This sentence contains two figures of speech. Figures of speech express an idea by making a picture of words. "I smell something fishy here." Its basic meaning is "I smell a rotten fish" This means one detects or suspects something suspicious about someone, someting or situation. Now let's look at the first one. "a faint whiff" means one can detect something but only a little bit. Whiff is smell or odor. So more than a faint whiff means one can see something quite clearly. Let's look at the second one.There is an expression "Like shooting fish in a barrel." Now it is really easy to shoot fish in a barrel, they have nowhere to hide and no escape. So this means it is easy to do something. The sentence then means I see that it will be really easy to do something. Hope this helps John

Could you give the context of the sentence? Because it could mean anything depending on who or what said it.