Morphological and functional development of the spiral intestine in cloudy catshark (Scyliorhinus torazame)

Abstract

Cartilaginous fish have a comparatively short intestine known as the spiral intestine that is comprised of a helical spiral of intestinal mucosa. However, morphological and functional development of the spiral intestine is not well described. Unlike teleosts, cartilaginous fish are characterized by an extremely long developmental period in ovo or in utero for example; in the oviparous cloudy catshark (Schyliorhinus torazame), the developing fish remains inside the egg capsule for up to six months, suggesting that the embryonic intestine may become functional prior to hatch. In the present study, we describe the morphological and functional development of the spiral intestine in the developing catshark embryo. Spiral formation of embryonic intestine was completed at the middle of stage 31, prior to “pre-hatching”, which is a developmental event characterized by the opening of egg case occurring at the end of the first third of development. Within 48 hours after pre-hatching event, egg yolk began to flow from the external yolk sac into the embryonic intestine via the yolk stalk. At the same time, there was a rapid increase in mRNA expression of the peptide transporter pept1 and neutral amino acid transporter slc6a19. Secondary folds in the intestinal mucosa and microvilli on the apical membrane appeared after pre-hatching, further supporting the onset of nutrient absorption in the developing intestine at this time. We demonstrate the acquisition of intestinal nutrient absorption at the pre-hatching stage of an oviparous elasmobranch.