Growth and digestibility of formulated diets based on dry and freeze-dried ingredients in the common octopus (Octopus vulgaris)

Abstract

We studied the growth of O. vulgaris and the digestibility of two semi-moist diets (50% water) based exclusively on dry and freeze-dried ingredients (Diet S: 20% gelatin, 10% egg yolk powder, 5% Sardinella aurita and 15% Todarodes sagittatus; and Diet P: the same as the previous diet but substituting T. sagittatus by pea). Both diets had a similar macronutrient composition (70–73% protein DW, 12–13% lipids DW), a firm texture when introduced into the water and good acceptability. Survival was 100% with both diets. The specific feeding rates were also similar for both diets (1.0% body weight/day; P>0.05), although the best results were obtained with diet S, which was responsible for an absolute growth rate of 9.6g/day and a feed conversion rate of 1.0, compared with the 2.2g/day and 3.9 obtained with diet P; P<0.05). The protein and lipid productive values were significantly higher for diet S than for diet P (43.6 and 13.3% vs. 20.2 and −0.5%, respectively). The good results obtained with diet S may be explained by its greater digestibility (93.3% for dry matter, 97.0% for proteins and 87.9% for lipids) compared with the corresponding value for diet P (73.8%, 92.1% and 85.0%, respectively). The findings demonstrate that O. vulgaris can be fed with dry or freeze-dried ingredients that have undergone mild heat treatments since they lead to good growth, feed efficiency and digestibility. Future studies on octopus on-growing could use a similar base to that proposed in this paper to obtain diets with better acceptability, stability or nutritional composition for commercial purposes.