The pike-cichlid, an important predator (and selective agent) of the guppy, Poecilia reticulata. I never knew that there were people so enthusiastic about this "kewl fish". There's a bit of confusion about the taxonomy of these fish out there; the name sometimes gets misspelled as "Crenichla" and pretty much anything in the genus "Crenicichla" counts as a pike-cichlid. Fishbase.org doesn't mention any controversy about names, as far as I could see. C. saxatilis has also been identified as an important guppy predator. This image comes from here, and is tentatively identified (apparently) as either C. alta or C. lepidota.
Apparently, basic HTML tags like [I] work in titles in Blogger. Good, I was getting mildly annoyed with my violation of scientific convention in species names.