Gammarus sp. is an amphipod crustacean genus in the family Gammaridae. It contains more than 200 described species, making it one of the most speciose genera of crustaceans. Different species have different optimal conditions, particularly in terms of salinity, and different tolerances. 
These were raised in freshwater but can be used as food for saltwater fish.
You can choose between 50, 75 and 100 counts