Here's some info I found on a pet store's website. I don't know how accurate the info is.
Vampire Tetra
Scientific Name: Hydrolycus scomberoides
Recommended Aquarium: 100+ Gallons
Approx. Adult Size: 18 to 24 inches
Temperament: Aggressive
Ease of Care: Moderate
Diet: Carnivore
Native Waters: South America
An aggressive and carnivorous fish that requires heavy filtration and regular water changes to maintain. This fish is also known as the Saber Tooth tetra, and can get very large in captivity with the possibility of reaching several feet in length and a weight of 30 or more pounds. The Vampire Tetra requires a temperature in the range of 75 to 80 degrees. It is a live fish eater, so a constant supply of guppies or rosy reds will be needed as a food supply. Some of these fish can be converted to eat meatier frozen foods, but should still be offered live food as a supplemental source of nutrition.