ABSTRACT
But increased energy expenditure is not the only drawback to keeping aloft in the water by generating dynamic lift. Dense fishes must maintain a minimum forward cruising speed to generate enough lift to prevent them sinking, so they cannot hover or swim backward. The swimming rhythms of spinal sharks (35-40 tail beats min-1 in spinal Scyliorhinus, see p. 356) are apparently just below this minimum swimming speed. For benthic fishes that rest on the bottom and only swim occasionally, dynamic lift generation is appropriate, but, for other fishes, a better solution would seem at first sight to be the storage of light materials to provide static lift (as do airships and submarines) and thus avoid the drawbacks of continually generating dynamic lift. But little is as it seems at first sight, and since there are many superbly adapted pelagic fishes such as tunas that rely solely on dynamic lift, static lift is not the best solution for all, and even those that adopt it require to “invent” remarkable tricks to surmount the problems involved with static lift.
