Abstract
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.
Highlights
Most coral and rocky reef fishes have stagestructured life histories with two main distinct stages including a pelagic larval stage and a demersal stage
The settlement phase, which is the transition from the pelagic environment to the benthic reef environment is a key period, because during this phase fish often undergo a change in form and physiology to a mode suited for the new environment (McCormick and Makey 1997), which produces changes in behaviour and feeding habits (Russo et al 2007, Frédérich et al 2008, 2012, Usmar 2012)
Procrustes ANOVA indicates that measurement error was 1.91% (Table 1)
Summary
Most coral and rocky reef fishes have stagestructured life histories with two main distinct stages including a pelagic larval stage and a demersal stage (generally juveniles and adults; Gonçalves et al 2002, Lecchini 2005, Hernández-Miranda et al 2009). Fish morphology plays a major role in determining diet, because variations in morphology are assumed to underlie variation in feeding ability, and variation in the latter is expected to affect diet (Wainwright and Richard 1995). Body size is important in diet shifts of fishes; as individuals grow, their feeding habits change. The shape of the feeding apparatus changes throughout early development, and morphology plays a central role in determining the minimal, maximal and optimal prey sizes (Wainwright and Richard 1995)
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