Due to the high mortality rates and poor growth generally observed in Octopus vulgaris paralarval rearing experiments, it was decided to organize a working group in order to formulate recommendations to tackle this problem. Over a dozen scientists representing the most active current research groups related to this subject attended the meeting in Vigo, Spain, in November 2005. The aim of this working group was to determine the bottlenecks that prevent success in paralarval rearing, define the most appropriate rearing conditions, and identify required future research. This paper describes rearing techniques for the O. vulgaris paralarvae used by the different research participant teams, with regard to tank systems, feeding environment, and diets (Artemia, crustacean zoeae, sandeel flakes, copepods, etc.). Additionally, it includes other related themes such as the culture of Artemia and copepods, organisms that are commonly used in paralarval rearing. When embarking on O. vulgaris rearing it is advised to use prey rich in DHA (docosaenoic acid, 22:6n-3) and EPA (eicosapentaenoic acid, 20:5n-3), and with high DHA/EPA ratio. Such prey could be enriched Artemia, accompanied or not by crustacean zoeae or any microdiet. It is also recommended that, in future studies, values of growth and survival rates are recorded at the beginning of the benthic phase, in order to compare them to successful previous studies. Dry weight and DHA/EPA ratio of paralarvae may also be good criteria to define paralarval viability and evaluate success of the rearing system.

The aim of this study was to evaluate growth, biochemical composition and dietary nutrients utilization in Octopus vulgaris fed on four diets based on bogue Boops boops, from different origin and in two presentations: fresh discarded bogue (aquaculture by‐product) (DB‐f), fresh wild bogue (low price trash species) (WB‐f), discarded bogue agglutinated moist diet (DB‐m) and wild bogue agglutinated moist diet (WB‐m). Diets based on DB showed higher lipid content (19–26% dw) than those based on WB (5–6% dw). Octopuses fed on DB‐based diets showed higher growth (1.5–1.9% day−1) and higher protein efficiency ratio (0.64–0.69) than those fed on WB‐based diet (1.1–1.5% day−1 and 0.36–0.37 respectively), which suggests good utilization of dietary lipids and also a possible protein sparing effect by lipids in O. vulgaris. Octopuses fed on diets presented fresh showed a higher growth (1.9–1.5% day−1) and a higher feed efficiency (62–65%) than those fed on agglutinated diets (1.1–1.5% and 52–60% day−1 respectively). Regarding fatty acids, the digestive gland clearly reflected dietary lipid and fatty acid profile, while muscle showed a more stable composition. Low dietary ARA content reflected in octopus tissues, especially in specimens fed on DB‐based diets, which did not seem to affect growth during the experimental period.

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The objective of the present study was to investigate the combined effect of several dietary contents of vitamin E and polyunsaturated fatty acids (PUFA), mainly docosahexaenoic acid (DHA), on growth, survival, biochemical composition and tissue morphology of sea bass along early development. A feeding experiment was conducted in sea bass larvae using five different diets with the same proximate composition and different ratios of DHA concentrated fish oil [10, 30 and 50 g kg−1 dry weight (DW)] and vitamin E (α‐tocopherol acetate) (1500 and 3000 mg kg−1 DW). DHA was readily deposited in fish tissues and associated with higher sea bass mortalities probably because of increased peroxidation risks. Besides, the elevation of dietary DHA contents up to 5% severely increased the incidence of muscular lesions and the presence of ceroid pigment within hepatocytes. However, elevation of dietary vitamin E levels markedly reduced the incidence of these symptoms in sea bass, increasing the tissue content in several PUFA and improving growth and stress resistance. Moreover, when sea bass was fed diets containing high vitamin E levels, fish showed a significant improvement in growth when dietary DHA was raised from 1% to 3%. Therefore, in sea bass larvae, a ratio of 30 g kg−1 DHA and 3000 mg kg−1 vitamin E seems to be adequate to achieve a good larval performance and to avoid muscular lesions.

DHA deficiency has been related to skeletal malformations in fish, but high DHA levels have produced controversial results that could relate to the oxidative status of fish tissues in the different reports. In the present study, gilthead seabream (Sparus aurata) larvae were fed deficient, adequate or high DHA levels, or high DHA levels supplemented with the antioxidant a-tocopherol. Larvae fed deficient DHA levels tended to be smaller, and showed the highest incidence of urinary bladder calculi, lordosis and kyphosis and the lowest number of mineralised vertebrae for any given size class. Elevation of dietary DHA increased larval growth and significantly enhanced the expression of the insulin-like growth factor 1 (IGF-1) gene. However, a DHA level increase up to 5 % raised the degree of lipid oxidation in larval tissues and deformities in cranial endochondral bones and in axial skeletal haemal and neural arches. The increase in dietary a-tocopherol supplementation in high-DHA feeds reduced again the occurrence of skeletal deformities. Moreover, the expression of genes coding for specific antioxidants such as catalase, superoxide dismutase or glutathione peroxidase, which neutralised reactive oxygen substances formed by increased dietary DHA, was significantly decreased in larvae fed high a-tocopherol levels. These results denoted the importance of DHA for early bone formation and mineralisation. Low dietary DHA levels delay early mineralisation and increase the risk of cranial and axial skeletal deformities. Excessive DHA levels, without an adequate balance of antioxidant nutrients, increase the production of free radicals damaging cartilaginous structures before bone formation.