Physiological Effects of Recovery Period on Rainbow Trout

Many studies using fish telemetry have been conducted. When a telemetry transmitter is attached to fish, it is common to perform the surgery under anesthesia. The length of the recovery period between anesthesia / surgery and the release of fish varies. When conducting an experiment in a river, lake or marsh, fish are usually put in a recovery cage to watch over a weakening of fish and damage or detachment of the transmitters. However, there have been very few studies that investigated carefully recovery period after anesthesia and surgery, and there are many unclear points concerning the physiological effects of recovery period on fish.

In this study, rainbow trout, Oncorhynchus mykiss, were put in a swim chamber where they could freely swim in order to determine the time between the end of anesthesia/surgery and the recovery of their swimming ability.

The experiments were conducted between June and August 2010, using a total of 28 fish of both sexes in a swim tunnel under three different conditions: anesthesia only (anesthetic: FA100), anesthesia + surgery (making holes in the fishes’ bodies), and anesthesia + EMG transmitter (CEMG, Lotek Inc.).  The critical swimming speed (U_crit) was measured five times from 1 to 30 hours after anesthesia/surgery in order to analyze the changes in their swimming ability. The flow velocity was increased by 0.125 m s^-1 every 15 minutes, and the U_crit values were calculated by measuring the time until fish got stuck into the end of the tank.  In addition, muscle activity was analyzed using EMG transmitters, and the dissolved oxygen (DO) consumption was measured using a water quality meter.

No significant difference was found between fish with EMG transmitters and the other two groups indicating that fish recovered their swimming ability within one hour after anesthesia/surgery.  The average U_crit value did not decrease during recovery period regardless of the surgery method.  Although rainbow trout swam unsteadily at the time of the first U_crit trial, they showed efficient swimming behavior at the second and subsequent trials suggesting the possibility that they had a learning ability based on the EMG values. The measurement of DO consumption one hour after anesthesia revealed that the amount of oxygen consumed was equivalent to that in case of swimming at 0.75m s^-1. The results of the present study are considered to be useful to select the release time of fish to which telemetry transmitters have been attached.