Cephalopods are important model organisms for neuroscience, physiology and ethology research. For that reason, the initial trials of cephalopod’s maintenance were mainly to provide live specimens for research or aquariums (Boletzky and Hanlon, 1983). However, the importance of cephalopods for human consumption was rising. Consequently, their commercial importance has also risen substantially in recent decades. It is obvious to expect the increasing cephalopod harvest in order to satisfy the growing demand. Nonetheless, we must not forget that cephalopods are also valuable as forage for commercial fishes and therefore, a trade-off between the commercial and ecological value must be encouraged (Hunsicker et al., 2010). In this context, aquaculture offers a reduction of fishing pressure on wild cephalopod stocks and a constant supply of the product to the market. This is particularly important in countries like Spain, Italy and Japan, which are the largest consumers and importers of cephalopods (FAO, 2012). Particularly in Spain, the fishing sector demanded the diversification of the marine farming industry, based on mussels (Mytilus
bream (Sparus aurata) (Chapela et al., 2006; Vaz-Pirez et al., 2004). Thus, farming trials were developed using O. vulgaris as a new species target due to their high value in the market, short life cycle (12-18 months), high fecundity (100, 000- 500,000 eggs per female), high food conversion rates (assimilating 40-60% of ingested food), its rapid and easy adaptation to captivity conditions and acceptance of frozen food (Iglesias et al., 2000; Vaz-Pirez et al., 2004). To date, the octopus aquaculture is established as a successful activity that in 2011 produced 2,755 kg equivalent to 19,330€ (Anuario de Acuicultura, 2011). However, the first trial to evaluate the viability of this culture in laboratory conditions started during 1995-1999 (Iglesias et al., 2000). The results demonstrated the feasibility of fattening octopuses mainly with crustaceans (80% of the diet). Individuals weighing 300 g achieved 2,200 g in weight in 4 months, whereas octopuses weighing 1,300 g reached 12,300 g after 10 months of fattening (Iglesias et al., 2000). Parallel fattening research was conducted in floating cages in the Ria of Muros (Galicia). After feeding octopuses with fishes of low economic value, similar results in octopus growth rates (0.3-0.8 kg/month) were obtained (Rama-Villar et al., 1997). The potential of O. vulgaris culture was thus evident and promoted the establishment of five companies for intensive on-growing. Octopuses of 750 g (minimum legal weight in 1995) were reared in cylindrical or square shaped cages (Fig. 3), providing individual dens with a total capacity of 150 octopuses. The fattening program lasted 4 months and three fattening cycles were initially conducted during the year (Iglesias et al., 2000). However, wide variation in weight and profitability were obtained. The economic analysis of this activity revealed that supply of juveniles produced in laboratory and availability of artificial diets (for paralarvae and sub-adults) are needed to reduce costs and make it a profitability activity (García-García et al., 2004). Nevertheless, to complete the octopus life cycle in captivity is still a challenge.
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Fig. 3. Culture system (A) cylindrical and (B) square shaped cages used for rearing O. vulgaris in Galicia (From: Iglesias et al., 2000).
The main constraint to complete commercial rearing of the common octopus is the high paralarvae mortality during the first weeks of life (Iglesias et al., 1997). The hatchling cephalopods are planktonic and carnivorous, and require live prey of suitable size with high protein content and swimming behavior (Villanueva, 1994). Successful rearing experiments of the common octopus from paralarvae to juveniles have been developed using zoeae of crustaceans like Liocarcinus depurator and Pagurus prideaux, reaching a survival rate of 34.6% as individuals reached 30 days old (Villanueva, 1994; 1995). An Artemia based diet complemented with zoeae of Maja squinado has also been used, but only 0.2% of juveniles (individuals of 52 days) reached survival (Moxica et al., 2002). Iglesias et al. (2004) used the same mixed diet Artemia–M. squinado and reared paralarvae of up to 8 months old. However, from an economic point of view, the use of zoeae is not suitable for large-scale cultivation. Hence, additional prey to be reared commercially or artificial diets are required (Fuentes et al., 2011). To complete such goal, the paralarval feeding needs should be elucidate (Iglesias et al., 2006). To date, molecular detection of prey in wild paralarvae’s stomach has contributed to reveal the range of prey that paralarvae typically consume in the sea (Roura et al., 2010). Meanwhile, biochemical studies have pointed out that a deficiency of polyunsaturated fatty acids in prey like Artemia, also poor in protein content, is the cause of low growth and low survival in captivity (Navarro and Villanueva, 2000; Iglesias et al., 2007). Co-feeding techniques tried in paralarvae included a combination of life prey Artemia and microcapsules
with 84-91% moisture. However, low or no growth in paralarvae was obtained when compared to the single Artemia diet (Villanueva et al., 2002). Fuentes et al. (2011) demonstrated that Artemia enriched with the microalgae Nannochloropsis sp. produces a higher paralarvae growth, in average, 1.61 mg and 46% of survival at day 30, than feeding individuals with Artemia enriched with sand eel (Hyperoplus lanceolatus) or crushed wild zooplankton. Nonetheless, results reported to date do not surpass the mean weigh value of 17.4 mg reported on paralarvae at 60 days (benthic phase) by Villanueva (1995). Presumably, the minimum nutritional requirements are covered in the planktonic phase but have not yet been established for the planktonic settlement phase. However, additional nutritional factors implicated in growth and survival are needed and therefore, further research is yet to be done (Fuentes et al., 2011).
The rearing of octopus in suspended cages in the sea depends on the supply of sub- adults captured by fishermen, but also on the availability of formulated diets that will support the commercial production of the species and will make the octopus culture a profitably activity (Lee, 1994; García-García et al., 2004; García-García and Cerezo-Valverde, 2006; Cerezo-Valverde et al., 2008). The octopus diet in the wild is mostly composed by crustaceans, but also by fishes and molluscs (Guerra et al., 1978). Crabs have provided better results than fish or molluscs in octopus growth (Cagnetta and Sublimi 2000). However, because crab supply could be expensive, discarded or low market value fish, such as Boops boops, Sardina
pilchardus, Sardinella aurita or Trachurus mediterraneus),are usually used to feed octopus
(Socorro et al., 2005; García-García and Aguado-Giménez, 2002; Rodríguez et al., 2006). To date, the economic viability of the octopus culture is still in progress and will be certainly achieved once the full biological cycle can be reproduced under controlled conditions, and the formulated diets and the necessary technology for a rearing system have been developed (García-García et al., 2004).
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