The role of extrinsic variation—cohabiting juvenile fish species exhibit similar otolith elemental signatures

The effect of extrinsic (environmentally based) and intrinsic (physiologically based) controls on otolith elemental signatures remains poorly understood. We evaluated the relative importance of both extrinsic and intrinsic factors using juvenile fish in Eastern Tropical Pacific (ETP) mangroves. To assess extrinsic influences, we compared the cohabiting yellow snapper Lutjanus argentiventris and sailfin grouper Mycteroperca olfax from the Galápagos Archipelago. To evaluate intrinsic influences, we compared yellow snapper from the Gulf of California (Mexico) and the Galápagos Archipelago (Ecuador). The 2 cohabiting species in the Galápagos exhibited very similar otolith elemental signatures, with no significant differences observed for Li, Cu, Mg, Mn, Rb, and Sr (univariate ANOVAs, p > 0.05), and a small separation achieved between these species (ANOSIM test, R = 0.01, p = 0.038). The yellow snappers from Galápagos and the Gulf of California exhibited distinct elemental signatures increasing from Rb, Cu, Mn, Sr, Li to Ba (univariate ANOVAs, p < 0.05), with a large separation between them (ANOSIM test, R = 0.55, p = 0.001). The present study suggests that extrinsic factors (e.g. water chemistry, temperature, salinity) can be more important than intrinsic factors (e.g. physiology, growth rates, genetics) for influencing elemental uptake in the otoliths of juveniles from mangrove waters. However, improved understanding of factors influencing elemental incorporation is still needed to ensure accurate interpretation of field data, especially in dynamic oceanographic systems, which is the case for both the Gulf of California and the Galápagos Archipelago.

Morphology and morphometric relationships for sagitta otoliths in Lutjanus argentiventris (Pisces: Lutjanidae) and Hyporthodus acanthistius (Pisces: Serranidae) from the Colombian Pacific Ocean

Fish earstones, or otoliths, are inner ear structures that can be studied to determine a fish’s age and are a source of taxonomically informative data. In the present work, sagitta otoliths of the Yellowtail snapper (Lutjanus argentiventris) and the Red grouper (Hyporthodus acanthistius) were collected in the Colombian Pacific, and their key morphological features were studied. Otoliths of the Yellow tail snapper were distinctly concave by their distal surface, revealing features shared with species of its genus (Lutjanus). Red grouper otoliths were elliptic and compressed laterally by their proximal surface, bearing similarities to those of other Serranid species. Morphometric relationships between otolith size weight and whole fish size and weight were also studied. In Red groupers significant statistical morphometric relationships between otolith and body features were found via power regression models; successfully relating otolith length with total fish length, otolith weight with total fish length, otolith length with total fish weight, and otolith weight with total fish weight. No significant morphometric relationships were found for the Yellow snapper data. In both fish species, otolith transversal sections proved best to identify its internal features and to distinguish otolith growth rings, as a method for determining the specimen’s age.