Description

The Salmon Y-Maze is used to study the chemosensory behaviors of the salmon fish. The maze is an adaptation of the conventional Y-Maze which is often used in the evaluation of cognitive behaviors of rodents. Similar to the rodent maze, the Salmon Y-Maze also provides the subjects with two choices. The maze choice arms allow the creation of different investigatory conditions to evaluate behaviors that span from migratory to chemical disturbances.

Documentation

Introduction

Olfactory imprinting plays a critical role in the spawning behaviors of the salmon fish. Imprinting of the natal water olfactory cues has been observed to take place during smoltification (Bett, Hinch, Dittman, & Yun, 2016). These cues serve as a guide to spawning grounds. Chemical imprinting also contributes to homing behaviors and conspecific attraction. Investigations using the Y-Maze enable observation of the effects of olfactory imprinting and associated parameters under various experimental conditions.

The Salmon Y-Maze is a rectangular tank that has a start area and two choice arms created using a partition. The choice arms have provisions to create a downstream flow of water. Investigations often use a peristaltic pump to create different concentrations of solutions for the choice arms. Other similar apparatuses used in the behavioral assessment of fish, including cognition and memory assessment, include the Zebrafish Y-maze, the Y Maze Flow Modification and the Zebrafish Bifurcating T-Maze.

Apparatus and Equipment

The Salmon Y-maze is constructed of plywood, and its interior is sealed with fish-safe liquid rubber. The Y-maze is a rectangular chamber having a length of 370 cm, width 120 cm, and height 55 cm. A 250 cm partition made of plywood divides the upstream end into two equal parts, each constituting one choice arm in the chamber. A guillotine gate is fitted between the two halves of the chamber to control the movement of Salmon during the experiment. The peristaltic pumps help in maintaining the required rate of water and test solution entering the choice chambers.

Training Protocol

Clean all apparatus and equipment thoroughly prior to use. Conduct the experiment in a controlled environment. Adjust the lighting as per the photoperiod of the natural environment of Salmon. An external tracking and recording systems such as Nolde’s Ethovision XT can be used with the Y-maze for recording the fish activity.

It is important to drain and refill the water in Y-maze between trials to curtail the chances of any chemical cues from interfering with the succeeding trials. Ensure that control and test solutions must not mix with each other using a dye test.

Testing Procedure

Pump the stock solution in one arm of Y-maze using peristaltic pump till the final concentration of the test solution is attained. Introduce water in the other arm at the same rate. Start the trial by transferring subject to the downstream end of the Y-maze. Limit the subject to the start chamber using the gate for 20 minutes to allow acclimation to the apparatus. On completion of the acclimation process detach the plastic gate and allow the fish to move freely. Perform visual monitoring of the fish behavior for 30 minutes. Alter the arm containing test solution daily so that an equal number of trials can be conducted in both arms.

Investigation of olfactory imprinting in alevin stage

Bett et al. (2016) investigated the possibility of olfactory imprinting in Pink Salmon alevins prior to the full absorption of the yolk sac and emergence. Subjects were divided into two treatment groups during the alevin stage; one group was reared as controls in control water while the other group was reared in water containing 10^-7 M phenethyl alcohol (PEA). The matured subjects were then evaluated in the Y-Maze task wherein one arm had 10^-7 M PEA solution water, and the other had control water. It was observed that the PEA exposed group spent more time in the PEA arm and also more frequently crossed through the stream of water flowing in this arm.

Responses of Pacific salmon to chemical disturbance cues

Bett, Hinch, and Yun (2016) conducted experiments for studying the avoidance response of wild salmon to disturbance cues produced by disturbed conspecifics. They also investigated the role of cortisol as a disturbance cue. Sockeye and Pink salmon were used as subjects. The subject fish was treated with a specific handling protocol same as that of disturbed conspecifics before entering the Y-maze. The source fish was divided into two treatment groups disturbed and control. One arm of Y-maze contained disturbed conspecifics odor whereas, the other one contained control conspecifics odor. In the other experiment, cortisol containing water is pumped in one arm of Y-maze acting as a disturbed conspecific. Results indicate that sockeye salmon showed avoidance to the disturbance cues produced by disturbed group whereas, pink salmon did not. In the other experiment, no significant behavioral response was observed against cortisol indicating it isn’t a disturbance cue for both salmon species.

Role of amino acids in natal stream recognition

Yamamoto and Ueda (2009) studied the role of amino acids in the natal stream as an influencing factor for homing behaviors. The subjects were four-year-old adult male salmon, treated in natural lake water. For the experiment, combinations of control (lake) water and three artificial streams water using amino acids were used. The Y-maze allowed the scientists to compare the fish response towards the natural water and artificially prepared water, each present in one of the choice arms. The results showed that chum fish recognized natal stream water and were affected by the change of multiple amino acids in the water. On the contrary, alteration of single amino acid did not affect the fish response.

Data Analysis

The following parameters can be observed using the Salmon Y-maze are:

• Time spent in each arm of Y-maze
• Number of line crossings

• Number of U-turns
• Distance covered
• Number of surfacing

Strengths & Limitations

Strengths

The Salmon Y-maze is easy to use and has a simple assembly. Due to its simplicity, the apparatus provides easily reproducible results. The test procedures performed in the Y-maze take less time and need minimum training of the subjects. The Salmon Y-maze can be effectively used in investigating alternative embryonic olfactory imprinting, homing behaviors, and factors affecting migratory and reproductive behaviors.

Limitations

The water used in Y-maze needs to be changed during the trial to prevent lingering chemosensory cues from affecting the fish behavior. The results obtained using the Y-maze are highly dependent upon the conditions in which the subject has been reared prior to entering the maze. Any change in water composition and natal water can also produce variation in the behavior of fish during the experiment. The experimental conditions including photosensitivity, feed and chemical composition of the solution must be keenly monitored during the trial.

Summary and Key Points

• Salmon Y-maze is used to study behavioral responses resulting from olfactory imprinting.
• Y-maze successfully produces results with all embryonic stages of salmon fish subjects.
• The construction and assembly of the Y-maze apparatus are easy and adaptable.
• The results obtained by using Y-maze with different varieties of salmon fish are extremely valuable for practical applications such as fish reproduction and population growth.
• To obtain accurate results, it is very important that water used during trials in Y-maze must retain its original composition and characteristics.

References

Bett, N. N., Hinch, S. G., Dittman, A. H., & Yun, S. S. (2016). Evidence of Olfactory Imprinting at an Early Life Stage in Pink Salmon (Oncorhynchus gorbuscha). Nature, 36393(6), 1-6. doi: 10.1038/srep36393

Bett, N. N, Hinch, S. G., & Yun, S. S. (2016). Behavioral responses of Pacific salmon to chemical disturbance cues. Behavioural Processes, 132(1), 76-84. doi: 10.1016/j.beproc.2016.10.001.

Yamamoto, Y., & Ueda, H. (2009). Behavioral Responses by Migratory Chum Salmon to Amino Acids in Natal Stream Water. Zoological Science, 26(11), 778-782. doi: 10.2108/zsj.26.778.