Morphological structure and allometric growth pattern of Saurogobio dabryi intestine in the lower reaches of Jialing River

To study the intestinal structure characteristics and the relationship with its growth pattern of Saurogobio dabryi, a total of 233 individuals were collected from the lower reaches of the Jialing River (Hechuan section) from 2015 to 2016. Morphological observation results showed that the intestinal structure of S. dabryi was Z-shaped, and belonged to carnivorous fish gut according to its relative short gut length (RGL) index (0.612 8). Based on its morphological structure, the intestine could be divided into three parts, the foreintestine, the midintestine and the hindintestine, with obvious difference in external morphology, internal structure and intestinal index. The growth pattern of S. dabryi intestine was allometry, with 2-year growth inflexion age and 145.07 mm corresponding fish total length (TL). Before and after the inflection point, there was different growth pattern of intestine, i.e., from the fast growth stage to slow growth stage. Meanwhile, the growth pattern of intestine was different between each part. In addition, the results of segmented analysis with R software showed that all of the inflexion points among three parts appeared at the age of 2 years, and their TL were 126.00 mm, 169.00 mm, 148.16 mm respectively; there were obvious differences in intestinal growth pattern among the three parts, with isokinetic growth in the foreintestine and the midintestine, but with significant allometric growth in the hindintestine, which had a fast growth stage before growth inflexion point and then changed to isokinetic growth pattern, based on the growth indices difference analysis between two stages. Thus, the difference of growth pattern of S. dabryi among the three parts of intestine might be related to their functional differentiation. Before the inflection point, the S. dabryi might improve their feeding frequency by the fast growth stage of the hindintestine, to meet the great demand for energy during the initial growth stage. The results obtained from this research can not only provide important scientific evidence for artificial cultivation of S. dabryi, but also offer a new example for studying the relationship between the growth pattern of fish intestine and its feeding habits.