The digestive tract pH of the pygmy octopus (Paroctopus digueti) was evaluated. Octopuses were acclimated to captivity in fed and fasted treatments. The pH of all organs of the digestive tract was measured. Food intake (214.9 ± 157.6 mg) and transit time (8h) were evaluated. The pH of the digestive tract regions was acidic. No difference was found in the pH of fed and fasted octopuses.
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 pH of the internal part of the buccal mass (BMA), anterior salivary glands (ASG), posterior salivary glands (PSG), crop (CRO), stomach (STO), caecum (CAE), digestive gland (DGL) and intestine (INT) 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 hours, respectively. The apparent food transit time was approximately 8 h for the appearance of feces in the posterior intestine (Fig. 1) . The pH of the digestive tract regions was lower than pH 7.0. No difference was found when comparing fasting (6.41 ± 0.22) and feeding octopus (6.41 ± 0.23). DGL had the lowest pH (6.04 ± 0.12 in the wild and 5.97 ± 0.17 in feeding octopuses). The apparent transit of food over 8 h agrees with transit time in O. maya and O. mimus (Gallardo et al., 2017). The acidic pH of the digestive tract of P. digueti , is in agreement with the pH in O. maya (Vidal et al., 2014), O. bimaculatus (López-Peraza et al., 2014); and O. vulgaris (Sykes et al., 2020). Also, according to Linares et al. (2015), the pH in the DGL is the more acidic, although, in our study, we found values above pH 5.0 and not between pHs 3 and 4. All the above information is essential to understand the digestive physiology of the pygmy octopus. Attention must be paid to the fact that the physiological pH values of this species indicate the conditions of action of their digestive enzymes (fasting or feeding). In conclusion, the pygmy octopus has an acidic pH in its digestive tract in fasting and fed conditions.
References
Gallardo, P., et al. (2017). https://doi.org/10.3389/fphys.2017.00355.
Linares, M. et al. (2015). https://doi.org/10.3354/ab00642.
López-Peraza, D.J. et al. (2014). http://www.springerplus.com/content/3/1/22
Sykes, A.V. et al. (2020). https://doi.org/10.3389/fphys.2020.00765
Vidal, E.A.G. et al. (2014). Cephalopod culture: current status of main biological models and research priorities. ISBN: 978-0-12-800287-2