1. Territoriality and Space Defense

• Some fish species are naturally territorial and claim a specific area.

• They don’t allow other fish to approach and respond by chasing them away.

• This is especially common in male cichlid species.

• In small tanks, sharing territory becomes more difficult, which increases aggression.

1. Breeding Behaviors

• During breeding season, male fish may chase away other males to attract females.

• Females may also become aggressive to protect their eggs.

• Dominant behavior often increases during spawning or when guarding fry.

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1. Intra- or Inter-Species Competition

• Multiple males of the same species may chase each other to establish dominance.

• Hierarchy struggles can occur between fish of the same species but of different ages or sizes.

• Different species may also show similar behaviors, leading to aggression-based incompatibility.

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1. Stress, Overcrowding, and Limited Space

• Overcrowded tanks cause space shortages, leading to stressed fish.

• Stressed fish often become restless and aggressive.

• Lack of hiding places increases chasing behavior.

• Incorrect water parameters (temperature, pH, etc.) may also trigger behavioral issues.

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1. Wrong Species Selection

• Mixing peaceful species with aggressive ones creates imbalance.

• Some species prefer solitude and may become aggressive in groups.

• Fast-swimming fish may disturb slower species.

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1. Preventing Chasing Behavior

• Keep a number of fish appropriate to tank capacity.

• Provide plenty of hiding spaces (plants, caves, decorations).

• If multiple males of the same species are kept, increase the number of females.

• Keep compatible species together and separate aggressive ones.

• Relocate particularly aggressive fish to a separate tank if necessary.

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Conclusion
Fish chasing each other is not always a sign of serious aggression; however, if it becomes constant, it may lead to stress, injury, and even death. Understanding the reasons behind this behavior and taking proper precautions is essential to maintaining a peaceful and healthy aquarium environment.