The gills are spaced close together, with between 16 and 26 gills reaching the stipe, and there are up to three tiers of interspersed lamellulae (short gills that do not extend fully from the cap edge to the stipe).

There are short sensory barbels around the head, together with short, backward pointing spines on the gill covers.

Breathing is the process that moves air in and out of the lungs, or oxygen through other breathing organs such as gills.

The olm breathes with external gills that form two branched tufts at the back of the head.

The nerve's route would have been direct in the fish like ancestors of modern tetrapods, traveling from the brain, past the heart, to the gills (as it does in modern fish).

In fish, the system has only one circuit, with the blood being pumped through the capillaries of the gills and on to the capillaries of the body tissues.

These factors include restrictions on trawl fishing from 1991 followed by its total prohibition in 1993 the imposition of seasonal restrictions on fishing of certain commercially important species and the standardization of gill net mesh size for various species.