Feeding variations and shape changes of a temperate reef clingfish during its early ontogeny

The majority of rocky reef fishes have complex life cycles, involving transition from a pelagic to a benthic environment. This means that as they grow, their morphology, behaviour and feeding habits must change. Therefore, shape changes occurring during early development of these fishes will be related to diet changes. The clingfish Sicyases sanguineus was selected for this study, because it displays a noticeable variation in shape from pelagic larvae to juvenile stage, and it is expected that diet composition will change as well. The pattern of shape changes was studied using geometric morphometrics. A set of 9 landmarks were digitized in 159 larval and juvenile fish and the same specimens were used for gut content analysis. Allometric growth was most prominent early in the ontogeny, from 4 to 12 mm. Morphology changed from a thin and hydrodynamic shape to a more robust and deeper body prior to settlement. The diet of the clingfish during larval stages showed preferences for a variety of copepod stages. As individual grows the ingested prey volume increases, but not the number and width of prey. A partial least square analysis showed low covariance between shape changes and diet composition changes in prey number and volume, suggesting that the two processes were temporally decoupled. The biggest shape changes, a lengthening of the visceral cavity and a flattening of the head, occurred up to 12 mm standard length, while the largest feeding differentiation, shifting from copepods to microalgae, occurred after 16 mm. Results suggest that shape changes precede trophic changes in this clingfish species during the transition from a pelagic to a benthic habitat.