Thunniform swimming: muscle dynamics and mechanical power production of aerobic fibres in yellowfin tuna (Thunnus albacares)

Abstract

SUMMARYWe studied the mechanical properties of deep red aerobic muscle of yellowfin tuna (Thunnus albacares), using both in vivo and in vitro methods. In fish swimming in a water tunnel at 1-3·L·s -1 (where L is fork length), muscle length changes were recorded by sonomicrometry, and activation timing was quantified by electromyography. In some fish a tendon buckle was also implanted on the caudal tendon to measure instantaneous muscle forces transmitted to the tail. Between measurement sites at 0.45 to 0.65·L, the wave of muscle shortening progressed along the body at a relatively high velocity of 1.7·L per tail beat period, and a significant phase shift (31±4°) occurred between muscle shortening and local midline curvature, both suggesting red muscle power is directed posteriorly, rather than causing local body bending, which is a hallmark of thunniform swimming. Muscle activation at 0.53·L was initiated at about 50° of the tail beat period and ceased at about 160°, where 90°is peak muscle length and 180° is minimum length. Strain amplitude in the deep red fibres at 0.5·L was ±5.4%, double that predicted from midline curvature analysis. Work and power production were measured in isolated bundles of red fibres from 0.5·L by the work loop technique. Power was maximal at 3-4·Hz and fell to less than 50% of maximum after 6·Hz. Based on the timing of activation, muscle strain, tail beat frequencies and forces in the caudal tendon while swimming, we conclude that yellowfin tuna, like skipjack, use their red muscles under conditions that produce near-maximal power output while swimming. Interestingly, the red muscles of yellowfin tuna are slower than those of skipjack, which corresponds with the slower tail beat frequencies and cruising speeds in yellowfin.

Red muscle function in stiff-bodied swimmers: there and almost back again

“…Comparison of twitch kinetics from muscle of similar-sized yellowfin and skipjack tuna confirms the expectation that slower tail-beat frequencies during swimming in yellowfin tuna are accompanied by red muscles with slower contraction kinetics, both the twitch and cycle frequency for maximal power production [16,26]. Said another way, fishes that swim more slowly have muscles that are slower, in spite of being warm.…”

“…Data from Donley et al [13] and Katz et al [15]. function at optimal strain for maximal power output during swimming in tunas [16,26]. This has not yet been tested in sharks with internalized muscles and would be very valuable to know.…”

The length-force behavior and operating length range of squid muscle varies as a function of position in the mantle wall

“…Thus, fibers from a given region of the mantle wall may produce different instantaneous forces than those in other regions. Such transmural differences in force output by the circular fibers could reduce the mechanical efficiency of the mantle during contraction (Shadwick and Syme, 2008;van Leeuwen et al, 2008).…”

Integrating gastrocnemius force-length properties,in vivoactivation, and operating lengths reveals howAnolisdeal with ecological challenges

“…Linking kinematics (i.e. curvature of the midline) with muscle lengths has proven useful for studying muscle function in swimming fishes Shadwick et al, 1998;Donley and Shadwick, 2003), although this relationship becomes decoupled in lamnid/thunniform swimmers that have a different muscle/tendon arrangement (Donley et al, 2005;Shadwick and Syme, 2008).…”