The real reason I chose "deadfish":
At the time I was chosing a username, I had recently spoken with my Uncle Peter. I have fond memories, circa 1970, of disecting live sharks, know as "dogfish" where I grew up, on the beach as anatomy lessons with Uncle Peter who is a physician. Deadfish sounds like dogfish. Who needs a logical reason to chose a username anyway?
Other oblique reasons:
Ever since I was a kid, for the past thirty years, I have kept all sorts of freshwater tropical fish aquariums, AND, I have had more than my share of deadfish ;-).
Or, I spent the majority of my childhood living on a bay, near Poulsbo, Washington, which when my dad was a kid, was called Dogfish Bay. My Uncle David (or was it Uncle Bill) tells a story of when he and my Dad used to wad newspaper into a huge pile floating on the water in the bay at night. They set this on fire, and the light from the bonfire would attract dogfish. They then would club to death the dogfish for fun, as precocious boys are known to do... [not politically correct and not much better than discecting them live...]
"deadfish" also is an oblique reference to the Dr. Seuss rhyme "old fish, new fish, red fish, blue fish...".
It also is a play on words with "dead" from "deadhead" [as in Grateful Dead fan] and "Phish", which is a rock band which has many of the same fans as the Grateful Dead, and plays music which is sometimes similar.
Not to mention that I like the idea of a large number of potentially associated words, such as bigfish, badfish, dogfish, catfish, sailfish, sunfish, gladfish, sadfish, oldfish, newfish, redfish, bluefish, etc..