Lotek has introduced a "field-proven" biotelemetry system designed to obtain, transmit and record the electromyograms (EMGs) produced in muscle activity of free-swimming fish as quantitative indicators of overall fish activity both in the laboratory and the field. EMGs are transmitted as radio pulses; the intensity of muscular activity determines the interval between pulses. The transmitter package also contains temperature sensors that allow it to transmit fish temperature after every thirty-second pulse. Transmitted EMG and temperature pulses are detected, measured and stored by a single portable receiver/datalogger (SRX 400).
Background
Active swimming at different speeds is only one element in determining
the intensity of fish muscule activity and its underlying energy costs.
Starts from rest and changes in speed, direction or position, all of
which require acceleration or deceleration of fish mass, can be much
more energy demanding than steady-state swimming. These sometimes scarcely
noticeable changes of pace and direction that many fish make constantly,
can be highly significant in the total movement energetics of daily
activity regimes.
The EMG/TEMPERATURE biotelemetry system developed at Lotek can detect, transmit and evaluate such movements. Electromyograms (EMGs) are records of bioelectric potentials that are strongly correlated with the strength and duration of muscle contractions. Indeed, EMG values averaged over time can be used directly as quantitative indicators of the intensity of fish activity. EMG values can be "calibrated" in terms of fish oxygen consumptions measured over periods of spontaneous activity or over the same times in swims of selected speeds and durations. This in turn allows investigators to obtain quantitative estimates of the metabolic costs of activity by wild fish under field conditions.
The System
The system is designed for extended duration studies of the swimming
activity, behaviours patterns and/or estimates of the energetics of
activity in free-swimming fish both in the laboratory and in the field.
All components of the system are compact, portable and rugged to facilitate
use in the field. Removal of the system from the field is not necessary
for retrieval of data. Data may be stored and averaged as required for
particular applications and later transferred via RS-232 communication
port to a laptop or remote computer via telephone, cellular or satellite
link.
The system consists of:
- One or more transmitters
- An SRX_400 datalogger/receiver with EMG/temperature firmware
- Antennas appropriate to the experiment/location
- File management and communication support software
Transmitters: The implantable transmitter (16.2 mm x 53 mm) contains an instrumentation amplifier for low voltage, high impedance EMG signals from the Teflon coated, stainless-steel electrodes embedded in the muscle. Signals are processed through an integrator and a radio pulse is transmitted when a predetermined threshold value is reached. Increasing muscle activity (EMG production) results in a corresponding decrease in the interval between successive radio pulses. Fish body temperature, measured via a thermistor (temperature sensor) and transposed into a time interval, is transmitted after every thirty second pulse. Operating life is 3 to 4 months, depending on fish activity.
Receiver: The SRX_400 compact, field portable receiver/datalogger provides real time processing and storage of EMG/temperature signals. The receiver's firmware is designed to poll a number of independently calibrated sensors transmitting on different frequencies. EMG data is presented at the beginning of the first line of the receiver display, formatted as a dimensionless number (actually a pulse interval in tenths of a millisecond) representing average muscle activity over the interval (on the order of one second).Temperature in degrees, with 0.1 degree C resolution, and corresponding temperature pulse width, occupies the rest of the line. Calculation of mean and standard deviation on all received EMG data and their values are reported in formatted dumps. Users may specify the minimum number of EMG pulses the program will try to collect for each transmitter before creating a record. Users may also select a start and stop time for a daily activity window, outside of which no signals are recognized or data recorded. Data stored in long-term memory may be transferred to an external device via the RS232 port.
Lotek's EMG/temperature system has numerous advantages over current technology. Some of its features are:
Compact data
acquisition and storage receiver
The SRX_400 with its modular compiled C-language operating system, provides
real-time signal processing and almost 600KB data storage, which is
equivalent to 38,000 EMG/Temperature measurements. An additional 512
KB of data memory is available as an option.
Signal/Signature
recognition
A routine referred to as "WINDOWS" in the firmware provides
access to two sets of user configurable pulse interval boundary values
("Temperature" and "EMG")used to discriminate temperature
and EMG values from noise.
User selectable
calibration method
The user can enter temperature calibration data for each transmitter
and can select from three calibration methods which use polynomial interpolators.
Sampling flexibility
The user can set the minimum number of EMG pulses the program will try
to collect before creating a record. The user can also define a start/stop
time for a daily activity window, outside of which no signals are recognized.
The same daily pattern of sampling is repeated until the window is reprogrammed.
Unattended field
operation
The system may be deployed in the field for extended periods through
the use of an external 12 volt power supply. Data may be dumped to a
portable computer in the field. Placing a Hayes-compatible modem at
the receiver and at a desktop computer enables the researcher to remotely
control or interrogate the receiver via cellular phone, or other communication
link, even via satellite, if that is required.
- Potential
Applications
Catch release studies - Fish activity and energy expenditures before, during and after catch and release can be more accurately assessed.
- Effects of pollutants on fish
- Growth and activity of fish are undoubtedly affected by pollutants (heavy metals, pesticides, heat effluents). The system would allow location and comparison of fish activity levels and, if required, energetics over a range of pollution levels.
- Effectiveness of fish passage structures
- Assessing the response of fish to different designs for fish passage structures can be greatly enhanced through the use of EMG to monitor actual energy expenditures as flow rates and structure designs are manipulated.
- Studies of growth and activity
- Growth and activity (as energy budget components) would appear useful for various predatory species occupying one body of water and drawing on the food stock (competition for resources) or in computing the energy costs of any migration.
- Activity changes associated with spawning
- EMG biotelemetry
provides a technique to determine precise location and timing of spawning,
as well as the sort of activity change (greater or less) associated
with the spawning act.
References
Further information regarding surgical procedures, placement of transmitter,
operations in the laboratory and the field can be found in:
Weatherley, A.H., Rogers, S.C., Pincock, D.G. & Patch, D.G. (1982). Oxygen consumption of active rainbow trout, Salmo gairdneri Richardson, derived from electromyograms obtained by radiotelemetry. J. Fish Biol. 20, 479-489.
Kaseloo, P.A., Weatherley, A.H., Lotimer, J.S. & Farina, M.D. (1991). A biotelemetry system for transmission of electromyograms in fish as indicators of physical activity. J. Fish Biol.
McKinley, R.S. (1991). Measurements of activity and oxygen consumption for adult lake sturgeon in the wild with radio transmitted EMG signals. Ontario Hydro Research Division. Report CB91-1-K
Thorstad, E.B., Okland, F., FInstad B. & McKinley, R.S. (1998). Development and use of EMG telemetry transmitters recording fish muscle activity. Proceedings of the Nordic Conference on Fish Passage.
Okland, F., Thorstad, E.B., Finstad, B. & McKinley, R.S. (1998). EMG radio transmitters - a new method to record activity, swimming speed and migratory costs in upstream migrating salmonids in situ. Proceedings of the Nordic Conference on Fish Passage.
