WING-LOADING, STABILITY AND MORPHOMETRIC RELATIONSHIPS IN FLYING FISH (EXOCOETIDAE) FROM THE NORTH-EASTERN ATLANTIC

'Four-winged' flying fish (in which both pectoral and pelvic fins are hypertrophied) reach greater maximum sizes than 'two-winged' forms in which only the pectoral fins are enlarged. Exocoetus obtusirostris shows negatively allometric growth in relation to standard length in terms of body mass (b = 2.981), and lateral fin area (b = 1.834). In consequence, wing-loading rises in positive allometric fashion with standard length (b = 1.236). Pectoral fin length cannot be greater than 78-79% of standard length or swimming will be impaired, so the requirement for increased flying speed resulting from increased wing-loading during growth means that lift:drag ratios have to be improved by relatively narrowed wings and tapered wing tips; features which in turn increase wing-loading. Evidence is presented to show that hypertrophied pelvic fins in four-wingers are required to solve problems of stability in pitch, rather than to decrease wing-loading. The 'non-flying' flying fish, Oxyporhamphus micropterus, has very high wing-loadings, but the main reason that it cannot fly is that the centre of gravity of the fish is so far behind the pectoral fins that stalling on take-off would be inevitable. Flying fish possess reasonable quantities of red axial musculature, but no more than are used for cruising in fast-moving pelagic fish such as mackerel; it seems probable that acceleration to take-off speed in flying fish requires use of anaerobic white muscles.