Nope. Taxonomically, both are in the Animal Kingdom, but that's where they diverge. Fish are in the Phylum Chordata (more or less having a spinal cord). Octopi, or pus-fellers as Quarrel called them, are mollusks - no backbone, inter alia. Culinarily, prepping fish vs octopus is very different. read more
Culinarily, prepping fish vs octopus is very different. Once you have them prepped (which includes simmering octopus a good long time to tenderize it), you can cook them in some of the same ways - grilled/broiled, in ceviche, etc. read more