Physoclist (also Physoclisti or Physoklisten ) is the name for a group of bony fish . In these, the swim bladder is closed, i.e. the embryonic connection between the intestine and the swim bladder ( ductus pneumaticus ) no longer exists in the fully grown (adult) state (in contrast to the physostomes ). With the Physoclists, gas exchange takes place via blood vessels that are closely connected to the swim bladder. The gas exchange is made possible by gas nozzles .