Answer:
History
They were bred to be fighting fish and were used by Javier Hidalgo as death penalties against traitors. They were encountered during Operation: Javier by Leon Kennedy and Jack Krauser.
Biology
Compared to the Neptune, these had small improvements, namely that they could glide on the water, and were able to survive for a time on land. Aggressiveness was also heightened by the t-Virus.
Gallery