Multidisciplinary approach to the culture of common octopus (octopus vulgaris) paralarvae. Feeding, nutrition and stress biomarkers

Laburpena

The common octopus (Octopus vulgaris, Cuvier 1797) is a promising species for aquaculture diversification, but the massive mortality during the first life stage is the main bottleneck for its commercial production. In order to progress in its culture it is necessary to address some aspects which remain unstudied such as: (i) Statistically assessing the huge variability in the methodology and results obtained from the different studies carried out till date; (ii) Testing, by using wild paralarvae as reference, if the changes observed in the composition of reared paralarvae are due to its own development or to the rearing conditions; (iii) Evaluating paralarvae stress response by analysing if they can be affected by the diet and/or origin of populations. The present thesis aimed at improving growth and survival of common octopus paralarvae through a multidisciplinary approach taking into account aspects such as feeding, nutrition and stress in order to deal with the issues exposed above. To tackle the first purpose, the effect of feeding with different live preys and Artemia enrichments methods in paralarval growth was compared using a meta‐analysis approach. A total of 26 independent assays were used, including data from the bibliography and from experiments carried out by our group. Regardless the high variability in zoo‐technical and nutritional conditions among studies, meta‐analysis results pointed out that paralarvae fed with crustacean zoeae showed an improvement on growth (dry weight) versus to paralarvae fed with Artemia. However not all crustacean species displayed the same results, given that results with Grapsus zoeae were highly variable, hampering to find significant differences with respect to the control treatment (Artemia). With respect to Artemia enrichments, marine lecithin LC60®, rich in docosahexaenoic acid (DHA, 22:6n‐3) and polar lipids (PL) displayed a beneficial effect on paralarvae growth, possibly associated to the essential role of these lipid compounds in early stages of development. To address the second issue, the fatty acid profile of wild paralarvae of known age was individually characterised to confirm if changes observed in the composition of reared individuals also happen in the wild. Age was estimated for the very first time on wild paralarvae through daily deposition increments on the lateral hood surface of the beaks. In addition, the lipid analysis of individual paralarvae allowed assessing sample population variability and comparing them with reared paralarvae. This study found significant differences in the fatty acid composition between wild and reared paralarvae, being DHA the most striking variation with lower levels in reared paralarvae. Finally, we evaluated O. vulgaris paralarvae stress status by analysing biomarkers of stress and nutritional condition and how they could be affected by the diet and/or origin of populations. The results revealed that both initial dry weight and biomarkers in hatchlings were related with the geographical origin of the broodstock. Likewise, 15 days old paralarvae presented significant differences in specific growth rate (SGR) and biomarkers associated with both geographical origin and dietary regime. Paralarvae fed with LC60 showed a higher SGR as well as an increase in antioxidant defences, possibly as a result of high contents in highly polyunsaturated fatty acids (HUFA).