Effective use of glucose rather than starch in formulated semimoist diets of common octopus (Octopus vulgaris)

The aim of the present work was to test the capacity of Octopus vulgaris to use carbohydrates supplied in three diets: a diet without added carbohydrates (diet C0: 500 g kg−1 water, 200 g kg−1 gelatine, 100 g kg−1 egg yolk powder, 50 g kg−1 freeze‐dried Sardinella aurita and 150 g kg−1 freeze‐dried Todarodes sagittatus) and two obtained by substituting 50 g kg−1 of T. sagittatus by glucose (diet GLU50) or by starch (diet STA50). The most stable and best‐accepted diet was STA50 (SFR 1.26%BW day−1) although there were no significant differences in the growth rates obtained with the three diets: 10.12 g day−1, 9.37 g day−1 and 11.22 g day−1 for C0, GLU50 and STA50, respectively (P > 0.05). The feed efficiency indices were better for GLU50, of particular note being the protein productive value of 71.88% and a feed conversion ratio lower than 1. Protein and lipid digestibility were similar in all the three diets (96–98% for proteins and 85–94% for lipids), whereas carbohydrate digestibility was higher in GLU50 (98%) than in C0 (84%) and STA50 (0.33%). The content of carbohydrates increased in muscle and the digestive gland as a consequence of the increased carbohydrates intake.