Metabolism and enzyme activities of hagfish from shallow and deep water of the Pacific Ocean

Although hagfishes are ecologically important members of benthic communities there has been little data available on their metabolism. The oxygen consumption, enzyme activities, and muscle proximate composition of shallow living Eptatretus stoutii and deeper living E. deani were measured to investigate hagfish metabolism. Very low rates of oxygen consumption and both aerobic and anaerobic enzyme activities in the body musculature confirmed the low metabolism of hagfishes. However, significant variation in oxygen consumption existed. E. stoutii had significantly lower rates compared to those of the deeper living E. deani and two other shallow living species for which literature data was used. Both species could regulate their oxygen consumption to very low oxygen concentrations. Epatretus deani, which lives in an oxygen minimum zone, had a significantly lower critical oxygen tension (0.83 kPa) compared to E. stoutii (1.47 kPa). The deeper E. deani had greater lipid stores than E. stoutii which may reflect its deeper habitat and more sporadic food supply.