Communications: Fish-to-Fish Testosterone Transfer in a Recirculating-Water System

Abstract Use of recirculating-water systems risks transfer of hormones from one group of fish within the system to another group of fish within the same system. With this risk in mind, we conducted an experiment to determine if testosterone injections (1 mg/fish) into a group (N = 40) of rainbow trout (Oncorhynchus mykiss) would result in detectable levels of testosterone in the water and in the plasma of noninjected fish (N = 40) within the same recirculating-water system. Testosterone peaked in the water of the tank containing testosterone-injected fish 2 h after injection, and 4–6 h after injection in the water of the adjacent in-line tank containing saline-injected fish. Plasma-testosterone levels were significantly elevated (P < 0.05) in the fish not injected with testosterone when compared to controls in a separate system. We conclude that fish-to-fish transfer of testosterone can occur in a recirculating-water system. Caution should be exercised when designing experiments for exogenous hormone admi...