The underwater fishing scenes were not simulated and the fish were actually killed.
The original English dub in theaters and on Video actually featured the voices of Susan George and Fiona Lewis, both of whom were the two British tourists in the film. However, this dub was later lost to history and a new one was created with American voice actresses, which was the one used on the DVD.
Due to the censorship imposed by the Mexican government at the time, there were two versions of the film prepared - the so-called uncut version, with plenty of explicit nudity, for foreign markets, and a cut version for domestic (Mexican) exhibition. It's now possible to find both versions on DVD.
One of a cycle of 1980s and mid-late 1970s movies that got made after the box-office success of Jaws (1975). The films include that movie's three sequels, Jaws 2 (1978), Jaws 3-D (1983), and Jaws: The Revenge (1987), as well as Orca (1977), Piranha (1978), Tentacles (1977), Killer Fish (1979), Barracuda (1978), Tintorera: Killer Shark (1977), Blood Beach (1980), Piranha II: The Spawning (1982), The Last Shark (1981), Up from the Depths (1979), Humanoids from the Deep (1980), The Island of the Fishmen (1979), Devil Fish (1984) and Mako: The Jaws of Death (1976).
Quentin Tarantino paid tribute to this movie at the 8th Morelia International Film Festival, showing a copy from his private collection.