The behaviour of pet fish decoded: 9 signs explained

Understanding the behaviour of pet fish can seem challenging, as unlike mammals they do not show obvious personalities or clear social cues. However, by observing their typical actions and body language, fishkeepers can better meet their aquatic pets' needs, ensuring a healthy and harmonious aquarium.

This guide decodes nine common behaviours often seen in community tanks, explaining what each might mean and how to respond. Whether you keep tropical, coldwater, or marine fish, these insights help you spot signs of wellbeing or issues like stress, overcrowding, or aggression.

Coming to the surface of the tank

Fish often swim near the water surface for different reasons. They might be looking for food, especially if they approach the top when you near the tank. Alternatively, fish may seek warmth if the water is too cold, gathering near the tank lid where lighting generates heat. Regularly check your tanks temperature to ensure it suits the species you keep to avoid discomfort.

Gulping air at the surface

If fish are gulping air at the surface, this usually signals low oxygen levels in the tank. Causes can include insufficient aeration, overcrowding, or poor water quality due to a dirty filter system. Promptly assess your tanks aeration and cleanliness, and consider upgrading filtration or reducing fish numbers to improve oxygen availability.

Recognition and taming

Pet fish can learn feeding times and may gather near where food appears at predictable intervals. Some species like Koi carp and Cichlids can become tame enough to hand-feed, responding to their keepers presence with less wariness. This behaviour builds a positive interaction that benefits both fish and owner.

Signs of stress

Signs your fish are stressed include hiding excessively, chasing or being chased, dull colours, and ragged fins or tails. Stress can arise from unstable tank conditions, frequent disturbances, unsuitable water temperatures, or incompatible tankmates. The most common causes are overcrowding and mixing predatory species with smaller fish. Address these issues promptly to improve your fish wellbeing.

Identify overcrowding

A beautiful tank full of lively fish can be deceiving if overcrowded. A good rule of thumb is to allow at least one gallon of water per inch of fish. Overcrowding causes stress, increases fighting, and strains filtration systems, resulting in poorer water quality. Regularly evaluate fish numbers and tank size to maintain a balanced environment that supports healthy behaviour.

Aggressive behaviour

Some fish species are naturally more territorial or aggressive. For example, the Angelfish can prey on smaller, peaceful fish like the Neon Tetra. When stocking your tank, research and combine species carefully, avoiding mixing large predatory fish with smaller or shy species. For example, only one male Siamese Fighting Fish should be kept per tank to prevent serious aggression.

Group mentality

Some fish are solitary while others are shoaling species needing company to thrive. Most Tetras require at least six individuals to express natural shoaling behaviour; isolation stresses them. Ensure your tank composition respects the social needs of species, providing a healthier, less stressful environment.

Eating and avoiding being eaten

Fish daily life revolves around getting enough food while avoiding predators. A well-planted tank with sufficient décor, including live or artificial plants and ornaments, creates hiding places for smaller or timid fish. This reduces stress from predation risk and supports a peaceful community.

Interpreting fish behaviour for better care

By observing their movements, postures, and interactions, fishkeepers can decode their fish needs and emotions. Fish communicate through body language such as fin position, swimming speed, and colour changes. Frequent hiding or erratic swimming indicates stress or poor conditions. Chemical signals also play a part but are less visible to owners. Creating a habitat mimicking natural conditions, maintaining optimal water quality, and carefully selecting compatible species enhances fish welfare and communication.

Understanding these behaviours lets you respond effectively to your fish needs, preventing health and stress issues and fostering a deeper connection with your aquatic pets.