On Feb. 15, 2012 Ufotable and Aniplex released an hour and ten minute long OVA (Original Video Animation) of Gyo, based on the manga.
Though the theme of walking fish and the death stench is still the same, the rest of the plot drastically differs from the manga. Notably, Kaori is the main character of the anime instead of her boyfriend.
"The friends Kaori, Erika and Aki are on a vacation to celebrate their upcoming graduation, when suddenly an infestation of mysterious walking fish forces them to reevaluate everything they care about in order to stay alive." IMDB