Here are two articles on fish intelligence I've read recently, though the first is problematic in terms of writing (overblown results language in the title and first couple paragraphs) and in terms of non-ideal (cruel) experimental processes. Watching fish suffocate alive on ice in a seafood store in Florida instigated my vegetarianism, actually.
I feel like there's a new groundswell of acknowledgement regarding animal sentience and intelligence happening lately in the academic arena, and I'm digging it. Here's Dr. Frans B.M. de Waal discussing his perspective in "What I Learned From Tickling Apes," published in The New York Times.
I'm now more than halfway through Carl Safina's Beyond Words (I discussed my interest in the book previously in this post) and the experiences and information he relates are very powerful messages about animal intelligence. A much shorter but no less potent read is one of this week's The New York Times Magazine articles entitled "What Does a Parrot Know About PTSD?"
I've long believed that many people, either consciously or subconsciously, choose to deny the breadth and depth of animal intelligence out of guilt about their own practices and values. Eating meat, supporting factory farming, purchasing leather/ivory/horn/bone products, damaging the environment, keeping pets in traumatic conditions as per the article (and judging animals solely as property in the eyes of the law) - these types of decisions are easier to explain away when the victims aren't sentient.