Mammalian metabolic rates in the hottest fish on earth

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.

Niche divergence facilitated by fine‐scale ecological partitioning in a recent cichlid fish adaptive radiation

“…Based on studies of A. grahami , Alcolapia exhibit the highest recorded metabolic rate of teleosts (e.g., Wood et al. , ), around half of which is thought to be due to the requirements for acid‐base regulation in high pH (Wood et al ). To support this increased metabolic rate, the fishes exhibit continuous feeding (Trewavas ; Johansson 2014).…”

“…The high pH and temperature of Natron/Magadi promotes high levels of cyanobacterial and algal production (Grant 2006); but places a large osmotic pressure on Alcolapia, with substantial physiological demands. Based on studies of A. grahami, Alcolapia exhibit the highest recorded metabolic rate of teleosts (e.g., Wood et al 2002Wood et al , 2016, around half of which is thought to be due to the requirements for acid-base regulation in high pH (Wood et al 2002). To support this increased metabolic rate, the fishes exhibit continuous feeding (Trewavas 1983;Johansson 2014).…”

Developmental changes in oxygen consumption and hypoxia tolerance in the heat and hypoxia‐adapted tabasco line of the Nile tilapia Oreochromis niloticus, with a survey of the metabolic literature for the genus Oreochromis

“…Because 35°C is a temperature at which few teleosts thrive, very few comparable data are available. Noteworthy is the Lake Magadi tilapia Alcolapia grahami (Boulenger 1912) , capable of living in extraordinarily warm waters of up to 43 °C (Wood et al, ). Extrapolating data presented in this study, minimum for A. grahami is 28–30 μM O 2 /g/h at 35 °C, which is c .…”

Land Cover, Land Use, and Climate Change Impacts on Endemic Cichlid Habitats in Northern Tanzania

“…The highest upper critical temperature (45.6 • C) recorded for a freshwater fish was for Alcolapia grahami (Boulenger 1912), from nearby Lake Magadi in Kenya [87], which is less than 3 • C warmer than the current upper range of the water temperature for the Natron Springs Alcolapia. The only other cichlids known to naturally inhabit similar temperatures are the endemic cichlids from the genus Danakilia, found in the shallow (<10 m) waters of Lake Abaeded in the Danakil Depression of Northern Eritrea and Lake Afrera in Ethiopia [88], and Iranochicla from Southern Iran [89].…”

“…The water in the lake itself is uninhabitable for fish to survive, even a short period of time. Therefore, if the temperature of the shallow springs surpasses their thermal tolerance or the water conditions are altered by future water abstraction [86,87], these fish have no migratory recourse. While the total area of the springs is estimated to be less than 10 km 2 , it is unknown how much of that is inhabited by the Alcolapia.…”