Husbandry stress of zebrafish, Danio rerio.

摘要

Zebrafish, Danio rerio, are widely used as vertebrate research organisms yet little is know about their responses to husbandry stressors. This dissertation examined the whole-body cortisol responses of zebrafish to husbandry stress. Additionally, the effects of stress on the susceptibility to mycobacteriosis and microsporidiosis (Pseudoloma neurophilia) were determined including effects on growth and reproduction. In Chapter 2, crowding increased cortisol but this was modulated by fasting and feeding; fasted but not fed fish elevated cortisol when crowded. Fish weight was inversely related to cortisol level in fasted, crowded fish. In Chapter 3, zebrafish rapidly responded to net handling stressors with a 6-fold increase in whole-body cortisol which peaked at 15 min post-net-stress. Cortisol recovered to control levels by 60 min. The variability in resting cortisol increased with fish age. In Chapter 4, fish infected with Mycobacterium marinum and subjected to husbandry stressors had 14% cumulative mortality over 8 weeks while no mortality occurred among infected fish without stress. Stressed fish, injected with M. chelonae were 15-fold more likely to be infected than non-stressed fish. Sub-acute, diffuse infections were more common among infected fish that were stressed than those not stressed. In Chapter 5, we examined the effects of stress on pre-existing and experimental Pseudoloma infections and the subsequent effects on survival, growth, and reproduction. Stress increased mortality and myositis in fish with pre-existing infections. There was no mortality among fish experimentally infected with Pseudoloma regardless of stress treatment. The onset of infection occurred sooner in stressed fish and stress significantly increased the mean intensity of infection. Weight decreased in stressed and experimentally infected groups from week 13 to 20 post-exposure but not in the control group. Fecundity was negatively related to mean parasite area among Pseudoloma-infected and stressed fish. Whole-body cortisol is an indicator of crowding and handling stress in zebrafish. Husbandry stressors exacerbated mycobacteriosis and microsporidiosis in zebrafish with associated reductions in growth and fecundity. Zebrafish are hardy and well adapted to a laboratory environment. Nevertheless, reducing stress should aid in preventing disease outbreaks and maintaining growth and fecundity of this popular laboratory fish species.