Successful aquacultural production of juvenile fish requires that the optimal rearing conditions be applied. However, for many fish species, there is a significant knowledge gap concerning these conditions. In this study, we evaluated the effects of stocking density on the survival and growth of brown meagre, Sciaena umbra (L.), during rearing trials in an experimental hatchery. This research forms part of a feasibility project to improve the aquacultural production of brown meagre. Four initial larval density treatments (5, 10, 30, and 70 larvae per L) were established. At 0, 9, 17, 22, and 25 days post-hatching, we measured the total length, coefficient of variation in length, and specific growth rate. The physicochemical water parameters remained at satisfactory levels for fish culture throughout the experiment. Lower densities promoted better growth in terms of total length, specific growth rate, and survival. We observed a significant negative correlation between larval density and length growth/survival. Thus, the low larval density treatment yielded the highest survival (48.5% ± 3.46%), growth in final total length (11.9 ± 1.09 mm), and specific growth rate (5.13% ± 0.39% per day). Increased stocking density therefore negatively affects growth and survival, reduces homogeneity, but increases the production of S. umbra larvae. This study helps identify optimal aquaculture conditions for maximizing the production of juvenile S. umbra for ecological restoration.

The demand for the purple sea urchin Paracentrotus lividus has led to the decline of its wild populations, increasing interest in cultivating this species for commercial purposes and ecological restoration purposes. Consequently, there is a need to expand knowledge about the optimal conditions for sea urchin aquaculture, particularly regarding food regimes. Here, we evaluate the effects of several vegetable diets on the survival and growth of early juveniles of P. lividus. Using an outdoor experimental assay, we fed early juveniles (5–6.5 mm) various diets: fresh algae (Ulva sp.), aquaculture pellets, and vegetables (carrot, spinach, and maize) presented as individual or mixed diets (equal mass proportions). All diets were provided ad libitum in equal mass proportions. After 120 days, the pellet‐fed urchins showed good growth but a high mortality rate (>40%). The Ulva sp. diet, considered the control regime mimicking wild sea urchin diet, resulted in low mortality but poor growth performance (maximum of 10.92 ± 1.94 mm in diameter and 0.68 ± 0.26 g in weight). In contrast, plant‐based diets, especially those containing maize, led to the highest growth and lowest mortality rates (<5%). Notably, the triple mixed diet (carrot–spinach–maize) resulted in a threefold size increase, as the P. lividus juveniles reached 15 mm in 4 months. This study demonstrates the effectiveness of inexpensive, ready‐to‐use vegetable‐based diets in optimizing rearing protocols for early juveniles of P. lividus. It offers preliminary insights into dietary preferences to rapidly attain an adequate release size for purple urchin aimed at restocking wild populations and balancing aquaculture and ecological restoration needs.

Dentex dentex and Sciaena umbra are two coastal fish species inhabiting Mediterranean waters, where they are considered threatened (assessed as ‘Vulnerable’ on the IUCN Red List). With increased knowledge of both species reproduction, they are envisioned as potential candidate species for restocking purposes around Corsica. However, such actions require genetic monitoring of juveniles that aimed to be released in order to make sure that restocking could not alter the natural genetic diversity. This study aimed to investigate microsatellite gene diversity of hatchery‐reared D. dentex and S. umbra juveniles (8 and 11 microsatellite markers, respectively), compared to wild Corsican populations. In each species, broodstock genetic diversity turned out to be quite representative of wild populations. However, this study highlighted that the effective number of breeders was very small in S. umbra (29% of the broodstock participated in juveniles' production) and was composed of dominant parents (i.e., higher contribution of these parents to juvenile production) in D. dentex (one male and one female produced the majority of the juvenile sample). This led to heterozygote excess in juvenile samples and a significant genetic differentiation between (i) juvenile and wild samples and (ii) juvenile and broodstock samples, in both species. Broodstock individuals used in this study were fished in the wild, which was proven here not be sufficient for maintaining the level of genetic diversity found in natural populations. This study highlighted the idea that husbandry production might induce genetic distortion and therefore that genetic controls on hatchery‐produced juveniles are essential for restocking purposes.

The brown meagre, Sciaena umbra, is an IUCN red-listed Vulnerable teleost in the Mediterranean Sea. To potentially consider restocking these populations, it is crucial to identify rearing and release protocol parameters that could maximize in situ survival. In this context, investigating the effects of body size and habitat enrichment in rearing tanks on behavioural responses and individual performances, both of which are linked to survival capacities, appears highly relevant. Therefore, this study examined the effects of rearing environment (enriched vs bare tanks) and body size (30-80 mm total length) on boldness, exploratory behaviour, and escape performance in hatchery-reared S. umbra juveniles. Rearing environment had no significant effect on any of the variables studied. However, the experimental tests performed revealed significant size-dependent variations: smaller juveniles exhibited higher boldness, exploration tendencies and escape performance (e.g. with shorter latency and higher responsiveness) compared to larger individuals. Conversely, larger juveniles seemed to display lower risk-taking tendencies, potentially reflecting ontogenetic shifts toward sedentary, adult-like behaviors. These findings suggest that intermediate size classes (e.g. 50-60 mm) may offer the best trade-off for restocking, balancing predation avoidance and dispersal potential. This study provides critical insights for designing effective restocking protocols for S. umbra, emphasizing notably the need to consider size-specific behaviors and performances during early juvenile development.