As he was ill, he had a dull appetite.

因为生病，他食欲不振。

With the expansion of host range, surface of fish becomes dull, mucus secretion increase more, and the fish become weaker due to loss of appetite.

随着寄生范围的扩大，体表失去光泽，粘液分泌量增多，鱼因食欲减退而变得虚弱。

Exercises dull our appetite.

运动使得我们没了胃口。