It is most important to know and understand behaviour of your fish just like any other pet.

The way your fish acts and behaves gives you clear idea about the health and environment your fish is living in like maintenance of aquarium water and many more things. Some most common fish behaviours are explained as follows:


When fish are introduced to new aquarium, most fishes show hiding as their natural and most common behaviour.


Many fish are show agression as their natural behaviour and always defend their territorial space till death. Some fish are not compatible to fit and house in the same aquarium and therefore they are almost seen fighting with other fishes.

Swimming Erratically

Fish generally swims erratically while playing or exercising but a consistent act of play or exercise will mean a stage where your fish can be unhealthy because of  bad quality water.

Testing water quality will discover cause of fish behaviour of swimming erratically.


Tired and lethargic fish can be due to many factors. Most common reason is improper water temperature. If  water is too hot or too cold, your fish will be very inactive. Other causes may be overfeeding or improper water quality.

Sitting on the Bottom

Fish behaves normally when they are seen spending lots of time at the bottom of the tank and also often sleep at the bottom of their water tank. If your fish activity does not fit any of these reasons, it may be a signal of any disease.

A disease that is a cause of this behaviour is a swim bladder infection, which is a result of a poor diet or improper water quality.

Gasping for Air

Fish may seen gasping for air at top of the aquarium and it can be due to improper water quality or due to insufficient dissolved oxygen in the water. Testing your water and considering an aerator for your water tank will solve the problem.

Reproductive Behaviour

Gonadal hormones are responsible for the regulation of reproductive behaviour of male and  female teleosts. The beginning of reproductive behaviour depends upon the occurrence of ovulation and spermiation.

Teleosts display varied patterns of reproductive behaviour. One species form temporary pairs and release gametes freely into the water while other species prepare a nest site and defend its territory and also go through pair formation and mating ceremonies.

These activities are followed by care of the eggs and young involving one or both sexes. There are phases in the breeding cycle which describes beahaviors of fishes: prespawning, spawning, and postspawning behaviours of males and females fishes:

  • Prespawning behaviour of males includes nest building and territorial defense, activities that precedes the release of gametes by hours or days. These behaviours persist after castration.
  • Prespawning behaviour of females: In most vertebrate species female fish plays passive role in mating process. Because of this, hormonal regulation of female behaviour has received far less attention than that of the male. Female undergoes regular cycles in sexual receptivity and displays maximum responsiveness to male courtship in the few days following parturition. The female also produces a pheromone which attracts and excites males.
  • Spawning behaviour of males and females: during breeding season they spawn daily for several days or even weeks, the female depositing relatively few eggs at a time. Oxytocin has no effect on spawning in either male or female goldfish.
  • Postspawning behaviour of males and females: In the great majority of teleost species spawning is followed by a break-up of the temporary pair, and neither partner pays any further attention to the eggs while in other species spawning is followed by a period in which one or both sexes guard the eggs and young.
  • Agonistic behaviour – non reproductive aggressive behaviour are reproductive behaviour patterns which function in a non reproductive context and occurs in a variety of behavioural situations like defense of a territory or nest site, and as a component in courtship, but it is also involved in a variety of non reproductive roles, including intraspecific competition for food and non breeding space, and the maintenance of individual distance and dominance status. The agonistic behaviour observed resulted in the establishment of dominance relationships.

Ambisexual Fishes Reproductive Behaviour

Parrot fishes and wrasses are among ambisexual fishes in that they have two distinct patterns of spawning. In fact, group and pair spawning may even occur in the same species.

Social interactions may be of temporary or of long duration, including pair bonding. None of these seem to be peculiar or exclusive to ambisexual species but they bear some relation to the mode of egg dispersal or protection, regardless of sex inversion.

A frequent pattern of spawning behaviour among teleosts is the annual aggregation of males and females, often in distinct places and involving migrations to special locations where spawning itself occurs.

Sex Inversion Behavioural Aspects

Some species are first males and then females and certain others turn from females to males in the course of their life histories. The phenomenon is called sex inversion.

Sex inversion is unique to teleost fishes, certain species initially reach maturity as males and later turn into females while others are first females and become males thereafter.

Sex-inverting species exhibit prominent spawning migrations and aggregations which provide opportunity for commercial fisheries.

Their color phases and their spawning behaviour, that is, group or pair spawning, are functionally related to genetic constitution and endocrine states of individuals.

At the outset teleost fishes are the only group among vertebrates in which spontaneous sex inversion occur. This deviation from the usual reproductive pattern in vertebrates poses problems broadly related to genetics, developmental physiology, comparative ethology, and evolution.

Swimming Behaviour

Swimming, of larvae may differ somewhat from adults.Tail beat amplitude and tail beat frequency are continuously modulated in larvae whereas in adult fishes amplitude is modulated less frequently, except during accelerations.

Tail beat frequency is inversely proportional to length in fishes and consequently, the frequency in early larval stages can be quite high.

Feeding Behaviour

Several molecules stimulate both smell and taste organs, but behavioural responses to these stimuli can be very different.

In general, amino acids and related compounds are important in eliciting both neurophysiological and behavioural responses. Feeding behaviour has been divided into an appetitive and a consummatory phase.
  • consummatory phases of feeding behaviour: Taste guards are used in the intake of food, determines its palatability, and detects food poisons. Thus, it serves a role in the consummatory phases of feeding behaviour. The consummatory phase is subdivided into a bite or pick-up phase, a chew and test phase and swallow or ingest phase.
  • The appetitive phase: Smell is involved in various appetitive behaviours, including prey detection, social recognition, and home area recognition. It is divided into a detection phase in which many fish use chemical signals to detect and identify their food at a distance, but then use other senses to locate the source. The olfactory sense organ with its complex neuroanatomy appears to be used for the detection phase of feeding behaviour. Other phases are identification phase (alert) and a locating phase (search): of the three major phases in feeding behaviour, the greatest differences among animals are to be found in the locating phase.

Both appetitive and consummatory phases of feeding behaviour are subject to environmental and endocrine stimuli and specifically to hunger state.

Most fish, however, briefly chew their food, making it possible for internal taste to judge palatability. Some fish (“gulpers”) may not taste their food before ingestion; others (“mouth tasters”) use taste and texture to sort edible material from a mouthful of debris and mud.

Where there are two distinct senses of taste (catfish, carp), internal taste has a higher acceptance threshold than external taste .Thus, the consummatory phase nearly always involves taste.

Searching Behaviour

Food density requirements have been estimated from behavioural search models . These models in their simplest form require an estimate of ration, swimming speed, perceptive field, and feeding success with many other parameters added as complexity increases.

Vlymen’s model the larvae have no effect on food density and the model does not use a prey size dependent modulation of perceptive field and feeding success.

searching abilities increase markedly with growth, since speed, capture success rates, and perceptive distances are functions of length or age.

Search patterns in larval fishes are non random. Larval decrease their speed and change their turning probabilities when they enter a dense patch of food.

Protective Behaviours

There are a number of potentially useful strategies which a fish might adopt to gain protection against predators during the period of adjustment.

These include freezing, hiding, seeking the company of other fish, and counterattack. The other responses are much more typical. Yellow perch dive but will remain motionless at the bottom corners of a pail,

hardly a satisfactory hiding place. Bluegills, do not even seek the bottom but will stay in a corner with contact on each side of the head. A number of fish such as the flounders are able to bury themselves very quickly in sand.


[Revised and Updated for July, 2019]
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Written by Debra Hutchinson, founder of FishXperts