Digestive enzymes and timing of digestion in Octopus vulgaris type II

Abstract

The study of digestive physiology is a crucial aspect enabling commercial aquaculture of Octopus vulgaris type II. Knowing the processes of digestion, absorption, and assimilation of nutrients and factors that modulate the digestive environment is fundamental for designing adequate diets based on the digestive capacity of the animals. In the present study, we characterized the activity of total proteases in the gastric juice and digestive gland in adult O. vulgaris type II both fasted and during the postprandial period, and evaluated their digestive dynamics. In vitro experiments showed this species had predominantly acidic digestion, with maximal proteolytic activity at pH 3–4 and temperatures of 50 °C and 70 °C. These results confirmed the carnivorous feeding habit and high adaptive capacity of digestive enzymes in this species. The digestion time was 400 min at 20 °C when the digestive tract was ready to receive its next meal. Digestion occurred in two stages: the first, at the beginning of digestion, with rapid passage of soluble nutrients along the digestive tract; the second, which was slower, and involved the digestion, absorption, and assimilation of more complex nutrients (proteins and lipids). The ingestion peak occurred at 200 min after feeding when proteolytic activity was maximal. This species uses proteins as its primary source of energy and mobilizes proteins before lipids during intracellular digestion, which is a different digestion pattern to other tropical and subtropical-temperate octopus species. This new information contributes to a better understanding of the digestive physiology of O. vulgaris type II and is essential for formulating specific commercial diets for its farming.