KIDDER, G.W.,III*; GOLDSMITH, C.E.; NEVILLE, M.J.; PETERSEN, C.W.; PRESTON, R.P.; Mt. Desert Isl. Bio. Lab, Salisbury Cove, ME; Illinois St. Univ., Normal, IL; Illinois St. Univ., Normal, IL; College of the Atlantic, Bar Harbor, ME; Illinois St. Univ., Normal, IL: Basal Oxygen Consumption in Fundulus heteroclitus

The basal oxygen consumption of F. heteroclitus is needed for further investigations of the energetics of osmoregulation. We used flow-through respirometry, bubbling gas through the water containing the fish, through a drying tube to remove water and carbon dioxide, through an oxygen sensor and a mass flow meter, both read every 15 seconds by a computer. During each 24 hour run, a solenoid valve bypassed the fish chamber 20 times for 7.5 minutes each, to recalibrate the oxygen sensor. Thus 20 readings of Q_O2 (ml O₂/kg�hr) were obtained per 24 hour period while holding the oxygen tension within 0.5% of its target value. Fish were acclimated to seawater and tested in seawater. Q_O2 decreased over 50% during the first 12 hours in the chamber, remaining constant thereafter; the values from 12 to 24 hours after any change are taken as the basal rate in that condition. We find that oxygen consumption is a function of temperature (Q₁₀ = 2.65) and of fish size, as expected. We searched for circadian or tidal rhythms in respiration without finding any. We have determined the effect of lowered oxygen tension on Q_O2. At 10.5 C, 50% inhibition occurs at about 5% oxygen, with excellent 24 hour survival. We calculate a minimum ventilation rate of 12.09 � 0.58 ml water/kg fish�hr in air, which is increased to 26.01 � 2.68 in 5% oxygen. This is consistent with the widely held assumption that low oxygen availability might impose limits on adaptation to other stressors such as osmotic challenges. This suggests a method for increasing the energy demand due to osmotic work. [Sup. by NSF-CRUI 0111860 to RLP, GWK and CWP]