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The reproductive parameters of the dusky grouper, Epinephelus marginatus, in the Balearic Islands (western Mediterranean) were studied with a histological analysis of specimens caught by artisanal and recreational spear fisheries. The histological examination of the gonads showed that the dusky grouper spawning season extends from late spring to the end of summer with clear spawning peaks in July and August. The monthly variation of the hepatosomatic index (HSI) and the Le Cren condition index suggests that reserves for gonad development were obtained from the energy stored in the liver before spawning. Females reach maturation at 49 cm total length (TL) and 6 years, and transitional individuals start to occur before all females are matured. Males were the largest and oldest specimens but females were also present in the largest and oldest classes and there was a large sex, size and age overlap in the population. The fecundity data showed that the dusky grouper is a determinate spawner with asynchronous oocyte development. Potential fecundity ranged between 65 thousand and 8 million oocytes in females from 39 to 92 cm TL and from 6 to 42 years of age, with a mean relative fecundity of 334 x 103 oocytes kg-1. Females spawn an average of 10 batches during the spawning season, with a relative batch fecundity of 75 x 103 oocytes kg-1. Fecundity increased significantly with length, weight, age and HSI, while relative fecundity was only related to HSI. Based on the results obtained in the present study (long reproductive lifespan of females, influence of maternal attributes on fecundity and size at maturity) management measures for the species were evaluated.

In this study, we used microsatellite markers to examine the genetic structures of Centropomus undecimalis (Bloch, 1792) and Epinephelus marginatus (Lowe, 1834) populations collected from artisanal fishing sites along a stretch of coastline in southeastern Brazil. Based on F-statistics, there was no significant genetic differentiation evident in any C. undecimalis samples (FST=0.012). However, Bayesian clustering, principal component analysis (PCA) and discriminant analysis of principal components (DAPC) results suggested that there were most likely two clusters, with no relation to geographic areas. The bottleneck results showed no significant values and the effective population sizes (Ne) for the two genetically differentiated groups were large and similar. In contrast, for E. marginatus populations, the microsatellite loci showed no population subdivisions. The FST value was low and non-significant (FST=0.008), a Bayesian analysis indicated one cluster, and a PCA showed that all samples from different geographical sites shared the same genetic structure. The bottleneck results exhibited significant differences, and a low Ne was observed. The results of the genetic study of these two species along the southeastern Brazilian coast suggest that the distinct genetic structure of each species should be taken into account as management units for the conservation of their genetic diversities. En este estudio se han utilizado marcadores microsatélites para examinar la estructura genética de Centropomus undecimalis (Bloch, 1792) y Epinephelus marginatus (Lowe, 1834) en localidades de pesca artesanal localizadas a lo largo de la costa del sudeste de Brasil. Los estadísticos de diferenciación poblacional (F-statisctics) no presentaron diferenciación genética entre las muestras de C. undecimalis (FST=0.012). Sin embargo, los resultados de los análisis basados en clústeres bayesianos, componentes principales (PCA) y análisis discriminante de componentes principales (DAPC) sugieren la posible presencia de dos clústeres diferenciados genéticamente, pero sin ninguna relación con las áreas geográficas. Los resultados del análisis de cuello de botella poblacional no son significativos con valores de tamaño efectivo poblacional (Ne) elevados y similares entre los dos clústeres. Por el contrario, en E. marginatus, los análisis basados en microsatélites no muestran ningún patrón de subdivisión genética. El valor de FST es bajo y no significativo (FST=0.008), el análisis Bayesiano indicia un solo clúster y el PCA determina que todas las muestras de las diferentes localidades geográficas comparten la misma estructura genética. El análisis de cuello de botella muestra diferencias significativas con la observación de una baja Ne. Los resultados de los análisis genéticos en estas dos especies a lo largo de la costa sudeste de Brasil sugieren diferentes estructuras genéticas para cada especie y estos resultados deben tenerse en consideración para la estipulación de las medidas de conservación de la diversidad genética.

One of the major obstacles to propagating dusky grouper, Epinephelus marginatus, is the difficulty of rearing the early larvae. We have successfully raised dusky grouper larvae in mesocosms using a mixed diet of endogenous plankton grown in the rearing tank and an exogenous supply of Brachionus plicatilis and Artemia sp. Newly hatched larvae at an initial density of 1.3 ind.l-1 were stocked in partially shaded 3 m3 circular outdoor tanks during the summers of 2007 and 2008. Before introducing newly hatched larvae, the water was left for six days to promote plankton growth. Larval growth occurred at two different rates: i) a faster rate from first feeding to the beginning of metamorphosis, and ii) a slower rate at transformation. Survival at the beginning of metamorphosis was less than 10% (33 DPH) in 2007 and between 25 and 50% (25 DPH) in 2008. High mortalities were observed during larval transformation. The estimated minimum food requirement per grouper larvae increased more than 300% from the beginning of the notochord flexion to the beginning of metamorphosis. To meet such a high feeding requirement the number of larger prey organisms/copepods in the mesocosm should be eight times higher during this time period., Uno de los principales obstáculos para la propagación del mero, Epinephelus marginatus, ha sido la dificultad de la cría larvaria. Hemos conseguido la cría exitosa de larvas de mero en un mesocosmos utilizando una dieta mixta de plancton endógeno, desarrollado en el tanque de cría con suministro externo de Brachionus plicatilis y Artemia sp. Las larvas recién eclosionadas, con una densidad inicial de 1.3 ind.l-1 se colocaron en tanques circulares de 3 m3, al aire libre y parcialmente a la sombra, durante los veranos de 2007 y 2008. Antes de la introducción de las larvas recién eclosionadas, el agua se dejó durante seis días para promover el crecimiento del plancton. El crecimiento larvario se produjo a dos tasas distintas: i) más alta desde el inicio de la alimentación a la metamorfosis y ii) más baja durante la transformación. La supervivencia al inicio de la metamorfosis fue inferior al 10% (33 DPH) en 2007 y entre el 25 y el 50% (25 DPH) en 2008. Se observó una alta mortalidad de las larvas durante la transformación. La estimación del requerimiento alimenticio mínimo de las larvas de mero aumentó más del 300% desde el comienzo de la flexión de la notocorda hasta el inicio de la metamorfosis. Para satisfacer tan altos requerimientos alimenticios el número de grandes presas/copépodos en el mesocosmos debería ser de ocho veces durante este período de tiempo.

A pilot experiment of stock enhancement based on the release of hatchery-reared juveniles of dusky grouper, Epinephelus marginatus, was carried out at two artificial reefs located 0.9 km offshore the south-western Sicilian coast (Central Mediterranean). The fish assemblages inhabiting the reefs were characterized using underwater visual census (UVC) surveys. Despite some differences in fish species richness, diversity and abundance, both artificial reefs provide suitable feeding resources and shelter opportunities for the settlement of dusky grouper juveniles. A total of 95 dusky grouper juveniles, which were 3 and 4 years old, were released. No stress-related effects on fish swimming or behaviour were observed during the step by step transportation to the sea-bottom at 20 m depth. After release, several groupers showed very low reactivity; freezing and schooling were the most common behaviours. The sighting rate after one month of UVC surveys was 15.7% and 20% at the two artificial reefs. No effect of fish size at release on grouper survival was observed. Some groupers were not recorded on the pyramid of release but elsewhere in the same artificial reef, which demonstrated their ability to move around the reef. The extent of dispersal of the released juveniles largely exceeded the area encompassed by the reefs, which was shown by recaptures of tagged groupers by local fishermen up to 13 km from the release site. This result provides a first insight into the potential of stock enhancement of hatchery reared dusky grouper juveniles for marine ranching and conservation purposes., Un experimento de repoblación, basado en la liberación de juveniles de mero Epinephelus marginatus cultivados en criadero, fue realizado en dos arrecifes artificiales situados 0.9 kilómetros fuera de las costas sicilianas sur-occidentales (Mediterráneo Central). La ictiofauna de los arrecifes fue caracterizada a través de inmersiones submarinas, utilizando la técnica de censo visual (UVC). A pesar de algunas diferencias en número de especies, diversidad y abundancia, ambos arrecifes artificiales proporcionaron recursos alimenticios y refugio adecuados para el establecimiento de juveniles de mero. En total se liberaron 95 meros juveniles de 3 y 4 años de edad. Ningún efecto relacionado al estrés fue observado en el comportamiento de natación de los peces durante el gradual transporte hasta 20 m de profundidad. Después de la liberación, varios meros mostraron una reactividad muy baja, siendo el comportamiento más común quedarse inmóviles y agregados. Después de un mes de censos visuales, las tasas de avistamientos obtenidas en los arrecifes artificiales fueron de 15.7% y 20%. No se observó relación entre el tamaño en el momento de la liberación y la supervivencia. Algunos peces no fueron observados cerca del punto de liberación sino en otra parte del mismo arrecife artificial, demostrando así su capacidad de moverse por los alrededores. Según lo indicado por los pescadores locales que recobraron meros marcados hasta 13 kilómetros del punto de liberación, el grado de la dispersión de los juveniles liberados superó ampliamente el área abarcada por los arrecifes. Este resultado proporcionan la primera evaluación del potencial de los juveniles de E. marginatus cultivados en criadero para actividades de cría en mar y conservación.

The embryonic and early larval development of the laboratory-reared dusky grouper, Epinephelus marginatus (Lowe, 1834) are described and illustrated. The eggs, with a mean diameter of 846.68 ± 41 µm and a range from 736-940 µm, were spherical and transparent with transparent chorion. Embryonic development lasted 30 hours at 23°C. Newly-hatched larvae were 1.52 ± 0.066 mm in length. Absorption of the yolk sac was complete after the fourth day, when larvae reached 2.63 ± 0.123 mm in total length. The mouth opened 72 hours after hatching, and was in function after 96 hours, with an opening diameter ranging from 250-300 µm. Larvae had two fields of intensive pigmentation, one above the intestine, and the other between the anus and the end of the notochord.