Growth of common octopus (<em>Octopus vulgaris</em>) in cages suspended from rafts

Abstract

SUMMARY: Two ongrowing experiments were conducted using a raft deployed for rearing mussels during summer and winter in the Ria of Vigo, Galicia, NW Spain. Two 3 m x 1.5 m x 6 m galvanized iron ongrowing cages were suspended from this platform, each equipped with dens constructed from PVC pipe. Small common octopus (Octopus vulgaris) were captured by the small-scale creel fishery in the ria and placed in one of two sex-specific experimental cages. Specimens were fed a standard diet (fish, decapod crustacean and mussels) at a daily feeding rate of 5% of the total weight of the animals in each cage. Due to the very high mortality as a result of decreased salinity in the winter experiment and spawning during the summer experiment, only data from the first 75 days of each experiment were compared. Growth rates were significantly higher in summer than in winter for both sexes, which was probably due to higher ambient culture temperatures during summer. Mortality was also higher during summer than winter. It was concluded that culture of common octopus on mussel rafts may be viable, especially if problems related to salinity, the acquisition of specimens from the wild and losses due to spawning can be reduced.Keywords: Octopus vulgaris, growth, ongrowing, NW Spain. RESUMEN: CRECIMIENTO DE PULPO COMÚN (OCTOPUS VULGARIS) EN JAULAS FLOTANTES. -En este estudio se realizaron dos experimentos de engorde de pulpo común (Octopus vulgaris) en jaulas suspendidas desde una plataforma de cultivo de mejillón en la Ría de Vigo (Galicia, noroeste de España). Las dimensiones de cada jaula de hierro galvanizado fueron 3 x 1,5 x 6 m, y cada una de ellas estaba equipada con cobijos de PVC. Los pulpos de pequeño tamaño se obtuvieron en la pesquería de la Ría de Vigo y se introdujeron por separado, machos y hembras, en cada una de ellas. Los ejemplares fueron alimentados con una tasa de alimento del 5% del peso medio de los animales de cada jaula con una dieta estándar compuesta por peces, crustáceos decá-podos y mejillón. Únicamente se utilizaron los datos de los 75 primeros días de cada experimento debido a la elevada mortalidad de los animales al final del experimento de inverno por descenso brusco de la salinidad y al desove de los animales de verano. Las tasas de crecimiento de ambos sexos fueron significativamente más altas en verano que en invierno posiblemente debido a las mayores temperaturas ambientales durante el estío. La mortalidad fue más elevada en verano que en invierno. Esta experiencia indicó que el engorde de pulpo en jaulas sería viable, especialmente si los problemas debidos al descenso de la salinidad, la obtención de ejemplares de la naturaleza y al desove de las hembras pueden reducirse.

Effects of three culture densities on growth and survival of Octopus vulgaris (Cuvier, 1797)

“…Growth rates, close to 1% %BW/day, were similar to the ones reported for this species at Sublimi 1999, 2000;García García and Aguado 2002) and were higher than those reported by Otero et al (1999), Iglesias et al (1999Iglesias et al ( , 2000 and Chapela et al (2006), who cultured this species at lower temperatures. Temperature greatly influences cephalopod growth , food conversions (Domingues 1999) and ingestion (Domingues et al 2006(Domingues et al , 2007.…”

“…Octopuses were fed frozen squid (Loligo gahi) once a day at 14:00 h, at 5% body weight per day (%BW/day). The rations should be appropriate for on-growing of this species, based on previous studies by Aguado and García García (2002), García García and Aguado (2002), and Chapela et al (2006). Food remains were collected from the tanks on the next morning and weighed previous to feeding.…”

Growth of <i>Octopus vulgaris</i> (Cuvier, 1797) in tanks in the Ebro Delta (NE Spain): effects of temperature, salinity and culture density

“…Mangold (1983) reported a salinity range of 32-44 in the areas where the species is known to occur. Studies carried out in cages suspended from rafts in the Ria of Vigo, NW Spain, (Chapela et al, 2006) reported high mortalities in winter, when the salinity dropped below 29, which is below the limit of tolerance described for this species by Mangold (1983). Sobrino et al (2002) reported that heavy rainfalls caused landings of O. vulgaris to drop.…”

“…Numerous studies have analyzed physiological and nutritional aspects of octopus ongrowing in tanks, but all of them used one individual per tank García and Cerezo, 2006). Other studies have evaluated factors such as stocking density using cages suspended from rafts (Chapela et al, 2006) or floating cages (Rodríguez et al, 2006).…”

“…Many ongrowing studies using floating cages or tanks have been carried out along the Spanish coast Iglesias et al, 2004;Chapela et al, 2006) but, to date, few ongrowing experiments in tanks on an industrial scale have been done. The octopus is inherently a territorial species and requires a minimum space for its development and growth.…”