Schlock horror films often star aquatic predators, from a toothy fish burping out a masticated human penis in Piranha, to the toy-like leviathans of Mega-Shark Versus Giant Octopus. A lot of GYO: Tokyo Fish Attack! is on that level; which is to say, hilariously stupid and offensive. The film finds its level barely ten minutes in, when a horny girl is preparing for a threesome. A walking shark gatecrashes the action and tears her dress off. Well, you wouldn't want to eat your food with the wrapper on.

The source Gyo horror manga by Junji Ito (published in two books by Viz Media) was far smarter than this. It was ludicrous, but also haunting and increasingly surreal, its lyrical pathos undercutting the story's cruel cynicism. Nearly all that has gone in the film, except for some moments of grandiose weirdness in the last minutes. It's a perversely odd adaptation, making humungous changes to the manga's story and characters, yet cramming in as many of its key images as possible. Given the anime is only seventy minutes long, that means a choppy, randomly paced story. Then again, few films throw so much at you so fast. There are tacky sex scenes; plane and train crashes (the plane one is genuinely impressive); mad Frankenstein scientists; mutants with killer farts and bad breath; freaky circus ringmasters; and even a naughty-tentacles octopus taking a bow.

Gyo's big laughs come in the non-monster scenes. The moments when characters explain their tragic backstories are funny in an Airplane way, and apparently meant as such. A mad scientist who turns up late in the film is played openly for laughs, all wacky poses and framings. The fishy fiends are far clunkier on screen, with lots of clumsy CGI, stiff animation and badly staged action. For all the burning buildings in the background, you rarely see the monsters chowing down or actually causing the carnage. Heck, there were more murderous fish when an invasion of walking dolphins infested Springfield in one of The Simpsons' “Treehouse of Horror” specials.

The ugliest violence in Gyo is human, a brutal attack by one female character on another, which feels even grosser given the tameness of the monsters. This girl-on-girl assault takes place in the midsection of the film, which is surprisingly affecting as Gyo's leads each go through emotional meltdowns. To spice up the emotional subtexts, the fish monsters infect humans by spiking them with their metal feet, and the infection is not pretty. The subtitles repeatedly refer to the creatures “spearing” the girls, two of whom may be virgins, and one who definitely isn't; guess who comes out worst. It's debatable if Gyo owes more to Jaws or to a sex-is-death slasher like Halloween.

Gyo is animated by ufotable, a studio that's still in the process of making its own name. ufotable produced Fate/Zero, and a few older anime including Coyote Ragtime Show and the Tales of Symphonia OAVs, but the bulk of its credits is in in-betweening. As a piece of dirty exploitation, Gyo must have seemed a soundly commercial film for the studio, but the fact that we're getting it on DVD before America doesn't bode well for its foreign sales. For older British anime fans, Gyo will look like nothing so much as an update of the sex-and-violence product licensed en masse in the 1990s; what Mike Preece, one-time MD of Manga Entertainment, called anime for the “beer and curry” crowd.

The film is released not by Manga but Terror-Cotta, the horror DVD label of Terracotta Distribution, which needs to look at its quality control issues. Understandably, the film is subtitles-only, though the title menu offers the exciting option to “Play Movie Without Subtitles”! You might be tempted, as the subtitles are full of solecisms and howlers. In one scene on a plane, an announcer is subbed as saying, “We are preparing for landing,” when the characters are still waiting on the runaway! Such sloppiness makes you question the suspiciously incongruous bits of translation. When the demure heroine unexpectedly whispers “What the fuck was that?,” is it a fair translation of the Japanese dialogue or a bit of old-school fifteening?

The disc carries a few minutes of footage relating to the Terracotta Film Festival – though they don't relate to Gyo – plus an interview with Junji Ito, creator of the original Gyo manga. Alas, the interview amounts to three screens of large text. From them we learn little except that Ito is a huge Beatles fan, and listens to their music while he's drawing his horror manga. Whether Ito is equally stimulated by the anime film of his work – or indeed, if he's even bothered to see it – is not revealed.