Recently, research has increased regarding fish antinociception. Antinociceptive drugs commonly used in teleosts, such as morphine, butorphanol, meloxicam and robenacoxib, are injectable formulations. However, injections involve repeated fish captures, which can result in stress and increased risk of trauma in patients suffering from chronic nociceptive conditions. Clinical use of oral meloxicam is hindered by a low bioavailability and a short half-life as described in China rockfish and rainbow trout. Thus, oral administration of opioids should be evaluated in fish as an alternative to injections. The objectives of this study are to determine pharmacokinetic parameters after oral administration of a single dose of tramadol HCl in brook trout (Salvelinus fontinalis) and to evaluate clinically detectable adverse effects in fish. Six healthy adult brook trout kept at 11°C, five males and one female, were gavage fed with a tramadol compounded suspension at 5 mg/kg once. Tramadol was administered via a 10-Fr red rubber tube in the stomach along with yellow-colored thiamine solution, and the cranial part of the body was maintained elevated for 30 seconds to prevent regurgitations. Blood samples were obtained from the ventral coccygeal vein initially and at 1h, 2h, 4h, 6h, 24h, 32h and 46h after drug administration. Sedation and swimming position were evaluated at each time point. Plasma concentrations of tramadol and its two main metabolites M1 (O-desmethyltramadol) and M2 (N-desmethyltramadol) were measured by high-performance liquid chromatography. Pharmacokinetic parameters and adverse effects will be presented. Future work includes a pharmacodynamic study to evaluate tramadol antinociception effect in trout.