in activity between fish were corrected for by graphing
oxygen consumption as a function of velocity (body lengths/second). Velocity
was measured as both centimeters per second and body lengths per second.
Oxygen consumption increased with increasing swimming speed. Figure 3. A
regression was calculated for each trial (due to erratic behavior and swimming
speeds, one trial from each treatment was discarded from the comparison (n -
2)) and extrapolated to O swimming speed (cm/s) to obtain standard metabolic
rate (LFD : 135.7 +- 30.26 mg Oø/hr.kg; HFD : 147.54 +- 6.29 mg O2/hr.kg) A
comparison across diets shows no significant differences due to treatments (p =
0.80). Table 2. The trial averages from each diet were combined and expressed
as oxygen consumption against swimming velocity which shows no difference
between the two treatment levels. Figure 4.
The results from each individual trial was also compared to previously
published results by Dewar and Graham, 1994, taken in a water tunnel where
swimming speed could be controlled. The values for these six trials were lower
than others at equivalent swimming speeds. Size may be influencing results
(mean fork length = 54.2 cm: Dewar and Graham mean fork length (largest size
class) = 51 cm). Figure 5.
Open-system Respirometyy
The LFD returns to baseline metabolic rate at approximately 34 hours
after feeding while the high fat feeding does not return to original level before 36
hours after feeding. Figure 6. The ratio of the area under each curve for HFD
and LFD whole tank respiration is 1.003. The high fat feeding shows a trend
towards a longer recovery period or longer duration of elevated oxygen
consumption.
Stomach Temperature Measurements
Though pre-feeding and post-feeding measurements within each diet
were statistically different, LFD and HFD means of the thermal excess
measurements were not significantly different. (LFD pre-feed: 0.26 +/- 004 ?C
thermal excess; LFD post-feed 0.46 +-0.03 °C; HFD pre-feed = 0.26+/- 0.025
•C. HFD O.44 +0.02 °C) (p value 0.08) Figure 7.
Discussion
By using oxygen consumption and stomach temperature as indicators of
metabolism, it was determined that no significant difference could be measured
between diet treatments. When an analysis of variance (ANÖVA) was
calculated, the variation within groups was found to be the majority of the total
variation of individual respirometry trials and thermal excess measurements.
Because of such a large variance within groups, the power of these statistical
analyses is very small (Sokal and Rohlf, pgs. 260-265). A larger sample size will
increase the sensitivity of statistical tests in determining whether the insignificant
differences are actually due to no effect from treatments or if the difference is too
small for detection without a high power test.
There was a trend in the whole tank respiration that indicated a
longer period of elevated oxygen consumption after a HFD feeding that could
indicate a higher oxygen consumption during digestion for a HFD. This trend in
post-feeding oxygen consumption (n = 1) can not be accepted as representative
without further trials. Because of the ambiguities due to variables such as small
sample size, gas exchange at the air and water interface, and outside stimuli,
the results of a high fat diet change on the metabolism of a captive yellowfin
tuna are inconclusive
Digestion of different metabolites are only few of many variables that will
influence metabolism, or the total use of energy in a system. Öther variables
that will affect the rate of energy utilization in a captive yellowfin tuna include
activity levels, oxygen availability, body size, hormones, and temperature in an
abbreviated list (Jobling, pgs. 121-145, Schmidt-Neilsen, pgs. 177-218). Even a
post-feeding increase in oxygen consumption and thermal excess is due to
multiple factors such as the energy dependent processes of metabolite
degradation, storage of excess calories, and to a small extent, mechanical work
of digestive organs (Carey et al., 1984).
Äfter an increase in dietary fat intake, there are three possible ways in
which we may expect metabolism to change; it may increase, decrease or
remain constant. The metabolic rate of the captive tuna may increase due to the
higher energy cost of fat oxidation and the availability of high energy metabolites
circulating in the blood stream, promoting the use of lipids rather than glycogen
as fuel. Since the degradation of fatty acids is dependent on low ATP levels,
high activity levels may increase the energy spent in oxidation which in turn may
increase metabolic rate (Stryer, pg. 628 - 629). Metabolism may remain constant
due the higher vield of energy from fat; it requires the oxidation of less fat than
other metabolites to gain an equivalent amount of energy (Schmidt-Neilsen, pgs.
178-180), Finally, there is a possibility that metabolism will decrease due to the
lower energy cost of converting ingested fat into free fatty acids (Jobling, pgs.
66-68) in comparison to protein or carbohydrate being first degraded into
intermediates (Acetyl Coenzyme A) and then converted to free fatty acids
(Lehninger, Nelson and Cox, pgs. 642-685).
Since the metabolic rate remained fairly constant across treatment levels,
then the lack of measurable difference could suggest that an equal amount of
total energy is being metabolized on both diets. This would increase the amount
of oxygen consumed on the high fat diet which may be offset by the fact that
more energy is being expended on the low fat diet to store excess calories as
fat. As a metabolite, fat contains twice the caloric content as protein or
carbohydrate (fat = 9.4 kcallg, protein = 4.3 kcallg, carbohydrate = 4.2 kcallg).
But, it also requires less energy to convert dietary fats than proteins or
carbohydrates into lipid stores (Schmidt-Neilsen, pg. 179). This is one
reasonable explaination for the insignificant results measured.
It is possible that the lack of any measurable differences in oxygen
consumption or stomach temperature may be due to the short length of the diet
treatment. The duration of the high fat feedings (5 weeks) may have been too
brief to elicit a physiological change in tuna metabolism. If there was a change,
the difference may have been too small for the sensitivity of the experiment and
statistical tests to quantify.
Data from free fatty acid assays of blood serum (Fletcher, 1997), sampled
from T2 at the end of each treatment, does indicate a physiological effect of the
increase in dietary fat content. As compared to samples taken from the low fat
feedings, levels of free fatty acids increased in samples taken after a 36 hour
fast after the 5 weeks of high fat feedings. This would suggest that more free
fatty acids are available both for storage and utilization and may influence the
metabolism of the captive tuna at levels of food stuff oxidation and energy
storage in lipid accumulation. Again, we must consider the multiple factors that
cause an increase in free fatty acids concentrations in blood serum, including
increased activity and starvation. (Stryer, pgs. 634 - 640)
Further Research
To elucidate the effect of a high fat diet on tuna physiology, one
suggestion for further research is a longer treatment duration and a larger
sample size. There are other questions that need to be pursued to determine the
effect of high dietary fat content on the metabolism of a captive yellowfin tuna. In
a captive tuna, what amount of fat ingested is actually absorbed? What amount
is immediately utilized and what amount is stored? And how does this compare
to the fat utilization of wild tuna? And finally, is the threshold at which excess
calories are stored as lipid or glycogen similar in captive tuna as compared to
wild tuna?
The study of fat utilization in yellowfin tuna is pertinent to their feeding
strategy. Especially in the wild, where seasonal variations in prey availability and
nutritional content compound the bioenergetic gamble that yellowfin tuna play,
there is potential for diet to influence metabolism and other physiological
processes.
Literature Cited
Adams, Marshall and James Breck. "Bioenergetics" pgs. 389 - 415 in Methods in
Fish Biology. Carl Schreck and Peter Moyle, editors. 1990. American
Fisheries Society, Bethesda, Maryland.
Barton, Kimby, Martin Gerrits, and James Ballantyne. 1995. "Effects of
Exercise on Plasma Nonesterified Fatty Acids in Arctic Char (Salvihnus
alpinus)". Journal of Experimental Zoology, v. 271: 183 - 189.
Block, Barbara and John Finnerty. 1994. "Endothermy in Fishes: a Phylogenetic
Analysis of Constraints, Predispositions, and Selection Pressures".
Environmental Biology of Fishes. v. 40: 283-302.
Carey, Frank, John Kanwisher and Don Stevens. 1984. "Bluefin Tuna Warm
Their Viscera During Digestion". Journal of Experimental Biology. v. 109:
1-20.
Cech, Joseph. "Respirometry" Pgs. 335 - 348 in Methods in Fish Biology. Car
Schreck and Peter Moyle, editors. 1990. American Fisheries Society.
Bethesday, Maryland.
Dewar, Heidi and Jeffrey Graham. 1994. "Studies of Tropical Tuna Swimming
Performance in a Large Water Tunnel". Journal of Experimental Biology.
v. 192: 13-31.
Jobling, Malcolm. Fish Bioenergetics. 1994. Chapman and Hall, London.
Korsemeyer, K., and H. Dewar, N. Lai and J. Graham. 1996. "The Aerobic
Capacity of Tunas: Adaptation for Multiple Metabolic Demands".
Comparative Biochemistry and Physiology. v. 113 (1): 17 -24.
Lehninger, Albert, David Nelson, and Michael Cox. Principles of Biochemistry
2“ edition 1993. Worth Publishers, New York.
Olson, Robert and Christofer Boggs. "Apex Predation by Yellowfin Tuna
(Thunnus albacares): Independent Estimates from Gastric Evacuation
and Stomach Contents, Bioenergetcs, and Cesium Concentrations.
Canadian Journal of Fisheries Aquatic Science. V. 43:1760 - 1775.
Perla, Bianca. 1995. "Food requirements and Lipid Accumulation in
Captive Yellowfin Tuna: Thunnus albacares .“ Hopkins Marine Station
unpublished.
Reynolds, Arleigh, Laurent Fuhrer, Harris Dunlap, Mark Finke and Francis
Kallfelz. 1984. "Lipid Metabolite Responses to Diet and Training in Sled
Dogs". Journal of Nutrition, supplement: 2754S - 27588.
Schmidt-Neilsen, Knut. Animal Physiology: Adaptation and Environment. 3“
edition. 1975. Cambridge University Press, Cambridge.
Sokal, Robert and James Rohlf. Biometry. 3“ edition. 1995. W.H.Freeman and
Company, New York.
Stryer, Lubert. Biochemistry. 3“ edition. 1988. W.H.Freeman and Company,
New York.
Acknowledgements
This project was dependent on the generous help of many
workers from Hopkins Marine Station and the Monterey Bay
Aquarium, to whom I owe much gratitude. I would especially like to
thank my advisors, Dr. Barbara Block and Chuck Farwell, for their
quidance, Ellen Freund for her advice and the use of her equipment,
Heidi Dewar for the use of her minilog probes, and Doug Fudge for his
patience and technical support.
Appendix 1 :
Relationship of Temperature to Dissolved O, Levels
Tank 2
7.5
7.4
7.3
oo 0
7.2
7.1

o 00 00
7.0
6.9
6.8
6.7
O,]=-0.117(C) + 9.62
6.6
P=0.03
6.5 -
23.0
22.0
22.5
21.5
21.0
Ambient Water Temperature ?0
ON
80
-

3888


+
Vu
3
C



a
2
.
+
+
oo
O
8.


.



-
o
a1

* *
5

IE
* *
28
53
.
55
Figure Legends
Figure 1: Caloric composition (kcal/100g) of different size classes of
squid, smelt and sardines. Results from bomb calorimetry
analysis.
Figure 2: Total calories and caloric composition of Low Fat and High
Fat Diet treatments in kcal/kg/day.
Figure 3: Results from the Closed-system respirometer for Low Fat
and High Fat Diets are plotted as oxygen consumption to activity
(or swimming velocity). Two fish, short yellow and black base,
were repeat trial subjects across the change in diet. (Each
individual fish is identified by tag description.)
Figure 4: The average oxygen consumption and swimming
velocity for each diet treatment from the Closed-system
respirometer.
Figure 6: Results from Closed-system respirometer are compared with
previously published results (Dewar and Graham, 1984)
collected in a water tunnel where swimming velocity could be
controlled. The average fork length of Diet-manipulated fish was
54.2 cm.
Figure 6: By using T2 as an Open-system respirometer for over 36
hours and subtracting out baseline (non-absorbtive, inactive
respiration, oxygen consumption demonstrates the sharp
increase after feeding (absorbtive state) that gradually returns to
baseline values for both Low Fat (LFD) and High Fat Diet (HFD).
Duration may be too short to observe full return to baseline in
HFD.
Figure 7: Stomach Temperature measurements for the Low Fat and
High Fat Diets demonstrate a significant difference between pre¬
and post-feeding (LFD p=0.003; HFD p=0.05) but no significant
differences between diet treatments (pre-feed p=0.91; post-feed
p-0.80).
30
28
26
24
22
20
18
16
14
12
10 -
8 -
6 -
Figure 1:
Bomb Calorimetry Results
Fat
Protein

Carbohydrate
E
30
29
28 -
27
26
§ 25
4 -
Figure 2 :
Distribution of Calories Across Diets
Low Fat Diet

High Fat Diet
28.00
4.94
3.96
2.57
0.59
0.24
0.21




Total
Protein
Carbohydrate
Fat
Kilocalories
350
300
250
200 -
150
100
50
0.6
Figure 3 :
Individual Respirometry Trials
- black base
long grey -
black base
1
short yellow
spot
Q
short yellow
Low Fat Diet
• High Fat Diet
0.8
1.0
Speed (body lengths second")
1.2
350
300 -
250
200
150
100
Figure 4 :
Metabolic Rate of Captive Yellowfin Tuna
Between a High and Low-fat Diet
O
Low Fat Diet
• High Fat Diet

0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8
Swimming velocity (body lengths second")
Figure 5 :
500
400
300
42cm
21 Sen
32cm
14*

5 0

228 880

800 0


.



100 125 150
50
25
Swimming velocity (cms*)
Dewar and Graham, 1994
200
150
100
50
Figure 6 :
Whole Tank Respiration
High Fat Diet
LoW Fat Diet

-50 5 10 15 20 25 30 35 40
Time (hours)
Feeding Event
Figure 7 :
Thermal Excess in Tuna:
A Comparison Across High and Low-Fat Diets
0.7
pre - feeding (p) = 0.9109 not significant
post - feeding (p) = 0.8007 not significant
0.6
0.5
2 0.4
L
0.3
0.2
0.1



0.0
Post-Feed
Pre-Feed
Pre-Feed Post-Feed
High Fat Diet
Low Fat Diet