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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. [ABSTRACT FROM AUTHOR]

Accurate age estimates for fish are critical for properly understanding stock dynamics and health; this is particularly true for larger billfishes. Here we determined the most accurate aging estimation methods for swordfish (Xiphias gladius). We compared age estimates obtained from fin‐ray sections, otolith sections, whole otoliths, and vertebrae collected from 87 swordfish off the east coast of Corsica. Age estimates from otolith sections were most consistently estimated across different readers (lowest average percentage error), followed by fin‐ray sections, third vertebrae, and whole otoliths. When the age estimates from the otolith sections were compared with the other three age sclerochronological methods, we found the average percentage error to be lowest between the otolith section and fin‐ray methods. However, age estimates from fin rays proved most useful for estimating swordfish younger than 6 years, as the fin ray‐based age diverged from that of the otolith sections as the swordfish aged. Combining fin ray and otolith section techniques, we estimated the growth parameters of 1–12‐year‐old females (L∞ = 259.412, k = 0.113, t0 = −2.499) and 1–7‐year‐old males (L∞ = 175.543, k = 0.202, t0 = −2.239). We found that females grew significantly faster than males after 3 years and remained larger thereafter. Our calculated growth rates for this region of the north‐western Mediterranean Sea were lower than those of the Atlantic, Pacific, and eastern Mediterranean Sea swordfish populations, and similar to growth rates recorded for the western Mediterranean Sea populations. Our study provides critical knowledge on biological‐related parameters to serve as a guide for preserving the swordfish population in the Mediterranean Sea. [ABSTRACT FROM AUTHOR]

An extensive survey of macroparasites in 320 European eel Anguilla anguilla (Linnaeus, 1758) was conducted in two brackish lagoons and eleven freshwater localities in the Mediterranean island of Corsica (France) between spring 2021 and winter 2021–2022. It resulted in the identification of nineteen parasites: two Monogea, four Digenea, one Copepoda, four Acanthocephala, three Cestoda, and five Nematoda, including the first geographical records, as Corsican freshwater sites were studied for the first time. The silvering stage was determined, and the eels were aged through otolithometry to compare parasite communities. Classic parasitology indices, a multivariate analysis, and an analysis of indicator values (IndVal) showed clear preferences towards the host's habitat and salinity. Seasonal variations were shown for several parasites. A dataset from the same two coastal lagoons was used to study the changes in the parasite communities over the last decade, and this showed an increase in the prevalence and abundance of three invasive helminth species: the Monogenea Pseudodactylogyrus bini (Kikuchi, 1929), Pseudodactylogyrus anguillae (Yin and Sproston, 1948) Gusev, 1965 and the Nematoda Anguillicola crassus Kuwahara, Niimi, and Itagaki, 1974. These pathogenic parasites were found in all sampled localities, except for the two Monogenea in the polyhaline-to-euhaline Urbino lagoon. It is thus advised that future management measures take into account the environmental preferences of the most concerning parasites. [ABSTRACT FROM AUTHOR]