The fen is an intelligent, man-sized fish, which walks about on 2 stubby fins when on land. It has both lungs and gills and may remain out of water for up to 24 hours. Its translucent skin makes the fen invisible when under water. Fens collect and use all manner of weapons and may also use their tail as a club which does 6 dice (d6) of damage if it hits. They are completely resistant to radiation, have a poison resistance of 18, reflect heat and light (laser) attacks for 5 melee rounds before taking damage, and can shapechange into a large bird and fly away if the going gets rough.

The Fen are a tragically doomed species, unfortunately for them word has been spreading across Gamma Terra as to how tasty their flesh is. The Fen became aware of this after a tragic incident when one of their exploration missions became cut off and ran out of supplies and had to turn to eating their dead comrades. On returning home the survivors became serial killers, until eventually the enforcers figured out what was happening and put a stop to it. Since then the Fen leaders decreed that any who spread word of that incident or the deliciousness of Fen flesh should be terminated to prevent the spread of the information.