Introduction
Often times, electric fish utilize electrical signals to sense how the environment changes its signal. The signal is often known as electrolocation (items in the environment alter the electrical field) or electrocommunication (using electric abilities to signal to other fish). To emit these signals, the Glass Knifefish has specialized electrolytes near its tail comprising its electric organ. The electrolytes within the Glass Knife’s tail produce an almost continuous electric release known as the electric organ discharge (Assad, 1998). One problem the Glass Knifefish often faces is when two electric fish are close together, they can jam their signals if the fish continue using the same frequency as the other. After the fish meet, one fish will often change to a lower frequency while the other may change to a higher frequency (Heiligenberg, 1996). The result of this change is known as the jamming avoidance response (JAR). The JAR permits these fish to avoid other organisms by emitting these signals through electrolocation, thus providing a natural response that can be used to study frequency discrimination. The hypothesis of the following lab report is that if the just noticeable difference (jnd) is around +20 hertz (Hz), the Knifefish will trigger not JAR at +0 Hz, +10 Hz, and +40Hz. The concept of jnd comes from the early work of in the area of classical psychophysics carried out in the mid-nineteenth century. The work conducted by Weber, a German physiologist, focused on tactile stimulation and the determination of sensory thresholds (Stern, 2010). Ultimately, the following lab report discusses how similar the conspecific frequency must be to stimulate a JAR and determine the jnd in the Glass Knifefish.
Materials and Methods
A 10 gallon aquarium was utilized to hold a Glass Knifefish. To ensure the fish would stay relatively still, the Glass Knife was placed inside a home tube. Copper recording electrodes were placed insides the aquarium and connected to the audio amplifier and speaker. The electrodes were oriented so the bottom 3-4 centimeters of one was placed close to the head of the fish while the other electrode was placed similarly, but toward the tail. The speaker was turned on to listen to the frequency emitted from the fish. LabChart 8 was set up and connected to the PowerLab oscilloscope emulator to aid in visualizing the fish’s wave form and to play an artificial electrical signal to the fish. This set-up provided real time imaging of the results and the waveforms produced by the frequencies emitted from the fish as a response to the artificial signals created by the stimulator.
The actual EOD waveform of the fish was obtained and recorded using the LabChart program. After the EOD of the fish was monitored and measured, pre-determined frequencies of 0 Hz, +10 Hz, +20 Hz, and +40 Hz were emitted for approximately 30 seconds through the utilization of an apparatus called the “stimulator” that was built into LabChart 8. These frequencies were tested in two trials and were randomized to eliminate any biases or environmental factors. Between each trial, the Ghost Knife was rested for 5 minutes to allow the subject to recover to its normal EOD frequency and to ensure the best signals were emitted from the fish after each stimulation. After the 8 trials were completed, the data was observed to find the range in frequency in which the fish emitted the largest change in frequency as a response to the stimulation. Two more frequencies were then selected to be examined between the decided range of frequencies in order to determine the jnd.
Results
Graph 1: The graph above provides a detailed view of the change in stimulus frequency versus the change in response to the emitted frequencies of 0 Hz, +10 Hz, +20 Hz, and +40 Hz. The jnd was shown to be between +10 Hz and +20 Hz through the observation of the standard error bars.
Figure 1: Trial 1 at 14 Hertz shows there was a change in response frequency of 2.4 Hertz from the fish. This is shown by a change in tank frequency because the Knifefish changed its frequency, altering the frequency within the tank.
Figure 2: Trial 2 at 14 Hertz shows there was a change in response frequency of 2.5 Hertz from the fish. This is shown by a change in tank frequency because the Knifefish changed its frequency, altering the frequency within the tank.
Figure 3: Trial 1 at 18 Hertz shows there was no change in response frequency from the fish.
Figure 4: Trial 2 at 18 Hertz shows there was no change in response frequency from the fish.
Mean Response
Δ +0 Mean Response
Δ +10 Mean Response
Δ +20 Mean Response
Δ +40
Standard Deviation 2.16 Hz 1.36 Hz 1.11 Hz 1.36 Hz
Standard Error 0.496 Hz 0.311 Hz 0.255 Hz 0.313 Hz
Table 1: Compilation of class data grouped by altered frequency; N = 19
Graph 2: Compilation of class data through a scatterplot graph to show the change in stimulus frequency versus the change in response of the fish. The just noticeable difference can be shown, again, between +10 Hz and +20 Hz through the observation of the standard error bars.
Through experimentation, the JAR was able to be shown in Figure 1 and Figure 2 because there is a noticeable change in tank frequency. The change highlights how the fish responded to the change in frequency from stimulation and is shown by the negative slope in Figure 2. Graph 1 and Graph 2 both showed similar results because the jnd fell within a comparable range of data points. The jnd was able to be found on these graphs by finding where the standard error bars do not intersect. Placement of these standard error bars allowed experimentation to find a more precise frequency range of the jnd.
Discussion
The jnd was observed to be between +10 Hz and +20 Hz. 14 Hz and 18 Hz were chosen because these frequencies were relatively close to each other while also being close to the minimum and maximum ends of the determined range. The compilated class data supports the reasoning behind testing 14 Hz and 18 Hz because the data showed that the jnd was between +10 Hz and +20 Hz of the EOD. Ultimately, the data supported that the JAR would be triggered at approximately +14 Hz. These results are important because JAR has been known to be used by fish in instances other than avoiding other fish. Brown-Ghost Knifefish have been known to establish supremacy over other members by emitting EOD frequencies. Fish with the highest EOD established dominance over other fishes. This knowledge opened a door in synthetic biology. From the knowledge obtained from examining JAR, muscles in other vertebrates or invertebrates could be influenced to create electrocytes for producing electrical power in human organs such as a heart, brain, spinal cord, etc (Assad, 2016). Investigating further into how JAR may influence other organs such as the heart could prove to be rather useful because it could allow doctors to utilize pacemakers to their full potential for patients. Discovering where a patient’s jnd may help a pacemaker work more effectively resulting in an overall better quality of life.
Precision is important in experiments in order to ensure they are carried out gracefully with intentions to find truthful results. The experiment was fulfilled rather precisely as the standard errors only ranged from 0.255 – 0.496 Hz. Error likely derived from noise emitting outside of the tank, people insisted on chatting amongst themselves. The placement of the electrodes may have also played a role in the reliability of the experiment because the cords were often bumped into which may have caused false readings. To improve these errors and to carry out a more reliable experiment in the future, it would be wise to ensure the surrounding area of the experiment is absolutely silent and to place the electrode cords away from computers to avoid false readings.
The results do not support the hypothesis because the jnd was not at +20 Hz, the jnd was found to be within a range of +10 Hz and +20 Hz. Although the hypothesis was not completely supported, the results from the experiment show the Glass Knifefish did not trigger JAR at frequencies of +0 Hz and +40 Hz. This information was supported in the data because the mean response of +10 Hz and +20 Hz had standard deviations of 1.36 Hz and 1.11 Hz with standard errors of 0.311 and 0.255 Hz, respectively. Standard error bars were utilized to discover in which the range of jnd was within because they give information about replication (Cumming, 2010). With the finding from the experiment, it was able to be concluded that the jnd falls within +10 Hz and +20 Hz meaning the Glass Knifefish will emit its JAR between this range.