Board Thread:Versus Debates/@comment-26005711-20150530210611/@comment-3965545-20150611022723

Found the lines from chapter 148 page 7 "Kisame: Why did we have to retreat...? With your power... Itachi: There's no need to be impatient... None. Besides which I must also... rest my body in one place for the foreseeable future. For not only Tsukuyomi, the nightmare realm... But I was forced to use the Amaterasu as well..."

another line

"Kisame: Hm....after all that the fool's spirit is intact...meanwhile you've overused those eyes of yours, you know that's dangerous." Implying it is bad for his health, meaning he is indeed sick besides getting tired and eyesight getting weaker, as it only made Sasuke tired and left his eyesight weaker each time.