Hi Nisar

Actually your question is a little bit vague. If you talk about specific fish species and its natural diet, yes it might change. Food item might change because their availability will change. However it does not mean that a carnivorous fish turn to a herbivorous!, bottom feeding behavior change to phytoplankton filter feeding Or ... 

So I think it is better to describe your case with more details..  

You need to radically refine and clarify your inquiry, Mr. Nisar. One of the biggest causes of fisheries mitigation failure in hydroelectric projects is that even in the unlikely case that the adult migrants can make it past the dams through the fish ladders, the vastly different environment of the impoundment upstream of the dam —representing a change from the previous "lotic" hydroecology to a new "lentic" system— is typically far outside the adaptive evolutionary history of both the ichthyfauna and of the organisms on which they would have typically fed, pre-project.

I have not worked in the tropics, but for boreal lakes and streams the answer is yes; at least for functional feeding groups of littoral invertebrates in lakes and riffle invertebrates is streams. For example, see Johnson R.K., Goedkoop, W. and L. Sandin. 2004. Spatial scale and ecological relationships between the macroinvertebrate communities of stony habitats of streams and lakes. Freshwater Biology, 49: 1179-1194.