Why would a fish with faulty valves in its conus arteriosus probably suffer from a lack of energy?

A faulty conus arteriosus  would compromise on an effective gaseous exchange that keeps the blood of the fish oxygenated for respiration of tissues. The conus arteriosus is one of two accessory chambers found in most fish with two-chambered hearts. The primary function of the conus arteriosus is to prevent the backflow of blood and keep a steady flow of blood into the ventral aorta and the gills.

answer: substrate concentration. enzymes work best when there is a high enough substrate concentration for the reaction they catalyse.