Short‐term thermal acclimation induces adaptive changes in the inner mitochondrial membranes of fish skeletal muscle

Abstract

In the oxidative muscles (musculi laterales superficiales) of crucian carp Carassius carassius acclimated for 6 weeks to either 5 or 25° C, the volume density and the surface density of fibres per tissue did not differ significantly between the control and experimental groups. The correlation ratio (μ2) for these values was below 50, 39·3 and 43·9 respectively. After acclimation to 5° C, the surface density of outer mitochondrial membrane per fibre increased significantly from 0·93 to 1·23m2 cm−3 in the summer population but dropped from 0·94 to 0·67 m2 cm−3 in the winter population. The surface density of outer mitochondrial membrane per mitochondrion increased from 3·24 to 4·52 m2 cm−3 in summer fish. After acclimation to 25° C, the surface density of inner mitochondrial membranes per muscle fibre decreased from 4·04 to 1·79 m2 cm−3 in summer fish and from 3·86 to 1·07 m2 cm−3 in winter fish. The surface density of inner mitochondrial membranes per mitochondrion increased from 14·17 to 15·60 m2cm−3 in summer fish but dropped from 13·91 to 10·67 m2 cm−3 in winter fish. Correlation matrices demonstrate a negative correlation of the surface density of outer mitochondrial membrane per mitochondrion with the volume density of mitochondria per fibre and temperature, suggesting cold‐induced proliferation of small mitochondria. It was concluded that short‐term cold acclimation increased surface area of the inner mitochondrial membranes in summer fish.