HEMATOLOGICAL RESPONSES OF RAINBOW TROUT TO CHEMICAL SEDATION USING TRICAINE, EUGENOL, AND METOMIDATE

Fish sedatives are used by fisheries professionals during routine transport and handling of fish to minimize stress, however sedation itself can induce departures from resting physiology. The present study was conducted to assess the hematological responses of rainbow trout following sedation with tricaine methanesulfonate (MS-222), eugenol, or metomidate hydrochloride.

Twelve rainbow trout (26.2 g) were group sedated then placed in a recovery tank. Three fish per sedative were bled at 0 minutes, 30 minutes, 4 hours, and 24 hours post sedation. Control fish were handled similarly but were not sedated. Each treatment was conducted in triplicate; three fish from the reference population were used for baseline. Whole blood was analyzed for pH, PCO₂, HCO₃, TCO₂, PO₂, and lactate using CG4+ i-STAT cartridges and hematocrit, hemoglobin, glucose, chloride, sodium, and potassium using 6+ i-STAT cartridges. Remaining blood was centrifuged and plasma stored at -80 °C for cortisol analysis.

While no significant treatment effects were found, time effects were found in all hematological responses (P<0.05, PO₂: P<0.1). Interaction effects were also observed: PCO₂ was higher in MS-222 fish (P<0.05) and control fish (P<0.1) at 0.5-hr post sedation than metomidate fish (Figure 1). PCO₂ was also higher in eugenol fish (P<0.1) at 0-hr post sedation than metomidate fish. PO₂ was lower in MS-222 fish (P<0.1) at 0.5-hr post sedation than metomidate fish and lower in eugenol fish (P<0.1) at 24-hr post sedation than fish sedated with MS-222 (Figure 2).

Hematological data seemed consistent with the generalized stress response and suggest minimal differences between handled and sedated rainbow trout exposed to a mild stress event.