Performance of raw material thermal treatment on formulated feeds for common octopus (Octopus vulgaris) ongrowing

• - Two diets based on dried raw materials and bogue (Boops boops) with different thermal treatment were successfully tested;
• - Application of temperatures below 60 °C in B. boops processing promoted better feeding rates than freeze-drying;
• B. boops (processed below 60°C) promoted similar growth, survival and proximate composition than freeze-dried bogue;
• -It is probable that thermal treatment, either than freeze-drying, affects nutritional content of raw materials for feeds.

The common octopus (Octopus vulgaris) has aroused great interest in recent years as a new species for aquaculture. However, the inexistence of feeds with an adequate and balanced nutritional profile for all life stages has hampered O. vulgaris aquaculture development. In the present study, O. vulgaris juveniles were fed with one of two different diets, based on dried raw materials (22% gelatine, 10% egg yolk, 10% Boops boops, 5% Todarodes sagittatus, 5% Carcinus mediterraneus, 2% fish oil, 3% glucose, 3% starch and 40% water) and differing only on bogue (B. boops) thermal processing (either freeze-dried — FDb or bogue meal prepared with temperature below 60 °C — Mb). Growth, feed efficiency, digestibility and condition were assessed after 56 days of rearing. Data were used to determine growth, weight gain (Wg), absolute growth rate (AGR), specific growth rate (SGR), absolute feeding rate, absolute protein feeding rate (APFR), absolute lipid feeding rate (ALFR), specific feeding rate (SFR), feed efficiency (FE), feed conversion ratio (FCR), protein productive value (PPV), lipid productive value (LPV), digestive gland index (DGI) and apparent digestibility coefficients (ADC). Both diets were accepted, promoted growth and faeces production with 100% of survival. No significant differences were found in growth (SGR of 0.78 ± 0.19%BW·day− 1 for FDb and 0.85 ± 0.09%BW·day− 1 for Mb), feed efficiency (48.31 ± 9.70% and 39.22 ± 2.92% for FDb and Mb, respectively), PPV and LPV. Despite the similarity on FCR (P > 0.05), a higher ingestion was found on Mb group regarding AFR (P < 0.01), APFR and ALFR (P < 0.01) and SFR (P < 0.05). In addition, the Mb octopi showed the highest DGI (6.75 ± 1.00%). Faeces proximate composition differed between groups in protein (P < 0.05), lipid (P < 0.05) and mineral content (P < 0.01) which were reflected in higher ADC for dry matter, protein and lipids in the Mb group (P < 0.01). Nonetheless, the proximate composition of tissues was similar between both groups (P > 0.05). The results revealed that dehydration of raw materials, performed under 60 °C (bogue-meal), had no effect on ingestion, digestibility, growth and survival when compared with the use of freeze-drying, which points out to the possible suitability of this thermal treatment for O. vulgaris feeds.