Use of dried blood spots (DBS) to diagnose hyper- and hypoglycaemia in farmed dusky kob Argyrosomus japonicus in South Africa

Biomarkers require sensitivity and rapid turnover for health assessment of individuals and populations. Blood glucose in fish shows sensitive and measurable changes in response to environmental, physiological or nutritional stressors. Argyrosomus japonicus is currently the only commercially produced marine aquaculture finfish species in South Africa, yet knowledge about its responses to biological and environmental stressors is limited. Herein we confirm the utility of the Accu-Chek® Active diabetic glucometer under field conditions to provide accurate blood glucose data for A. japonicus, in comparison with laboratory-based enzymatic analyses using plasma, whole blood and dried blood spots (DBS). Glucometer, whole blood and DBS glucose was correlated with plasma glucose (R2 = 0.973, R2 = 0.955, R2 = 0.898 respectively). Whole blood glucose was consistently and significantly lower than plasma glucose, thus indicating that more complex sample preparation than storage on ice and freezing at − 80 °C are required to inhibit glycolysis in whole blood samples and generate accurate results. Diabetic glucometers offer a means to measure on-farm blood glucose with sufficient accuracy and rapidity. We include an analysis of a subsequent sampling from the farm, and demonstrate that through routine glucose measurements we were able to identify hypoglycaemia at the farm level, and that this corresponds to decreased condition of fish. The ease of DBS storage and stability of metabolites offer the opportunity of expanding fish health and condition monitoring by measuring multiple indicators in DBS.