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. 2016 Jun 3:6:26990.
doi: 10.1038/srep26990.

Mammalian metabolic rates in the hottest fish on earth

Chris M Wood  1   2   3   4 , Kevin V Brix  1   2   3   5 , Gudrun De Boeck  1   6 , Harold L Bergman  1   7 , Adalto Bianchini  1   8 , Lucas F Bianchini  1   8 , John N Maina  1   9 , Ora E Johannsson  1   3 , Geraldine D Kavembe  1   10 , Michael B Papah  1   11 , Kisipan M Letura  1   12 , Rodi O Ojoo  1
Affiliations

Mammalian metabolic rates in the hottest fish on earth

Chris M Wood et al. Sci Rep. .

Abstract

The Magadi tilapia, Alcolapia grahami, a small cichlid fish of Lake Magadi, Kenya lives in one of the most challenging aquatic environments on earth, characterized by very high alkalinity, unusual water chemistry, and extreme O2, ROS, and temperature regimes. In contrast to most fishes which live at temperatures substantially lower than the 36-40 °C of mammals and birds, an isolated population (South West Hot Springs, SWHS) of Magadi tilapia thrives in fast-flowing hotsprings with daytime highs of 43 °C and night-time lows of 32 °C. Another population (Fish Springs Lagoon, FSL) lives in a lagoon with fairly stable daily temperatures (33-36 °C). The upper critical temperatures (Ctmax) of both populations are very high; moreover the SWHS tilapia exhibit the highest Ctmax (45.6 °C) ever recorded for a fish. Routine rates of O2 consumption (MO2) measured on site, together with MO2 and swimming performance at 25, 32, and 39 °C in the laboratory, showed that the SWHS tilapia exhibited the greatest metabolic performance ever recorded in a fish. These rates were in the basal range of a small mammal of comparable size, and were all far higher than in the FSL fish. The SWHS tilapia represents a bellwether organism for global warming.

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Figures

Figure 1
Figure 1. Continuous 24-h record of (A) water temperature, (B) pH, and (C) dissolved O2 (% saturation) at the SWHS site on Aug. 5, 2013.
Figure 2
Figure 2. Continuous 24-h record of (A) water temperature, (B) pH, and (C) dissolved O2 (% saturation) at the FSL site on Aug. 1, 2013.
Figure 3
Figure 3. The influence of temperature on (A) routine MO2 and (B) routine MUrea-N in the laboratory in Magadi tilapia from SWHS and FSL.
Means ± 1 SEM (N = 5–7). For (A) routine MO2 the overall effects of both population and temperature (2-way ANOVA) are significant (P < 0.05); interaction effects are not significant. For (B) routine MUrea-N, the overall effects of both population and temperature (2-way ANOVA) are significant (P < 0.05); interaction effects are not quite significant (P = 0.052). Rates for FSL fish sharing the same letters are not significantly different (P > 0.05). Rates for SWHS fish sharing the same letters are not significantly different (P > 0.05). Asterisks indicate significant differences (P < 0.05) between FSL and SWHS fish at the same temperature.
Figure 4
Figure 4. The influence of temperature on critical swimming speed (Ucrit) in Magadi tilapia from SWHS and FSL.
Means ± 1 SEM (N = 5–7). The overall effects of both population and temperature (2-way ANOVA) are significant (P < 0.05); interaction effects are not significant. Values for FSL fish sharing the same letters are not significantly different (P > 0.05). Values for SWHS fish sharing the same letters are not significantly different (P > 0.05). Asterisks indicate significant differences (P < 0.05) between FSL and SWHS fish at the same water temperature.
Figure 5
Figure 5. The influence of temperature on MO2 during swimming at increasing speeds in Magadi tilapia from (A) SWHS and (B) FSL. Means ± 1 SEM (N = 5–7).
The overall effects of population, temperature, and swimming speed (3-way ANOVA) are all significant (P < 0.05); interaction effects are not significant. Also shown (as stars) are the routine MO2 values measured in the field for freshly caught fish (SWHS, N = 15, at 41 °C; FSL, N = 10, at 33 °C).
Figure 6
Figure 6. The effect of temperature on calculated MO2(min), MO2(max), and aerobic scope in Magadi tilapia from SWHS and FSL.
Means ± 1 SEM (N = 5–7). The overall effects of population (2-way ANOVA) are significant (P < 0.05) for all three parameters, whereas those of temperature are significant only for MO2(max), but there are significant interaction effects for MO2(min) and aerobic scope. Asterisks indicate significant differences (P < 0.05) between FSL and SWHS fish at the same temperature.
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