Morphometry Of The Gills Of The Elasmobranch Scyliorhinus Stellaris In Relation To Body Size

Abstract

ABSTRACT In order to study the dependence of the dimensions of the respiratory apparatus on body size and to provide a morphometric basis for the analysis of branchial gas exchange function, the gills of 12 specimens of Scyliorhinus stellaris L., weighing 0·58–2·62 kg, were examined morphometrically. The average values and the local variations of the structural parameters determining diffusive gas transfer properties of the gills were determined. Particular attention was paid to corrections for shrinkage effects in surface area measurements and to corrections for the Holmes and slant effects in measurements of paraffin sections. The shape and size of secondary lamellae varied according to the sampling site on the filament, and filament length varied with its location on the gill arch. Also the water-blood distance varied, mainly because of frequent occurrence of thickenings at mid-height of the secondary lamellae. The total gill surface area increased proportionally to (body mass)0·78, mainly because of an increase in surface area of individual lamellae rather than an increase in their number. Since the thickness of the secondary lamellae varied little with body mass, the observed increase in total filament length in proportion to body mass is attributed to an increase in interlamellar distance. The water-blood distance varied little with body mass. The extent of shrinkage was found to be about 10% of filament length, but because of the compensating increase in secondary lamellar frequency this had no effect on gill area estimates, although it did affect the interlamellar dimensions. Shrinkage of individual secondary lamellae was extremely difficult to estimate, partly because of non-isometric shrinkage within the gill system. Underestimation of secondary lamellar area using paraffin sections could approach 30% mainly because of a reduction in the proportion of the pillar cell system exposed above the level of the gill filaments.