Pupil size variation as a response to stress in European catfish and its application for social stress detection in albino conspecifics

Abstract

Hormonal changes such as increased cortisol level in blood plasma in response to stress and social environmental stimuli are common among vertebrates including humans and typically accompanied by other physiological processes, such as changes in body pigmentation and/or pupil dilatation. The role of pupil size variation (PSV) as a response to stress have yet to be investigated in fish. We exposed albino and pigmented European catfish to short-term stress and measured changes in pupil size and cortisol level. Albinos showed lower pupil dilatation and higher cortisol levels than did pigmented conspecifics. A clear positive relationship between pupil dilatation and cortisol concentrations was observed for both pigmented and albino specimens, suggesting that PSV can be used as a stress indicator in fish, irrespective of albino’s inability to express social communication by coloring. During the follow-up, we investigated whether a penultimate contest between albino individuals would impact contestants’ social stress during subsequent contact. We observed PSV during the contact of unfamiliar albino catfish with different penultimate experiences (winner (W) and/or loser (L)). Then, the following treatment combinations were tested: WW, WL and LL. Twenty-four-hour contact of two unfamiliar catfish resulted in higher pupil dilatation among individuals with previous winner experience. Among treatment combinations, a WL contest displayed the highest pupil dilatation for winners. PSV reflected socially induced stress in individuals that was accompanied by the “winner” experience and dominancy in albinos. To conclude, the present study validates pupil dilatation as a non-invasive method to evaluate stress level in pigmented as well as albino fish in various contexts.

The eyelid and pupil dynamics underlying stress levels in awake mice

“…Instead of measuring corticosterone level or recording respiration/heart rate as the stress biomarkers, we assessed the dynamic changes of the pupil due to its non-invasive and non-physical contact to the conscious animals. Furthermore, stress-induced changes in pupil size and shape have been suggested to be resulted from the activation of the autonomic nervous system's sympathetic branch [27,28]. Therefore, the pupillometry, on the one hand reflects the stress levels during training, and on the other hand, indicates the activities of the 10 sympathetic nervous system while imaging.…”

Pupillometry to show stress release during equine sports massage therapy

“…Several previous studies connected the level of stress and pupil diameter 14 – 16 , 18 , 19 . Pedrotti and coworkers 15 recorded pupil diameter during a simulated driving task.…”

“…Stress leads to increased blood cortisol levels. A study in catfish showed that the pupil's diameter correlates with the blood cortisol levels 19 . The authors showed an increased pupil size and heart rate while completing a time-sensitive task.…”

“…A good correlation between blood cortisol level and pupil diameter exists in fish. An increased cortisol level, typically seen under stress, increases pupil diameter 19 .…”

Awake Mouse fMRI and Pupillary Recordings in the Ultra-High Magnetic Field

“…Interestingly, pupillometry, a non-invasive indicator of altered arousal (Bradley et al, 2008 ), vigilance (Ebitz et al, 2014 ), emotion (Partala and Surakka, 2003 ), and cortical states (Reimer et al, 2014 ), has been combined with fMRI studies of human and animal brains (Murphy et al, 2014 ; Schneider et al, 2016 , 2018 ; Pais-Roldan et al, 2020 ; Sobczak et al, 2021a ). Importantly, there are quite a few literatures to show the stress linkage with pupil size in fish (Slavik et al, 2020 ) and humans (Schneider et al, 2016 , 2018 ; Schneider, 2018 ), as well as the cognitive (attention) demand with pupil size changes. The measurement of concurrent fMRI and pupil dynamics in awake mice remains to be established to further decipher the global functional basis underlying different pupil dynamic spectrums(Sobczak et al, 2021a , b ).…”