Semi-Aggressive fish are fish that can do well in a community tank but may be bothersome to smaller, less boisterous fish. I also included fish that do well when in a community tank with only one of their kind. Red Tailed Shark and the Rainbow Shark are examples of this type of fish. Tiger Barbs could be classified as semi-aggressive fish because of their fin nipping nature.
"Aggressive" can mean different things. Some fish like cichlids are aggressive to their own species regularly, during spawning, etc., and this is normal and not a cause for concern if their aquarium is properly designed for them. However, a fish that is aggressive to other species in the tank can be a problem.
Fish that are under continual threat from aggressive fish will not be healthy. Aggression or bullying towards a fish causes stress, and stress always leads to long-term health issues and disease. Fish that regularly display aggression towards other species should not be housed in the same aquarium.
A pair of dwarf cichlids in a community tank with shoals of tetras will not be problematic even though they will display some level of aggressive behaviour from time to time. By contrast, a group of small tetras like Aphyocharax paraguayensis or a few Tiger barbs will terrorize other fish like neons and similar, even in large aquaria. I speak from personal experience.
View some semi aggressive tropical fish:
Zebra Danios
Clown Loach
Tiger Barbs
Cherry Barbs
Red Tailed Black Shark
Serpae Tetra
Aurora Cichlid
Big-Finned Bristlenose Pleco
Black Acara, Port Acara
Black-Ghost Knife Fish
Blue Acara
Blue Gourami, Three Spot Gourami
Clarias Catfish, or Walking Catfish
Dragon Fish.
Electric Yellow Cichlid.
Fire Eel
Firemouth Cichlid.
Keyhole Cichlid
Krib
Leopard Bushfish
Paradise Fish
Rainbow Shark
Red-Tailed Black Shark
Tiger Barb
