Background/Aims: Recreational angling exposes fish to sublethal physiological disturbance through exhaustive exercise, hooking and air exposure, disrupting acid–base balance and elevating stress biomarkers. Southern sand flathead (Platycephalus bassensis) is Tasmania's most heavily targeted recreational species, with most captured fish being undersized and released, and many likely recaptured multiple times over their lives. This makes post-capture physiological recovery directly relevant to the current state of the stock. This study characterises physiological disturbance and recovery in sand flathead following capture, under laboratory and field conditions.
Methods: Fish were sampled following laboratory-simulated and field-based angling at multiple post-capture timepoints (control, 0, 1, 3, 24, 48 hours). Whole blood was analysed for pH, pCO2, pO2, HCO3- and lactate via i-STAT with CG4+ cartridges, and glucose was measured with a handheld meter. Fish length and capture temperature were recorded throughout. Cortisol assays are underway to further characterise the endocrine stress response.
Results: Capture induced a clear respiratory acidosis, with pH depressed and pCO2 elevated immediately post-capture. Both moved back toward baseline within the first few hours. Glucose showed a rising trend across the field sampling series, though this did not appear as significant pairwise differences between individual timepoints. pO2 and HCO3- showed no clear group differences, and body length was not associated with any blood parameter. Field-captured fish showed a more pronounced initial disturbance than fish exposed to simulated angling in the laboratory.
Conclusion: Sand flathead show a fast correction of capture-induced acid-base disturbance, indicating this component of the capture response resolves within hours. Whether other aspects of the stress response, such as the observed rise in glucose and additional cortisol analysis, resolve on a similar or slower timescale warrants further investigation. The greater disturbance in field versus lab-captured fish further suggests simulated angling may underestimate the true physiological cost of capture.