The Digestive Tract of Cephalopods: Toward Non-invasive In vivo Monitoring of Its Physiology

Abstract

Ensuring the health and welfare of animals in research is paramount, and the normal functioning of the digestive tract is essential for both. Here we critically assess non- or minimally-invasive techniques which may be used to assess a cephalopod's digestive tract functionality to inform health monitoring. We focus on: (i) predatory response as an indication of appetitive drive; (ii) body weight assessment and interpretation of deviations (e.g., digestive gland weight loss is disproportionate to body weight loss in starvation); (iii) oro-anal transit time requiring novel, standardized techniques to facilitate comparative studies of species and diets; (iv) defecation frequency and analysis of fecal color (diet dependent) and composition (parasites, biomarkers, and cytology); (v) digestive tract endoscopy, but passage of the esophagus through the brain is a technical challenge; (vi) high resolution ultrasound that offers the possibility of imaging the morphology of the digestive tract (e.g., food distribution, indigestible residues, obstruction) and recording contractile activity; (vii) needle biopsy (with ultrasound guidance) as a technique for investigating digestive gland biochemistry and pathology without the death of the animal. These techniques will inform the development of physiologically based assessments of health and the impact of experimental procedures. Although intended for use in the laboratory they are equally applicable to cephalopods in public display and aquaculture.

The Current State of Cephalopod Science and Perspectives on the Most Critical Challenges Ahead From Three Early-Career Researchers

“…For instance, ultrasonography is considered to be a suitable tool to determine sex and the maturation status of the gonads, and to assess the body condition of living animals. In O. vulgaris , ultrasonography has also been used to observe mantle contractions during locomotion and respiration ( Tateno, 1993 ), the central nervous system ( Grimaldi et al, 2007 ), the arms ( Margheri et al, 2011 ) and the digestive tract ( Ponte et al, 2017 ). In S. officinalis , ultrasound has been used to analyze cardiovascular activity ( King et al, 2005 ), as well as cardiac and ventilatory rates in response to sudden visual stimuli ( King and Adamo, 2006 ).…”

“…In addition to ultrasound, other non- or minimally invasive methods have recently begun to be explored. For instance, a series of techniques, including behavioral responses to prey, the rate of food intake, fluctuations in body weight, oro-anal transit times, defecation frequencies, fecal appearance and composition, endoscopic assays, and needle biopsy (which may require ultrasound guidance) have been suggested as methods to assess the digestive health of cephalopods ( Ponte et al, 2017 ). Another group of researchers have recently tested methods for in vivo sex determination of adult cuttlefish ( S. officinalis ) using an endoscope ( Sykes et al, 2017b ).…”

Anatomical and histochemical features of the digestive system ofOctopus vulgarisCuvier, 1797 with a special focus on secretory cells

“…Because of their ecological importance and biological characteristics, cephalopods have been included in the European Union Legislation (Directive 2010/63/EU) regulating the use of animals for scientific purposes. This directive has prompted studies on the care and welfare of cephalopods in the laboratory (Fiorito et al., ; Ponte, Sykes, Cooke, Almansa, & Andrews, ; Sykes, Almansa, Cooke, Ponte, & Andrews, ) and with the aim of improving culture of cephalopods, their living conditions and the manner in which experimental procedures are carried out (Fiorito et al., ). Octopus vulgaris is a cephalopod species with of high commercial value worldwide, with 34 thousand tonnes landed in 2015 (FAO ).…”

Can Cephalopods Vomit? Hypothesis Based on a Review of Circumstantial Evidence and Preliminary Experimental Observations

“…Quantifying the ability of cephalopod digestive tract secretions with a pH 5–6 to degrade small fish bones, scales, and fragments of crustacean exoskeletons at body temperature will provide part of the answer to their fate in the digestive tract. However, detailed studies of the composition of feces (as proposed by Ponte et al, 2017) are also required to enable a more informed conclusion to be reached about voiding by defecation vs. the possibility that indigestible residues are voided by vomiting or regurgitation.…”