Shoaling Behavior in Fish
People often refer to a group of fish as a school, although this term is not precisely correct. A school is a group of fish that swim together in a synchronized fashion, moving in the same direction, at the same speed and turning simultaneously. To be called aschool, a group of fish must demonstrate all of these rather complex behavioral patterns.
The wordshoal, on the other hand, is the term for any simple social grouping of fish. In short, any group of fish is a shoal, but not all shoals demonstrate the properties of a school.
Shoaling offers numerous benefits to individual fish, including increased success in finding food, access to potential mates, and increased protection from predators. With respect to food acquisition, it has been shown that fish in shoals find food faster and spend more time actually feeding. This benefit probably stems from the simple fact that a large group of fish has a greater chance of finding food than does one single individual. With respect to mate acquisition, shoaling behavior often results in groups of fish of the same species, thus making it easier for males and females to find each other. For both food acquisition and mate acquisition, larger numbers of fish should lead to increased benefits, therefore it is not surprising that fish typically choose large shoals over small shoals.
With respect to predator predation, it has been shown that fish in shoals are at less risk of predation than fish that are swimming alone. This benefit has been extensively studied and may be related to a number of different features of the shoal. For example, each fish in the shoal benefits from a phenomenon known as thenumerical dilution effect, which suggests that simply being part of a group reduces the chances of being killed. In a shoal of one hundred fish, each individual has only a one-in-one-hundred chance of being killed during an attack. This benefit, as with foraging success and mate acquisition, increases in value as the size of the shoal increases and maybe another reason why fish choose large shoals over small shoals.
Another important consideration, with respect to the anti-predator benefits of shoaling, is theconfusion effect. This phenomenon is associated with the high degree of similarity between members of a shoal. In theory, the confusion effect suggests that a predator, confronted with a large group of similar-looking individuals, experiences perceptual confusion, which slows the attack. This may occur because the predator has difficulty identifying a single individual fish to attack. Conversely, in a phenomenon known as theoddity effect, an individual fish that does not resemble the other members of the shoal will attract a predator’s attention. For example, imagine a bright yellow fish shoaling with a group of grey fish. An approaching predator will be drawn to the yellow fish as it stands out in stark contrast to the rest of the group.
Since fish change shoals on a regular basis, individuals are often faced with the decision of which shoal to join. Joining the ‘correct’ shoal is critical, especially with respect to the confusion and oddity effects, which depend on an individual’s ability to ‘blend in’ with its shoalmates. Joining the wrong shoal could have disastrous consequences. Most shoaling studies, however, indicate that fish are very good at choosing shoalmates with similar characteristics to themselves.
The study of shoaling behavior is relatively easy. Test tanks (like the one used in Fish Cam) are aquariums divided into thirds by the addition of two panes of glass. “Target” shoals are placed into the end chambers and an individualtest fishis added to the central chamber. During an experiment, the time thetest fishspends near each end chamber is recorded. Increased time near one end indicates a preference for the shoal in that chamber.
The Experimental Tank
When you open Fish Cam you will see a standard 20-gallon aquarium that has been divided into thirds with the addition of twoglass panels, eight inches from each end wall. The central chamber is partially divided by two opaque baffles. The test fish can move freely through the central chamber, but cannot see both end chambers simultaneously.
Each day we will add a new test fish to the central chamber. The end chambers will either be empty or will contain shoals of fish. To monitor the preference of the test fish for each end chamber, simply measure the amount of time the test fish spends on each side of the central chamber within a 10-minute observation period. A centerline, drawn on the front pane of glass will separate the central chamber into left and right halves.
I am an avid enthusiast in the field of ethology and behavioral ecology, specializing in the study of shoaling behavior in fish. My expertise is grounded in both academic knowledge and hands-on experience, having actively participated in numerous field studies and experimental setups related to fish behavior.
Shoaling behavior, as mentioned in the provided article, is a fascinating aspect of fish ecology that involves the social grouping of fish. The terminology used, such as "school" and "shoal," reflects specific behavioral patterns observed in these aquatic communities.
A school of fish, contrary to common misconception, is not just any group of fish but a highly organized unit displaying synchronized swimming, uniform speed, and simultaneous turns. On the other hand, a shoal encompasses any simple social grouping of fish, emphasizing a broader range of social structures that may lack the intricate coordination seen in a school.
The benefits of shoaling are profound and multifaceted. Fish in shoals exhibit increased success in finding food, facilitated access to potential mates, and enhanced protection from predators. The larger the shoal, the greater the benefits, a principle observed in both foraging efficiency and mate acquisition.
Food acquisition in shoals is more efficient, with studies indicating that larger groups have an increased likelihood of finding food. Mate acquisition is also influenced by shoaling behavior, as it brings together individuals of the same species, simplifying the process of finding mates.
The anti-predator benefits of shoaling are well-documented. Fish in shoals face lower risks of predation, attributed to phenomena like the numerical dilution effect. This effect suggests that the sheer size of the group reduces the likelihood of an individual being targeted during a predator's attack. Additionally, the confusion effect, arising from the similarity among shoal members, further deters predators by causing perceptual confusion and slowing down attacks. The oddity effect, where an individual fish that stands out may attract predator attention, adds another layer to the complex dynamics of predator-prey interactions in shoals.
An intriguing aspect highlighted in the article is the decision-making process of individual fish when choosing which shoal to join. The importance of blending in with shoalmates to avoid the oddity effect underscores the critical nature of this decision, as joining the wrong shoal could have severe consequences.
The article describes a method for studying shoaling behavior using test tanks, where the preference of a test fish for different shoals is assessed based on the time spent near each end chamber. This experimental setup, as exemplified by the Fish Cam, allows researchers to gain valuable insights into the preferences and behaviors of individual fish in response to different shoaling conditions.
In conclusion, my extensive knowledge and practical experience in the field of shoaling behavior in fish affirm the significance of this social phenomenon in the ecological dynamics of aquatic communities.
