Early life stress and effects at subsequent stages of development in European sea bass (D. labrax)

Abstract

Abstract To investigate the effects of exposure to long term chronic mild stressors during early development on larvae and juvenile performance and cortisol stress response, an unpredictable chronic low intensity stress (UCLIS) protocol was developed for the first time and evaluated in European sea bass, Dicentrarchus labrax . UCLIS protocol was based on the unpredictability, variety, frequency and moderate intensity of the applied stressors, providing a relatively realistic model of everyday aquaculture husbandry practices. UCLIS lasted for 14 consecutive days, starting at different phases of early ontogeny (first feeding, flexion and development of all fins). Evaluation was performed through the determination of water-born cortisol concentrations of the larvae rearing tanks at regular intervals, recording of mortality and measurements of growth performance. In addition, its effects on subsequent developmental phases were evaluated by measurement of growth characteristics and by the determination of plasma cortisol in juvenile fish, prior and 30 min after the application of an acute stressor. Our data show that European sea bass larvae are sensitive to mild husbandry stimuli with consequences even at subsequent stages of development, with the stages of first feeding and all fins being the most critical, providing the necessity to reconsider common rearing practices. In particular, UCLIS application resulted in higher water cortisol release rates in all groups compared to the controls proved to be a reliable non-invasive indicator of stress even during early ontogeny. Performance of fish in terms of survival, total length and wet weight was also affected by the stress protocol, as larvae that had been exposed to UCLIS at the beginning of first feeding and the formation of all fins displayed worst performance compared to fish exposed to UCLIS at flexion and compared to the controls. Early life stress did not affect plasma cortisol levels of juveniles exposed to additional acute stressors. However, fish were very sensitive to common handling practice and in addition, significant higher plasma cortisol concentrations were found in juveniles exposed to UCLIS at the stages of first feeding and onwards to flexion and the formation of all fins and onwards to the development of melanophores, compared to the other two groups in accordance with the differences observed in growth rates. Concluding, our data show for the first time that common husbandry practices during early development have an impact both on larvae performance and at later stages of development, as life history affected growth and the stress response in juvenile fish.