Otolith shape analysis and daily increment validation during ontogeny of larval and juvenile European chub Squalius cephalus

Abstract

This assesses features of otoliths from laboratory‐reared embryos, larvae and juvenile European chub Squalius cephalus from hatching to 180 days post‐hatching (dph). We observed the development of the three pairs of otoliths (lapilli, sagittae and asterisci) and more precisely shape changes, as well as timing and deposition rate of increments of the lapilli. The lapilli and the sagittae were present at hatching, whereas the asterisci formed between 20 and 30 dph. The lapillus and sagitta shapes were round until 20 dph. From 60 dph the anterior and the posterior rostra of the sagittae were well developed, but very thin, making this otolith too fragile to manipulate for further studies of shape and validation of otolith increment deposition rate. The lapilli provided reliable age estimates for free embryos, larvae and juveniles up to 120 dph. However, caution should be taken when ageing fish older than 150 dph as an underestimation was noticeable. The regression of the number of otolith increments on age showed a slope and an intercept not significantly different from 1 and 0, respectively, which indicated that otolith growth increments were deposited on a daily basis, with the first microincrement occurring at hatching. Increment counts were consistent between three interpreters, indicating a consistent and reliable age estimate. This study validates that the otolith increment deposition rate can be used to assess hatching dates and daily growth of wild S. cephalus under 150 dph and in environments similar to the conditions used in this study.

Spawning areas and migration patterns in the early life history of Squalius cephalus (Linnaeus, 1758): Use of otolith microchemistry for conservation and sustainable management

“…Following the recommendations of Bounket et al (2019), only lapilli were extracted, cleaned and stored dry in cryotubes for further analyses. Only the right‐side otoliths were used in this study.…”

“…According to previous validation of daily growth increments in S. cephalus otoliths (Bounket et al, 2019) photographs of the sectioned otolith were taken along the anterior axis (rostrum tip) and were merged into a large image using Photostitch software (Canon; www.canon‐utilities‐photostitch.en.lo4d.com). A unique reading transect following the maximum growth axis was drawn on each stitched image.…”

The Interannual Variability of the Fall Size of Young-of-The-Year Chub (Squalius cephalus): Influence of Phenology, Growth Patterns and Abiotic Factors

“…The size classes (TL) of the collected individuals were ranged between 20 and 80 mm. The lapilli, the most appropriate otoliths in cyprinid species to assess fish growth (Bounket et al, 2019), were extracted, immediately cleaned in distilled water and placed to dry in plastic tubes.…”

“…Each otolith was observed and digitized at ×1,000 magnification using a light microscope (Leica DM 2500, Solms, Germany) combined with a camera (Leica MC 170HD). Age was estimated by counting the daily increments (Bounket et al, 2019) between the hatching check and the edge of the otolith along the maximum growth axis from the core to the anterior face. The hatching check was similar to those previously observed in other cyprinids (Smith and Walker, 2003;Li et al, 2009).…”

“…The first two steps consist in estimating the size of the fish at the first increment, L 0p , and the size of the radius at the first increment, R 0p . These two parameters are biological intercepts and were determined from a controlled experiment (Bounket et al, 2019). The third and fourth steps consist in determining whether the relationship between otolith radii and fish sizes is allometric or isometric and were performed independently for each section/ year.…”