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Figures
- Fig. 5.
Diving behavior of Atlantic bluefin tunas recorded with electronic tags. Data on ambient and internal temperature and pressure are recorded at 2 min intervals for two Atlantic bluefin tuna in the North Atlantic. (A) Fish 521; 219 cm, 179 kg; (B) Fish 485; 208 cm, 154 kg at time of release. Days shown are representative of behaviors observed daily in the Gulf of Maine (A) and Flemish Cap (B). Both fish show a pattern of rapid diving into cool water and regular returns to the surface. Conservation of internal body temperature is also shown. The lack of any temperature effect (significant cooling) on the peritoneal cavity suggests that the continuous resurfacing may be associated with physiological requirements for rewarming of the heart and reoxygenation of the tissues.
- Fig. 1.
Heart rate from a Pacific bluefin tuna heart perfused with Ringer's solution in situ. Cardiac output pressure data from a single fish at 30°C (top), 15°C (middle) and 2°C (bottom) are shown.
- Table 1.
Temperature effects on cardiac parameters
Conditions Parameter Temperature (°C) Standard Maximal N Heart rate (beats min-1) 2 16.1±0.6a 13.3±0.9a 3 5 23.1±1.4a 21.1±1.4a 6 10 36.4±2.4b 33.4±3.4b 6 15 54.7±2.2c 55.3±3.5c 8 20 78.2±3.1d 83.8±5.2d 7 25 100.1±2.7e 104.5±6.5e 6 Stroke volume (ml kg-1) 2 0.86±0.01a 1.32±0.10 3 5 0.86±0.07a 1.24±0.07 5 10 0.57±0.05b 1.21±0.03 4 15 0.37±0.02c 1.23±0.04 6 20 0.23±0.02d 1.11±0.03 3 25 0.18±0.02d 1.06±0.07 4 Cardiac output (ml kg-1 min-1) 2 14.2±0.9 18.1±1.7a 3 5 19.4±2.0 26.7±3.0a 5 10 20.6±2.6 40.8±5.0b 4 15 20.5±1.3 67.5±3.8c 6 20 17.0±2.3 89.8±7.5d 3 25 18.1±2.1 106.2±5.1e 4 Power (mW g-1) 2 0.46±0.03 0.43±0.05a 3 5 0.61±0.08 0.74±0.11a 5 10 0.67±0.11 1.41±0.19a 4 15 0.65±0.06 2.75±0.30b 6 20 0.50±0.07 3.59±0.76b,c 3 25 0.65±0.09 4.38±0.68c 4 -
Values are means ± s.e.m.
Values within a column that do not share a letter are significantly different (P<0.05); where no letters appear, no significant differences were detected.
Standard conditions: input pressure 0-0.05 kPa, output pressure ∼6 kPa; maximal conditions: input pressure ∼2.4 kPa, output pressure >10 kPa. See text for details.
-
- Fig. 2.
Cardiac performance in bluefin tuna in situ. Values of cardiac parameters were recorded in spontaneously beating bluefin tuna hearts perfused in situ with oxygenated Ringer's solution at temperatures of 2–25°C. At each test temperature, values were recorded at standard conditions (open circles) of ambient input pressure and then input pressure was elevated to maximize stroke volume and cardiac output (A–C, filled circles). Input and output pressures were then elevated until power output was maximized (D, filled circles). (A) Heart rate, (B) stroke volume, (C) cardiac output, (D) power. Values are means ± s.e.m.; N=3 (2°), N=4 (10°, 20°, 25°), N=5 (5°), N=6 (15°). Significant differences between standard and maximal conditions (P<0.05) occur in A at 2°C only, in B at all temperatures, in C at all temperatures ≥5°C and in D at all temperatures ≥10°C. Significant differences between temperatures are indicated in Table 1. For details of standard and maximal conditions, see Materials and methods.
- Fig. 3.
Comparison of cardiac performance in situ in three tuna species. Maximal values of cardiac parameters recorded in spontaneously beating hearts of albacore tuna (red triangles), bluefin tuna (blue squares) and yellowfin tuna (yellow diamonds) are presented. (A) Heart rate, (B) stroke volume, (C) cardiac output, (D) power output. Sample sizes for bluefin tuna are as in Fig. 3. Values are means ± s.e.m.; for yellowfin tuna, N=4 (10°, 25°), N=5 (15°, 20°); for albacore tuna, N=1.
- Fig. 4.
Scope for increase in cardiac output (open symbols) and myocardial power output (filled symbols) of in situ perfused bluefin tuna hearts at temperatures of 2–25°C. Scope was calculated from data in Table 1 as the percentage difference between mean values of cardiac power output at standard conditions vs. maximal flow (cardiac output) or maximal power (power output) conditions.
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