A Nikkatsu presentation of a Sushi Typhoon, Stair Way production. (International sales: Nikkatsu, Tokyo.) Produced by Yoshinori Chiba, Toshiki Kimura. Executive producer, Akifumi Gugihara. Directed by Sion Sono. Screenplay, Sono, Yoshiki Takahashi.With: Mitsuru Kukikoshi, Denden, Asuka Kurosawa, Megumi Kagurazaka, Hikari Kajiwara, Tetsu Watanabe.

Although reportedly based on a true story, with its buckets of blood, screechy thesping and pervy air of hysteria, horror pic “Cold Fish” couldn’t easily be mistaken for anything other than what it is: another fervid fantasia hatched by cult Japanese helmer Sion Sono (“Suicide Club,” “Love Exposure.”) Yarn about a milquetoast fish store owner who gets sucked into the orbit of a psychotic serial killer and his equally wacko wife is, like most Sono pics, too long. But its gleeful humor and dare-you-to-watch aesthetic will help it rack up kills at specialty fests, and skewer followers on ancillary.Tropicial-fish store proprietor Shamoto (Mitsuru Kukikoshi) lives in an unhappy home. His spoiled, disobedient teenage daughter Mitsuko (Hikari Kajiwara) loathes her tarty stepmother Taeko (Megumi Kagurazaka), who’s not much older than Mitsuko. One night, Mitsuko is caught shoplifting in a supermarket, but another customer, Murata (Denden), the owner of a much larger fish store, talks the supermarket out of pressing charges by offering to help the girl go straight with a job and a place to stay at a dormitory attached to at his business.

At first, everyone is delighted with the new arrangement, but the unnervingly over-friendly Murata, who has his own hot bride, Aiko (Asuka Kurosawa), has a more sinister purpose in mind. Turns out, he’s killed scores of people over the years, sometimes to steal money but just as often for kicks — and Aiko, like some kind of Asian Rosemary West in slutty shoes, is just as turned on by murder. Obliged to visit Murata for helping his daughter, Shamoto witnesses him kill a man, then is blackmailed into helping dispose of the body — and later more bodies, which they cut up in graphic detail into little pieces in a mountain hideaway. (Sono perhaps misses a gross-out trick by not having them feed the leftover bits of corpse to his aquatic stock, as some auds might expect he would.)

Thesping is often turned up to too shrill a pitch, and indeed excessive levels at the projection caught didn’t help, but it’s all of a piece with the way-over-the-top nature of the material. More modulation on every level might have created a more suspenseful, exportable product, but “Cold Fish” can’t be easily dismissed a pure exploitative genre fare. There’s an interesting social satire of sorts going on here, although given the script’s ending, Sono seems to have a pretty deterministic, bleak view of human nature. All the same, in terms of surprises and little twists, the last reel’s a doozy.

Lensing by Shinya Kimura looks like it was done on either 16mm or lower-than-highest definition digital, creating a grainy, degraded look that matches the theme. Drum-heavy score enhances the pic’s assault tactics.

Camera (color), Shinya Kimura; editor, Junichi Ito; music, Tomohide Harada; production designer, Takashi Matsuzuka; costume designer, Satoe Araki; sound (DTS), Hajime Komiya; special effects supervisor, Yoshiro Nishimura; action designer, Tak Sakaguchi; line producer, Shinya Himeda; assistant director, Satoshi Yoshida. Reviewed at Venice Film Festival (Horizons), Sept. 7, 2010. (Also in Toronto Film Festival — Vanguard.) Running time: 145 MIN.

With: Mitsuru Kukikoshi, Denden, Asuka Kurosawa, Megumi Kagurazaka, Hikari Kajiwara, Tetsu Watanabe.