3.4.1. Foregut

Table 2 shows that the lengths of foregut VL of coral trout in the different water flow velocity groups were significantly different (*p* < 0.05) and that the 1 bl/s water flow velocity group was significantly shorter than those of the control group and other water flow velocity groups (*p* < 0.05). The value of MS in the 2.5 bl/s water flow velocity group was significantly lower than in the 2 bl/s water flow velocity group (*p* < 0.05). The VT of coral trout in the 2 bl/s velocity group was the highest—significantly higher than in the control and other velocity groups (*p* < 0.05). The villous tissue structure of coral trout in each water flow velocity group was complete, but the number of goblet cells in the medium–high-water flow velocity group (2 bl/s and 2.5 bl/s) was reduced compared with the control group (Figure 4).

**Table 2.** Effect of water flow velocity on the index of foregut tissue of coral trout.


The values are average ± standard deviation of four replications (*n* = 6). Values of different letters mean significant difference among the groups (*p* < 0.05), and those with no letters mean no significant difference (*p* > 0.05).

**Figure 4.** The effect of water flow velocity on the foregut structure of coral trout. (**a**) Hydrostatic control group: intestinal tissue was normal, muscular thickness (MS), villus length (VL), and villus thickness (VT) were uniform, and there were many goblet cells (thick arrows); (**b**) 1 bl/s water flow velocity group: muscular thickness (MS), villus length (VL), and villus thickness (VT) showed no significant changes compared with the control group, while goblet cells (thick arrows) were smaller and their number was relatively reduced; (**c**) 2 bl/s water flow velocity group: the muscle layer was thinner than in the control, while the number of goblet cells (thick arrows) was relatively reduced and their size was smaller; (**d**) 2.5 bl/s water flow velocity group: the muscle layer was relatively thin, while the number of goblet cells (thick arrows) in the contrast photograph was relatively small, and the morphological distribution was uneven.
