The delimitation of intestine segments of koi carp (Cyprinus carpio var. koi) based on histological features

In this study, the delimitation of intestine segments of koi carp (Cyprinus carpio var. koi) was conducted using a histological approach with the measurements of height of mucosa folds (HF), width of mucosa folds (WF), thickness of muscularis (TM) and cross-sectional area (CSA). According to the change trends for these four parameters, the intestine of the koi carp was divided into anterior intestine, middle intestine and posterior intestine. The locations of the three intestine segments were defined, and their ratios along the entire intestine were accounted for 23.84 ± 1.18%, 46.77 ± 2.29% and 29.39 ± 1.65%, respectively. The anterior intestine had a significantly higher HF, compared with the middle (p < .01) or posterior intestines (p < .01). The muscularis became thin gradually from the anterior intestine to posterior part. TM was significantly different among the anterior, middle and posterior intestines (p < .01). The anterior intestine had a significantly higher CSA, compared with the middle (p < .01) and posterior intestines (p < .01), and the latter two segments had similar CSA values (p > .05). The procedure of the delimitation of the koi carp intestine segments can offer useful information for future studies on other fish species. The presented results are meaningful for studies on differential functions of the different intestine segments in fish.