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Mirror tests are frequently employed in investigations of confrontational behavior, particularly in research on aggression among fish, as they necessitate fewer participants and circumvent issues of pseudo-replication. Additionally, mirrors elicit a robust aggressive reaction from the subject without posing any risk to their safety. MazeEngineers provides a variety of mirror biting test models, reflecting the absence of a clear standard that has emerged from the existing literature.
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The Mirror Biting test serves as a valuable tool for delving into the intricacies of sociability among fish. Typically, sociability is assessed by monitoring the duration fish spend in close proximity to a stimulus. Mirror tests utilize mirrors as a surrogate for live stimuli, operating under the assumption that the subject interprets the reflection as another live conspecific. This approach theoretically enables better control over behavioral variability compared to live stimuli, facilitating standardized behavior and facilitating repeated measurements of individual subjects.
Sociability manifests in various degrees across numerous fish species, often observed through their tendency to form shoals. Shoaling offers several advantages, including heightened vigilance against predators, decreased individual predation risk, and enhanced efficiency in locating food sources. However, despite its benefits, shoaling comes with drawbacks such as increased resource competition and elevated risk of parasite transmission. Evolutionary biologists have long been intrigued by the concept of sociability, pondering the trade-offs fish must navigate concerning shoaling.
Cattelan’s mirror biting apparatus comprises a glass aquarium partitioned into three compartments by transparent plastic partitions. These partitions feature holes to facilitate visual and olfactory interaction between the focal and stimulus subjects. The smaller lateral compartments house the stimulus shoals/individuals, while the larger central compartment accommodates the focal subject. When conducting tests involving mirrors, one of the lateral sections replaces the partitioning plate with a one-way mirror.
Additional apparatus akin to the Mirror Biting (Cattelan) setup includes the Mirror Biting (Balzarini) and Mirror Biting (Elwood) configurations.
Before commencing the experiments, meticulously sanitize the apparatus. Then, fill the tank with a precise 14 cm depth of pristine water. It’s imperative to refresh both the stimulus shoal and the water within the experimental tank once every three trials. Ensure proper illumination of the lateral compartments of the tank. For meticulous tracking and recording, consider utilizing video and software solutions like Noldus EthoVision XT. Maintain the water temperature at ambient levels and dim the lights in the testing room throughout the experiment for consistency.To prevent any undue influence from prior interactions, isolate the focal subjects in individual holding tanks before and between tests, carefully shielding them from visual or olfactory cues of other fish. This precaution helps to minimize any potential biases stemming from previous encounters.
Introduce the focal subject into the central compartment, specifically in the no-choice area, granting it a minimum of two minutes for acclimatization to its surroundings. To mitigate any potential lateral bias, systematically alternate the positions of the shoals between the lateral chambers in successive trials. Dedicate a minimum observation period of 10 minutes to monitor the interactions of the focal subject. This approach ensures thorough assessment while minimizing any predispositions that may arise from consistent lateral placements of the stimulus shoals.
Exchange one of the partitions with a one-way mirror, ensuring to alternate its placement between the two sides to prevent any lateral bias. Subsequently, introduce the focal subject into the central compartment, specifically in the no-choice area, affording it a minimum of two minutes for environmental acclimatization. Dedicate a minimum observation period of 10 minutes to assess the interactions of the focal subject. This methodology fosters comprehensive evaluation while mitigating potential biases that may stem from consistent lateral positions of the mirror.
In a study conducted by Cattelan et al. (2017), female guppies underwent assessment in the Mirror Biting test to gauge their social preferences when presented with either an unfamiliar shoal or a mirror. Observations of the focal subjects’ positions across the three distinct areas, made at 12-second intervals throughout the 10-minute trial, revealed noteworthy findings. Notably, the subjects exhibited a pronounced preference for social stimuli (both the shoal and mirror) over the empty chamber. However, intriguingly, no discernible difference in the mean preference was observed between interaction with live conspecifics and the mirror. This suggests a complex interplay of social dynamics and self-recognition mechanisms worthy of further investigation.
In the study conducted by Cattelan et al. (2017), the Mirror Biting test was conducted with a single live conspecific instead of a shoal to evaluate whether a solitary individual would elicit comparable sociability scores to those induced by a mirror stimulus. Notably, the focal subject exhibited a heightened preference for the live conspecific over the mirror image. This finding underscores the robustness of the mirror biting test as a reliable tool for assessing sociability in fish, reaffirming its utility in behavioral research.
The following behaviors and parameters can be observed in the Mirror Biting test
Mirror tests have consistently proven to be a dependable metric for assessing fish behavior in social contexts, with their social behaviors exhibiting a positive correlation with shoaling tendencies. The flexibility of the mirror setup allows for its removal or addition as dictated by experimental requirements. Moreover, the utilization of two distinct protocols in the Mirror Biting test permits the introduction of varying degrees of novelty, providing researchers with nuanced insights into fish behavior.
When the mirror is introduced to a tank already occupied by fish, it tends to elicit heightened territorial behavior, adding depth to behavioral observations. The construction of the apparatus is straightforward, facilitating easy modifications tailored to the specific needs of individual investigations. The tank’s narrow design further enables the creation of diverse shoal densities, facilitating comprehensive evaluations of shoaling behaviors across varying experimental conditions.
While a correlation between mirror-directed behavior and sociability exists, it’s crucial to acknowledge the limitations of the mirror test as a method for understanding sociability. Some mirror-directed behaviors may stem from fear avoidance rather than true social interaction. Additionally, the mirror test fails to replicate the nuanced characteristics of a genuine conspecific stimulus, necessitating caution in interpreting results.
Furthermore, the clarity of the mirror image may be compromised when viewed from close proximity, potentially impacting the subject’s response. Moreover, the test deprives the subject of chemical cues vital in typical social interactions among fish when utilizing a mirror image stimulus.
The social personality types of both the subject and the stimulus conspecific significantly influence the outcomes. Anxious individuals, for instance, may not exhibit anticipated behaviors when introduced to a tank already containing a mirror. These considerations underscore the need for cautious interpretation and the importance of recognizing the multifaceted nature of fish behavior in experimental settings.
Cattelan S, Lucon-Xiccato T, Pilastro A, Griggio M (2017). Is the mirror test a valid measure of fish sociability? Animal Behaviour 127 (2017) 109-116
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