Utilization of a portable glucometer for the measurement of tissue glucose as a stress indicator in ornamental fish

Abstract

The stress response in vertebrates is determined by measuring cortisol production following acute or chronic exposure to various environmental stimuli. Cortisol assays as responses to stressful events are done on blood samples using ELISA or radio-immunoassays. However, these procedures require expensive reagents and special equipment that are not available to most fish growers or hobbyists. A portable glucometer, which is a point-of-care (POC) device to monitor blood glucose levels, was assessed in terms of its usefulness in assessing the stress response in vertebrates by quantitating whole body (tissue) glucose. Using ornamental fish as our model species, glucose levels from tissue homogenates were measured in swordtail (Xiphophorus hellerii) following handling stress by exposure to air for 3 min. Tissue glucose was measured before air exposure (control), immediately after air exposure for 3 min, and at 30 min post-air exposure (recovery). There was an increase in tissue glucose immediately after exposure of the fish to air for 3 min. At 30 min post-exposure, the levels of tissue glucose were still elevated, but may be moving towards returning to the pre-air exposure levels (control), which were measured prior to the application of the stressor. Our results have shown that a portable glucometer has good potential in monitoring stress response in vertebrates using ornamental fish as a model by quantifying tissue glucose in lieu of a more expensive cortisol assay.