Energetic contribution of carbohydrates during starvation in common octopus (Octopus vulgaris)

Abstract

Our knowledge of the nutritional requirements of cephalopods is not very advanced and is limited by the poor availability of formulated diets that are both acceptable and nutritional (Cerezo Valverde et al., 2008). Most hypotheses on these requirements are based on the natural diets given to cephalopods and on biochemical analyses of these diets and the animals themselves (García García & Cerezo Valverde, 2006), on the intake of labelled nutrients (O'Dor et al., 1984) or on starvation experiments (Castro, Garrido & Sotelo, 1992). From such experiments it has been deduced that cephalopods are exclusively carnivorous and, contrary to what happens with proteins, that they rarely use carbohydrates (CH) or lipids as an energy source (Lee, 1994). However, it has been found that cephalopods do have the capacity to digest, store and use CH, which provides them with energy for anaerobic-burst work (Wells & Clarke, 1996). According to O'Dor et al. (1984) CH are rapidly catabolized after ingestion and only a small part accumulates as glycogen in the muscles, where it remains practically immovable during starvation. According to Hochachka & Fields (1982) glycogen may also be replenished rapidly directly from glucose in the circulation or from glycogenic amino acids. In contrast, variable but significant amounts of CH have been observed in all the tissues of many species of cephalopod, including the gonad (1–9% dry weight), digestive gland (3–13% dry weight) and muscle (1–8% dry weight), with respective values of 9%, 4% and 5% dry weight detected in Octopus vulgaris (Rosa, Pereira & Nunes, 2005a). Despite this, studies on the contribution of these substrates to metabolic energy in cephalopods are scarce compared with studies on proteins or lipids. The objective of this study was to analyse variations in the CH content of the digestive gland, gonad and muscle in O. vulgaris and their contribution to fuelling metabolism during starvation.