Thermal dependence of contractile properties of single skinned muscle fibres from Antarctic and various warm water marine fishes including Skipjack Tuna (Katsuwonus pelamis) and Kawakawa (Euthynnus affinis)
Single fast fibres and small bundles of slow fibres were isolated from the trunk muscles of an Antarctic (Notothenia neglecta) and various warm water marine fishes (Blue Crevally,Carangus melampygus; Grey Mullet,Mugil cephalus; Dolphin Fish,Coryphaena hippurus; Skipjack-tuna,Katsuwonus pelamis and Kawakawa,Euthynuus affinis). Fibres were chemically skinned with the nonionic detergent Brij 58. For warm water species, maximum Ca2+-activated tension (P0) almost doubled between 5–20°C with little further increase up to 30°C. However, when measured at their normal body temperatures,P0 values for fast fibres were similar for all species examined, 15.7–22.5 N · cm−2. Ca2+-regulation of contraction was disrupted at temperatures above 15°C in the Antarctic species, but was maintained at up to 30°C for warm water fish. Unloaded (maximum) contraction speeds (Vmax) of fibres were determined by the “slacktest” method. In general,Vmax was approximately two times higher in white than red muscles for all species studied, except Skipjack tuna. For Skipjack tuna,Vmax of superficial red and white fibres was similar (15.7 muscle lengths · s−1 (L0 · s−1)) but were 6.5 times faster than theVmax of internal red muscle fibres (2.4±0.2L0 · s−1) (25°C). Vmax forN. neglecta fast fibres at 0–5°C (2–3L0 · s−1) were similar to that of warm water species measured at 10–20°C. However, when measured at their normal muscle temperatures, theVmax for the fast muscle fibres of the warm water species were 2–3 times higher than that forN. neglecta. In general,Q10(15–30°C) values forVmax were in the range 1.8–2.0 for all warm water species studied except Skipjack tuna.Vmax for the internal red muscle fibres of Skipjack tuna were much more temperature dependent (Q10(15–30°C)=3.1) (P<0.01) than for superficial red or white muscle fibres. The proportion of slower red muscle fibres in tuna (28% for 1 kg Skipjack) is 3–10 times higher than for most teleosts and is related to the tuna's need to sustain high cruising speeds. We suggest that the 8–10°C temperature gradient that can exist in Skipjack tuna between internal red and white muscles allows both fibre types to contract at the same speed. Therefore, in tuna, both red and white muscle may contribute to power generation during high speed swimming.