That's right. They look nothing like a piranha. But they're hungry like a piranha. 
Critters 4 is directed by Rupert Harvey and collectively written by Barry Opper, Joseph Lyle, and David J. Schow. It stars Don Keith Opper, Brad Dourif, Angela Bassett, Anders Hove, Terrence Mann and Paul Whitthorne. Music is by Peter Manning Robinson and cinematography by Thomas L. Callaway.
The original wave of the "Critters" film series saw 4 films crammed into 6 years, with the decline in quality of each one reaching its nadir with this part 4. Gone is the funny asides that once blended seamlessly with the bloody antics of the razor teeth furballs, in place is a dull "Alien" clone that renders the Critters as bit part players in the series baring their name. In fact the makers have completely jettisoned one of their best forms of attack - the ability to fire lethal spikes from their personage.
Still, the cast remains a curious point of interest, what with two Oscar nominated actors working for food. The simple spaceship interior design is effective for the "stalk the prey" story axis, and the cinematography is pleasing for genre tropes. But really this is just a completist piece, and ultimately just one for those who began watching - and having fun - back in 1986 with the first film. 3/10