Health, condition, and survival of creek chub (Semotilus atromaculatus) across a gradient of stream habitat quality following an experimental cortisol challenge

Abstract

Urbanization and agricultural practices can lead to alterations in stream habitat quality. However, there have been few attempts to understand if these alterations influence the health and condition of fish, or their ability to respond to multiple stressors. This study examines a sentinel fish in streams adjacent to different types of land-use practices and how they respond to an experimental stressor. Creek chub (Semotilus atromaculatus) from replicate agricultural, urban, and reference streams were subjected to an experimental manipulation of cortisol, the primary stress hormone in fish. A single intraperitoneal injection raised circulating plasma cortisol for ~3 days, mimicking the physiological effects of a prolonged stressor. We compared the survival, health, and condition of cortisol-treated, sham-treated, and control fish across the different land-use types. While marginally non-significant (P = 0.06), cortisol-treated fish displayed an ~50% increase in mortality in streams adjacent to agricultural areas. We did not observe differences in blood glucose, condition factor, splenic index, and gonadosomatic index, or parasite burden among the treatment groups or relative to land-use type. However, within the agricultural watersheds, the hepatosomatic index value of fish receiving a sham treatment was ~20% greater than fish in the control treatment, a significant result that appears to be spurious given that a similar effects was not observed in other land-use types. Overall, these results suggest that in the wild, there are apparently compensatory mechanisms that enable creek chub to persist despite being exposed to a significant challenge with little evidence that the outcome is modulated by variation in habitat quality, at least among the three types of sites (i.e., urban, agricultural, and reference) studied here. Nonetheless, we encourage additional field-based studies with larger sample sizes or better recapture rates to improve statistical power and provide more clarity on how variation in habitat quality influences how fish respond to other challenges.