A question of temperature related differences in plasma oxolinic acid concentrations achieved in rainbow trout (Oncorhynchus mykiss) under laboratory conditions following multiple oral dosing

This work investigated the plasma oxolinic acid (OXA) concentrations achieved by multiple administrations of medicated feed to laboratory held rainbow trout (Oncorhynchus mykiss) at 6 °C. These data were compared with previously published data obtained with trout held at 12 °C. Both sets of fish were administered oxolinic acid at 50 mg/kg at 1% body weight on six occasions during a 9-day period and sampled 1 day after the last administration of medicated feed. The mean plasma OXA concentrations were 0.14±0.07 and 0.15±0.10 mg/l while the 80th percentiles were 0.09 and 0.08 mg/l, at 12 °C and 6 °C, respectively. The extent of fish to fish variation, measured as the percentage coefficient of variation (CV), were 47% and 66% at the two temperatures. These data indicate that temperature, over the range 6-12 °C is not a significant factor in determining plasma concentrations achieved following multiple oral administrations of medicated feed. It is argued that a single breakpoint MIC value could be applied to any therapeutic treatment performed within this temperature range.