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Abstract:The resilience of released hatchery-reared specimens increases with age and size, but production costs are also greater for these individuals. Therefore, for a given budget, the consequences of increasing age and size impose a trade-off between producing a large number of vulnerable (small) fish or a small number of resilient (large) fish. Once the optimal size for releasing fish has been defined, the choice of rearing protocol will determine the number and quality of the fish that can be released. In this study, different rearing protocols were compared using meagre juveniles (Argyrosomus regius), which are presently the target of a restocking programme conducted in the Balearic Islands (western Mediterranean). Seven different diets were compared during the grow-out phase to identify the diets that produced good-quality juveniles of a given size at the lowest cost. Most of the diets produced juveniles of suitable biological quality in terms of growth, fish condition (relationships between length and total weight, liver weight and mesenteric fat weight) and tissue biochemical composition. A semi-moist diet (Diet G) provided the best growth rate, closely followed by commercial meagre pellets (Diet A). In contrast, the cost of growing fish with Diet A was lower for any possible size at release. This study demonstrates the need to consider both growth rate and production cost to select the rearing protocol that maximizes the number of juveniles that can be produced for a given budget and desired release size. These considerations will ultimately increase the chance of success of restocking programmes.Keywords: Argyrosomus regius; restocking programme; production cost; fish quality; diet.La dieta usada en la cría puede determinar el éxito en la repoblación de peces: el caso de juveniles de corvina Argyrosomus regius criados en cautividad Resumen: La resiliencia de los ejemplares criados en cautividad y liberados se incrementa con la edad y el tamaño, pero los costes de producción también aumentan. Por lo tanto, para un presupuesto dado, estas consecuencias del incremento de la edad y el tamaño imponen un compromiso entre la producción de un gran número de peces vulnerables (pequeños) o un pequeño número de peces resistentes (grandes y de más edad). Una vez que el tamaño óptimo para la liberación de peces se ha definido, la elección del protocolo de cría determinará el número y la calidad de los peces que se pueden liberar con un presupuesto dado. En este estudio, se comparó la aplicación de diferentes protocolos de cría a juveniles de corvina (Argyrosomus regius), que es la especie objetivo de un programa de repoblación llevado a cabo en las Islas Baleares (Mediterráneo occidental). Se compararon siete dietas diferentes durante la fase de engorde para identificar cuáles de ellas podrían producir juveniles de buena calidad, de un tamaño dado y al menor coste. La mayoría de las dietas produjeron juveniles de calidad biológica adecuada en términos de crecimiento, condición del pez (estimada a partir de la rela...

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The Mediterranean spider crab, Maja squinado, is depleted due to overfishing. The crab has virtually disappeared from areas where it was abundant, such as the Balearic Islands and the Catalan coast. Maja squinado, is economically and ecologically very valuable, and it is essential to obtain information on its biology and rearing conditions to attempt to repopulate the damaged stocks of the species in the Mediterranean basin. Herein, we describe the first successful rearing of M. squinado under laboratory conditions. Our results show that M. squinado is an excellent candidate for restocking using cultured juveniles. Two consecutive broods with a 1–4 day interbrood period were observed in the laboratory in wild‐caught females, the maximum observed duration of embryonic development of the egg mass being 32 days at 18.4 ± 0.9°C, and went through four different stages. The complete larval and first juvenile development was studied in laboratory cultures fed enriched Artemia metanauplius. At 19.6 ± 0.6°C, development from hatching to first crab moult took 17 days, and it comprised two zoeae stages and one megalopa stage. The survival rate at the different stages was monitored, and 7.13 ± 2.3% was achieved at the first crab instar.

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