Experimental validation of otolith-based age and growth reconstructions across multiple life stages of a critically endangered estuarine fish

Abstract

Background The application of otolith-based tools to inform the management and conservation of fishes first requires taxon- and stage-specific validation. The Delta Smelt (Hypomesus transpacificus), a critically endangered estuarine fish that is endemic to the upper San Francisco Estuary (SFE), California, United States, serves as a key indicator species in the SFE; thus, understanding this species’ vital rates and population dynamics is valuable for assessing the overall health of the estuary. Otolith-based tools have been developed and applied across multiple life stages of Delta Smelt to reconstruct age structure, growth, phenology, and migration. However, key methodological assumptions have yet to be validated, thus limiting confidence in otolith-derived metrics that are important for informing major water management decisions in the SFE. Methods Using known-age cultured Delta Smelt and multiple independent otolith analysts, we examined otolith formation, otolith-somatic proportionality, aging accuracy and precision, left-right symmetry, and the effects of image magnification for larval, juvenile, and adult Delta Smelt. Results Overall, otolith size varied linearly with fish size (from 10–60 mm), explaining 99% of the variation in fish length, despite a unique slope for larvae < 10 mm. Otolith-somatic proportionality was similar among wild and cultured specimens. Aging precision among independent analysts was 98% and aging accuracy relative to known ages was 96%, with age estimates exhibiting negligible differences among left and right otoliths. Though error generally increased with age, percent error decreased from 0–30 days-post-hatch, with precision remaining relatively high (≥ 95%) thereafter. Increased magnification (400×) further improved aging accuracy for the oldest, slowest-growing individuals. Together, these results indicate that otolith-based techniques provide reliable age and growth reconstructions for larval, juvenile, and adult Delta Smelt. Such experimental assessments across multiple developmental stages are key steps toward assessing confidence in otolith-derived metrics that are often used to assess the dynamics of wild fish populations.

Allometric model of brain morphology of Hemiculter leucisculus and its variation along climatic gradients

“…Lapillus has paired calcium carbonate structures found in oval sacs in the inner ear of teleost, which are often used to identify the age of cyprinid fishes (Horwitz et al, 2018; Li et al, 2015; Xieu et al, 2021). We used the lapillus to identify the age of fish according to Wang et al (2013), with minor changes.…”

“…The brain has always been an important region of interest in all biological fields related to animals due to its important role in almost all connections between individual organisms and their environments (Gonda et al, 2013). The brain is also a complex organ (Hoops et al, 2017), typically consisting of six main regions in fishes: olfactory bulbs, telencephalon, mesencephalon (composed of the optic tectum and tegmentum), diencephalon (composed partially of the hypothalamus), cerebellum, and medulla oblongata (Oliveira et al, 2008;Simões et al, 2012;Wang, 1986;Xie, 2010). In studies, researchers often selected five regions (olfactory bulbs, telencephalic lobes, optic tectum, corpus cerebelli, and hypothalamus) for analysis, because these brain regions play an important role in ecological interactions, and their morphology is distinct and measurable (Edmunds et al, 2016).…”

“…The optic tectum is formed by the dorsal midbrain (Dong et al, 2001), and is prominent and well corticalised (Nguyên et al, 2001). It is considered not only the main visual center (Northmore, 1981) but also thought to govern certain movement patterns of fishes (Xie, 2010). The corpus cerebelli is located caudal to the optic tectum (Wang, 1986), and is related to motor control (Paulin, 1993), cognitive, and emotional function (Lalonde & Botez, 1990;Rodriguez et al, 2005).…”

Wakasagi in the San Francisco Bay Delta Watershed: Comparative Trends in Distribution and Life-History Traits with Native Delta Smelt

“…Otoliths were processed and analyzed following established protocols (Hobbs et al 2007;Hobbs et al 2019;Xieu et al 2021). In short, sagittal otoliths were dissected from the cranium of each fish using Dupont® SE140 ultra-fine forceps and stored dry in tissue culture trays.…”

Visual, spectral, and microchemical quantification of crystalline anomalies in otoliths of wild and cultured delta smelt

“…1, Table 1), with fish containing a broken or missing otolith being previously excluded (n = 16). Image analysis was used to quantify several otolith metrics using ImageJ (Version 2.0) 50,51 . Differences in the size of left and right otoliths were used to estimate otolith asymmetry for each fish following Eq.…”