Characterizing the hypoxic performance of a fish using a new metric: PAAS-50

The hypoxic constraint on peak oxygen uptake ((M) over dotO(2,peak)) was characterized in rainbow trout over a range of ambient oxygen tensions with different testing protocols and statistical models. The best-fit model was selected using both statistical criteria (R-2 and AIC) and the model's prediction of three anchor points for hypoxic performance: critical P-O2 (P-crit), maximum (M) over dotO(2,peak) and a new metric, the minimum P-O2 that supports 50% of absolute aerobic scope (PAAS-50). The best-fitting model was curvilinear using five strategically selected P-O2 values. This model predicted PAAS-50 as 70 mmHg (coefficient of variation, CV=9%) for rainbow trout. Thus, while a five-point hypoxic performance curve can characterize the limiting effects of hypoxia in fish, as envisaged by Fry over 75 years ago, PAAS-50 is a promising metric to compare hypoxic constraints on performance in a standardized manner both within and across fish species.

Automated summary

The hypoxic constraint on peak oxygen uptake was characterized in rainbow trout using different testing protocols and statistical models. The best-fit model was selected based on statistical criteria and the model's prediction of key hypoxic performance points. A curvilinear model with five strategically selected oxygen tensions was found to best describe the hypoxic performance of rainbow trout, with PAAS-50 as a promising metric for comparing hypoxic constraints across fish species.