pH evaluation in the digestive tract of the pygmy octopus, Paractopus digueti

This study is considered the first report on the digestive tract pH of the pygmy octopus (Paroctopus digueti). Adult octopuses obtained from the wild (mean ± SD) (42.1 ± 15.1 g), and those acclimated to captivity in a fed (25.4 ± 9.0 g, n = 15) or fasted (23.1 ± 6.1 g, n = 15) state, were studied. The digestive tract regions of buccal mass (BMA), anterior salivary glands (ASG), posterior salivary glands (PSG), crop (CRO), stomach (STO), caecum (CAE), digestive gland (DGL) and intestine (INT) were dissected. The pH of the internal part of the digestive tract regions was measured. Food intake (dry weight) per octopus was 53.8 ± 35.1 mg to 214.9 ± 157.6 mg at 15 min and 8 h, respectively. The apparent food transit time was approximately 8 h for the appearance of feces in the posterior intestine. In all cases, the pH of the digestive tract regions was lower than pH 7.0. No statistical difference was found when comparing the pH by digestive tract regions between wild octopuses and octopuses in captivity (fasting and feeding). In acclimatized octopuses, the average pH was 6.41 ± 0.22 and 6.41 ± 0.23 for fasting and fed octopuses, respectively. Although DGL had the lowest pH values relative to other digestive tract tissues (p < 0.05), pH was always >5.0 (6.04 ± 0.12 in the wild and 5.97 ± 0.17 in feeding octopuses). In conclusion, the pygmy octopus has an acidic pH in its digestive tract under fasting and feeding conditions.