The contractile properties of swimming muscles have been investigated in marine teleosts from Antarctic (Trematomus lepidorhinus, Pseudochaenichthys georgianus), temperate (Pollachius virens, Limanda limanda, Agonis cataphractus, Callionymus lyra), and tropical (Abudefduf abdominalis, Thalassoma duperreyi) latitudes. Small bundles of fast twitch fibres were isolated from anterior myotomes and/or the pectoral fin adductor profundis muscle (m. add. p). Live fibre preparations were viable for several days at in vivo temperatures, but became progressively inexcitable at higher or lower temperatures. The stimulation frequency required to produce fused isometric tetani increased from 50 Hz in Antarctic species at 0-degrees-C to around 400 Hz in tropical species at 25-degrees-C. Maximum isometric tension (P(o)) was produced at the normal body temperature (NBT) of each species (Antarctic, 0-2-degrees-C; North Sea and Atlantic, 8-10-degrees-C; Indo-West Pacific, 23-25-degrees-C). P0 values at physiological temperatures (200-300 kN.m-2) were similar for Antarctic, temperate, and tropical species. A temperature induced "tension hysteresis" was observed in muscle fibres from some species. Exposure to < 0-degrees-C in Antarctic and < 2-degrees-C in temperate fish resulted in the temporary depression of tension over the whole experimental range, an effect reversed by incubation at higher temperatures. At normal body temperatures the halftimes for activation and relaxation of twitch and tetanic tension increased in the order Antarctic > temperate > tropical species. Relaxation was generally much slower at temperatures < 10-degrees-C in fibres from tropical than temperate fish. Q10 values for these parameters at NBTs were 1.3-2.1 for tropical species, 1.7-2.6 for temperate species, and 1.6-3.5 for Antarctic species. The force-velocity (P-V) relationship was studied in selected species using iso-velocity releases and the data below 0.8 P0 iteratively fitted to Hill's equation. The P-V relation at NBT was found to be significantly less curved in Antarctic than temperate species. The unloaded contraction velocity (V(max)) of fibres was positively correlated with NBT increasing from about 1 muscle fibre length.s-1 in an Antarctic fish (Trematomus lepidorhinus) at 1-degrees-C to around 16 muscle fibre lengths.s-1 in a tropical species (Thalassoma duperreyi) at 24-degrees-C. It is concluded that although muscle contraction in Antarctic fish shows adaptations for low temperature function, the degree of compensation achieved in shortening speed and twitch kinetics is relatively modest.
