Ontogenetic and environmental effects on otolith shape variability in three Mediterranean European eel (Anguilla anguilla, L.) local stocks

Abstract

Otolith morphology is an efficient tool for the discrimination of fish stocks, populations and species when comparative genetic data are not available. Currently, the relationship between environmental factors and otolith shape is poorly characterized for the European eel (Anguilla anguilla), a highly migratory catadromous species constituting a single, randomly mating stock. The present study analyses the differences in otolith morphology between three Mediterranean eel local stocks from different environmental contexts (i.e. two brackish lagoons and one river). The relationship between otolith shape and otolith size was studied by means of Elliptic Fourier analysis and multivariate statistics. Otolith profile was digitally acquired and Cartesian coordinates were extracted. Partial Least Square (PLS) analysis pointed to continuous allometric growth in size and shape in otoliths from all three sites. In the three environments, shape variations occurred during growth as indicated by the presence of a significant and positive relationship between otolith size and the first PLS latent vector (i.e. which bears most of the information regarding otolith outline). Differences between smaller and larger sized otoliths were investigated using PLS Discriminant Analysis (PLSDA) and cluster analysis. Results indicate that otolith shape is highly uniform at smaller than at larger sizes. These shape differences apparently overlap the initial differentiation of the small otolith outlines acquired by eels during the growing phase as elvers in the marine environment. Data were discussed considering that the physical and chemical habitat variability in brackish lagoons and river could underlie a marked change in otolith shape during the animals' growth.

Otolith shape variation provides a marker of stock origin for north Atlantic bluefin tuna (Thunnus thynnus)

“…The strong effect of fish length on otolith shape variation in Atlantic bluefin tuna is not surprising and has been reported in many other species (Smith 1992;Mérigot et al 2007;Capoccioni et al 2011). The relationship between fish size and otolith shape reflects the combined effects of ontogeny and the environment on otolith shape (Vignon 2012).…”

Stock discrimination of two insular populations of Diplodus annularis (Actinopterygii: Perciformes: Sparidae) along the coast of Tunisia by analysis of otolith shape

“…are almost certainly the cause of geographic variations in the shape or appearance of the otolith nucleus, otolith annuli, and variations in the ratio of otolith size to fi sh size (Cañás et al 2012). However, the measurements of otolith shape based on ratios of otolith radii and on the Fourier analyses in particular, had some success in distinguishing among stocks and have been assumed to be based, at least in part, on genetic differences (Capoccioni et al 2011). In some cases, reports of stock discrimination based on otoliths morphology appear to refl ect environmental differences among regions (Rakocinski et al 2015).…”

Phenotypic plasticity in wild marine fishes associated with fish-cage aquaculture

“…These data suggest that the effect of the intake of food pellets on otoliths may be influenced by fish age, since the bogues sampled were old specimens (Monteiro et al, 2006) in comparison to younger specimens of salema (Méndez-Villamil et al, 2002). The presence of otolith morphs within a population has been described already in other wild fish (Panfili et al, 1990;Gagliano & McCormick, 2004;DuarteNeto et al, 2008;Capoccioni et al, 2011). In many cases, this is a response to different growth rates, where the larger otoliths (morphotype I) grow faster than smaller ones (morphotype II).…”