3D Reconstruction of the Digestive System in Octopus vulgaris Cuvier, 1797 Embryos and Paralarvae during the First Month of Life.

Raquel Fernández-Gago,Martin Heß,Francisco Rocha,Heidemarie Gensler

doi:10.3389/fphys.2017.00462

Raquel Fernández-Gago, Martin Heß + Show 2 more

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https://doi.org/10.3389/fphys.2017.00462

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Abstract

Octopus vulgaris aquaculture is limited due to poor biological knowledge of the paralarval stages (e.g., digestive system functionality), their nutritional requirements (e.g., adequate live diet) and standardization of rearing techniques. These factors are important in explaining the high mortality rate observed in this developmental stage under culture conditions. For a better understanding of nutrition biology of this species, we investigated the 3D microanatomy of the digestive tract of the embryo and paralarvae during the first month of life. O. vulgaris paralarvae digestive system is similar to that in the adult. The “descending branch” has a dorsal position and is formed by the buccal mass, oesophagus and crop. Ventrally, the “ascending branch” is formed by the intestine and the anus. The digestive gland, the posterior salivary glands and the inner yolk sac (in the case of the embryo and hatched paralarvae) are located between the “ascending” and “descending” branches. In the curve of the U-shaped digestive tract, a caecum and the stomach can be found. The reconstructions reveal that anatomically the digestive system is already complete when the paralarvae hatch. The reconstruction of the buccal mass at different post-hatching days has demonstrated that all the necessary structures for food intake are present. However, the radula surface in contact with the pharynx is very small on the first day of life. Although the digestive system has all the structures to feed, the digestive gland and radula take longer to reach full functionality. We have established four development periods: embryonic, early post-hatching, late post-hatching and juvenile-adult. The differentiation between these periods was done by type of feeding (endogenous or exogenous), the state of maturation and hence functionality of the digestive gland, type of growth (linear, no net, or exponential), and measurement of the arm lengths with respect to the mantle length. 3D reconstruction represents a new tool to study the morphology and functionality of the cephalopod digestive system during the first days of life.

Highlights

Octopus vulgaris aquaculture is limited due to a number of factors including: poor physiological and biological knowledge of the paralarval stages, their nutritional requirements, a live diet with adequate composition, and the standardization of rearing techniques (Moxica et al, 2002; Iglesias et al, 2007; Iglesias and Fuentes, 2014)
The total length (Table 1) at the fifth post-hatching day was 2.99 ± 0.23 mm, the dorsal mantle length was 2.08 ± 0.15 mm and the arms present a mean length of 0.625 ± 0.066 mm with 3 suckers
Octopus vulgaris completes embryonic development as a planktonic stage called paralarva (Young and Harman, 1988). During this post-hatching stage, the transition between endogenous and the exogenous feeding occurs, which is considered as a critical period characterized by high mortality (Iglesias and Fuentes, 2014)

Summary

Introduction

Octopus vulgaris aquaculture is limited due to a number of factors including: poor physiological and biological knowledge of the paralarval stages, their nutritional requirements, a live diet with adequate composition, and the standardization of rearing techniques (Moxica et al, 2002; Iglesias et al, 2007; Iglesias and Fuentes, 2014). Major changes in shape and morphology of the organs occur in the larval stage of development In teleost ontogeny, these changes in the alimentary tract occur in both morphology and function (Dabrowsky, 1986). These changes in the alimentary tract occur in both morphology and function (Dabrowsky, 1986) This can be observed using methods that detect both, morphological and functional changes. Comparative studies of digestive system development have been performed in a number of fish species including Solea solea (Boulhic and Gabaudan, 1992), Dicentrarchus labrax (Beccaria et al, 1991), Dentex dentex (Crespo et al, 1992), Pagrus pagrus, and Diplodus sargus (Darias, 2005)

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