Can fish get bored? Not in the way humans experience the emotion, but scientific evidence suggests they suffer from under-stimulation and monotony. Since we cannot ask fish about their feelings, researchers observe their behavior. In barren environments, their actions clearly indicate a welfare issue.
Defining Boredom in Animal Science
Because we cannot directly measure a fish’s subjective experience, researchers substitute the human concept of “boredom” with the measurable state of a “negative affective state resulting from low environmental stimulation.” This framework focuses on what the animal is lacking and how that deficit manifests behaviorally. In a stimulus-poor environment, an animal with a high need for cognitive input is unable to perform its full, natural behavioral repertoire.
Under-stimulation is a chronic condition caused by a lack of choice, novelty, or challenge. This drives the animal to seek out any form of stimulation. The resulting negative state is characterized by a motivation for general stimulation, which can be identified through behavioral tests where animals are willing to “work” for a change in their environment.
Cognitive Capabilities and Sentience in Fish
The idea that fish can be under-stimulated is rooted in their cognitive abilities and advanced learning capacity. Fish possess long-term memory, allowing them to recall migration routes, recognize individuals in their social groups, and remember the location of food sources. Studies show fish are capable of complex mental representation, such as spatial learning, where they acquire a map of their environment.
Some species exhibit problem-solving behaviors and can demonstrate numerical competence by distinguishing between different quantities. These complex cognitive processes indicate a need for sensory and intellectual input to remain active and engaged. When an environment fails to provide the complexity required to exercise these innate abilities, the fish’s unused capacity leads to monotony.
Observable Signs of Under-Stimulation
The most telling sign that a fish is suffering from a monotonous environment is the development of abnormal, repetitive behaviors known as stereotypies. These are fixed, compulsive actions that serve no apparent function and are rarely seen in the animal’s natural habitat. For the home aquarist, these behaviors are the most practical indicator of poor welfare related to under-stimulation.
The most common example is “glass surfing” or pacing, where a fish swims frantically and repeatedly up and down the tank glass in a fixed pattern. Other examples include swimming continuously in a tight circle, or repetitively rubbing one flank on the substrate or a tank surface, often referred to as flashing. Under-stimulation can also manifest as the opposite extreme, such as extreme lethargy, constant hiding, or a complete lack of exploratory behavior. When these fixed patterns of behavior become established, they suggest that the fish is attempting to cope with the frustration of an unfulfilling existence.
Providing Environmental Enrichment
Addressing under-stimulation requires introducing complexity and novelty into the fish’s habitat, a practice known as environmental enrichment. Enrichment should align with the species’ natural behaviors, such as providing social input for schooling species or ample substrate for bottom-dwelling fish to forage. Physical enrichment can involve frequently changing the arrangement of tank decor, introducing new elements like driftwood or live plants, or adding novel objects for exploration. Dietary enrichment stimulates natural foraging instincts by varying the feeding schedule, scattering food, or using slow-release puzzle feeders. Sensory enrichment might include adding different colors of background or introducing a gentle, variable water flow. By providing opportunities for choice and challenging a fish’s cognitive abilities, the environment can be transformed into a stimulating habitat.