Does geometry limit squid growth?

Abstract

Pauly has argued for the generalization of von Bertalanffy growth models in fish, based on fundamental geometric relationships between surface area and volume. Recent evidence indicates growth curves of squids rise much more rapidly than those of fish, which appears to be in conflict with such geometric generalizations. Although the generalizations have recently been questioned even for fish, it remains important to establish that squid geometries differ greatly from those of fish. We measured key dimensions from a locomotory perspective in squid with masses from 100 μg paralarvae to 100 kg giants (nine orders of magnitude) and modelled their growth allometries. Elongation of the “hollow tubes” characterizing squid form, as well as increasing fin size contrasts with the relatively constant form of growing fish. When expressed as the dimensionless ratio of surface area 1/2 /volume 1/3 (the “Vogel number”) cod show a small decrease, whereas the ratio for squid increases two-fold over the range for which data is available. The consequences for growth are potentially large because squid respire directly through these surfaces.