The Development of Form and Function in Fishes and the Question of Larval Adaptation

Allometric Growth in Fish Larvae: Timing and Function

Jan W. M. Osse and Jos G. M. Van den Boogaart

doi: https://doi.org/10.47886/9781888569582.ch8

Abstract.—This paper examines how allometric analysis can be used as a tool to explain morphological changes that take place during fish larval development. First, constraints to survival, growth, and continued differentiation are identified. Then, processes of growth are predicted to meet and overcome these constraints, which are mutually interrelated. The final step is to test the predictions by looking at growth of the entire animal and at separate elements belonging to particular functional systems. The reproductive strategy of producing numerous, but very small eggs, adopted by many teleosts, has major implications. In particular, the lack of reserves, the need to utilize external food early in life, and the extreme susceptibility of newly hatched larvae to predation put them under strong selective pressure to grow rapidly. Small size also means that viscous forces are much more important than they are at bigger size later in life. When energy is limited, larvae should direct available resources towards primary needs yielding the greatest return in terms of enhancing the larva’s ability to find, capture, and assimilate additional food and to avoid being eaten. We speculate that constructions for feeding, swimming, and ventilation are particularly important and should therefore grow early and at a higher rate than the body as a whole. Allometric data of a wide variety of species and taken from several functional complexes are presented to support this contention. Length dependent changing growth coefficients of head, trunk, and tail indeed show the predicted priorities in different major groups of fish. High positive allometric growth of structures involved in feeding make early larvae specialized zooplanktivorous predators.