The Effect of Chronic and Acute Temperature Exposure on the Antarctic Notothenioid Trematomus bernacchii during Hypoxia Exercise and Feeding
Degree GrantorUniversity of Canterbury
Degree NameMaster of Science
Antarctic fish from the Perciform suborder Notothenioidei inhabit arguably the most thermally stable ocean environment on earth. In order to populate the subzero environment Antarctic fish have evolved numerous adaptations. However, specialisation to -1.9°C has incurred a trade off, thermal flexibility is lost likely due to modifications to the cold and as a result Notothenioidei are extremely stenothermic. Climate change mediated warming is predicted to increase the ocean temperature surrounding the Antarctic continent by 2°C within the next century. This increase is projected to affect individuals, populations and the community structures of those inhabiting the area and therefore the physiological study of the acclimation ability and thermal limitations of Antarctic fish is an area scientific interest. The present study is a series of discrete experiments relating to one species, Trematomus bernacchii, a circumpolar benthic Notothenioidei found in nearly all inshore waters surrounding the Antarctic coastline. These studies included investigation of the response of this species to both chronic and acute temperature exposure prior to and following a feeding event, a reduction in environmental oxygen and an exhaustive exercise event, as well as examination of T. bernacchii ability to recovery from these challenges. T. bernacchii demonstrated variable success when acclimated to +3°C. Failure appeared to be determined by the recovery period following capture and aquarium housing, 7 days housing following capture resulted in 100% mortality, conversly 3 months resulted in 100% survival. Following successful acclimation T. bernacchii showed physiological adjustment as acclimated resting metabolic rate mirrored that of T. bernacchii tested at environmental temperature, 20.63 ± 1.3 compared to 22.38 ± 1.02 mg. O₂. kg⁻¹. h⁻¹. The previously undefined specific dynamic action response (SDA), in T. bernacchii was characteristic of polar species. At environmental temperatures SDA scope was small 14.52 ± 3.52 mg O₂. kg⁻¹. h⁻¹, and lengthy ,72 hours; SDA duration was reduced to 9 hours in acclimated fish. Resting metabolic rate was elevated following acute exposure to +3°C, 34.27 ± 2.35 mg O₂. kg⁻¹. h⁻¹, masking the SDA response and associated parameters. T. bernacchii were relatively sensitive to hypoxia, Pcrit over four acute temperature exposures, ranged between 69 and 102mmHg, higher than the average range for teleosts (40 – 60 mmHg). Above -1°C Pcrit increased, rising with acute temperature exposure. Ventilation rate was temperature dependent and completely absent at +4 and +6°C. A bradycardia (beginning at 60 and 70mmHg) was observed at all temperature exposures, this response was consistent as all heart rates reduced by 25%. Recovery from both hypoxia and acute temperature exposure was rapid. Following an exhaustive exercise event aerobic Scope of T. bernacchii was constrained over an acute temperature increase, reducing from 38.58 ± 5.64 to 24.41 ± 4.92 mg.O₂. kg⁻¹.h⁻¹ over a 7°C temperature increase, respiratory scope too was reduced such that at +4 and +6°C scope was absent. Heart rate of T. bernacchii was highly constrained at -1°C, increasing by 2.54 ± 0.9 bpm following exercise. Acute temperature increase resulted in an increase in cardiac scope, maximum 6.29 ± 1.2 bpm at +2°C, due likely to a thermally mediated loss of cholinergic tonus following exhaustive exercise. Recovery of all parameters was temperature dependent and rapid upon return to -1°C. The present study is the first to quantify and assess the effect of acute and chronic temperature exposure on the SDA response of T. bernacchii. Furthermore, it supplements the current literature on acclimation ability, acute temperature exposure, aerobic scope and hypoxia tolerance for this species. This work will be of use in future investigations of the effects of rapid climate change on Antarctic notothenioid fish and the interconnected ecosystem.