¹⁴C-glycine uptake by fish scales: Refinement of a growth index and effects of a protein-synthesis inhibitor

In vitro 14C-glycine uptake by the scales of bluegill Lepomis macrochirus was sensitive to the pH of the incubation medium; maximum uptake occurred at approximately pH 7.7. Cycloheximide, an inhibitor of protein synthesis, reduced glycine uptake by up to 90%, providing further evidence for the involvement of glycine uptake in the process of protein synthesis. The minimum duration of handling stress that resulted in a significant change in glycine uptake was 60 minutes; after 240 minutes of continuous stress, glycine uptake was reduced 62% from control values. Diel sampling of laboratory fish indicated no daily rhythm in glycine uptake and demonstrated a significant correlation (r = 0.837) between glycine uptake and fish growth rate as estimated over a 2-week interval. The results of these experiments suggest that glycine uptake by scales can be a reliable index of fish growth or state of stress.