Characterization of the digestive tract of wild ayu

Abstract

The gut and gut contents of ayu Plecoglossus altivelis caught in the Ohta River in Hiroshima prefecture, Japan were examined. Relative intestine length (intestine length/body length) was almost constant. Except for relative intestine length, characteristics of the gut of wild ayu were not significantly different from those of cultured ayu. The height of intestinal folds increased and their width declined from stomach to anus. Cyanobacteria (Homoeathrix sp. and Calothrix sp.) and diatoms (Cymbella sp., Gomphonema sp., Melosira sp., Navicula sp., and Synedra sp.) were well digested during passage through the gut despite a lack of apparent destruction. In contrast, green algae (Dictyosphearium sp., Coelastrum sp., and Pediastrum sp.) exhibited little degradation. The pH of stomach contents ranged from 2.8 to 7.4 (mean ± SD = 4.1 ± 1.0), whereas that of the posterior intestine was 7.0–8.5 (7.9 ± 0.4). Gut contents of wild ayu increased with bodyweight, and were more than threefold greater than those of cultured ayu, suggesting that wild ayu compensate for low nutrient content of algae through the continuous ingestion of large quantities of feed organisms.

Ontogeny of the gastrointestinal tract and selected digestive enzymes in cobia Rachycentron canadum (L.)

“…As far as is known, the pyloric caecae of cobia juveniles and adults has not been described and although a detailed description is beyond the scope of this study a few general observations were made regarding this structure. In juvenile fish, the gross morphology of the pyloric caecae resembled that described for Ayu Plecoglossus altivelis (Temminck & Schlegel) (Nakagawa et al, 2002) in which several 'stalks' emanated from the proximal end of the AI each branching multiple times to form numerous blind sacs. The number of caecae increased as cobia increased in size and appeared to number in the thousands in adult fish.…”

Why be amphidromous: expatrial dispersal and the place of source and sink population dynamics?

“…The trophic habits of most sicydiine gobies are undescribed, but where known, these fishes often rapidly become herbivores when they settle in fresh waters (Schoenfuss et al 1997;Fitzsimons et al 2003), and they feed by grazing periphyton from the stream substrate. In so doing, they avoid the problem of finding enough small-sized animal foods-herbivory is especially well known in some of the speciose sicydiine gobies, and is also true of the Japanese ayu (Plecoglossus-f. Osmeridae; Nakagawa et al 2002;Abe et al 2007) and the Australian and New Zealand so-called graylings (genus Prototroctes-f. Prototroctidae; McDowall 1976McDowall , 1990, all of which are amphidromous.…”

Morphology of the digestive tract of the Whitemouth croaker Micropogonias furnieri (Desmarest, 1823) (Perciformes: Sciaenidae)

“…Alves and Tom e (1966) observed in Scomberomorus cavalla that pyloric caeca show different levels of development, which was also observed in M. furnieri, whose caecum showed projections of different sizes and thickness. Nakagawa et al (2002) reported larger number of caeca with the ontogenetic development of the herbivore Plecoglossus altivelis. Pyloric caeca are histologically similar to the intestines, presenting villi that increase the surface available for absorption and secretion, but also work as a food reservoirs.…”

“…Nakagawa et al . () reported larger number of caeca with the ontogenetic development of the herbivore Plecoglossus altivelis . Pyloric caeca are histologically similar to the intestines, presenting villi that increase the surface available for absorption and secretion, but also work as a food reservoirs.…”