Energy allocations to xenobiotic transport and biotransformation reactions in rainbow trout (Oncorhynchus mykiss) during energy intake restriction.

Energy restrictions can down-regulate cellular defence mechanisms, or if maintained, result in energy trade-offs with other processes. Trout were fed full-rations (1.17% body-weight/day), half-rations (0.59% body-weight/day), or fasted for 9 weeks followed by re-feeding full-rations. Body-weight, liver somatic index, and P-glycoprotein (P-gp), Ethoxyresorufin-O-deethylase (EROD), and Glutathione-S-transferase (GST) activities were monitored to investigate their maintenance under limited resources. P-gp and EROD activities were maintained in ration-restricted (P-gp: 119±29 pg/min/mg cells, EROD: 0.58±0.17 nmol/min/mg protein) and fasted fish (P-gp: 120±14 pg/min/mg cells, EROD: 0.47±0.14 nmol/min/mg protein). GST activity was significantly attenuated (34%) within 6 weeks of fasting, but recoverable to baseline values after re-feeding. Significant reductions in condition indices of calorie-restricted (BW: 16%; LSI: 33%) and fasted trout (BW: 38%; LSI: 44%) suggest mobilization of body stores to support these systems. Condition indices and defence activities also varied over time, suggesting that water temperature change (range: 13-17°C) may modulate these parameters.