I know most members on here have smaller tanks and like smaller fish. So I thought I'd throw a list together of Mini Monster fish. Feel free to add any information about a species to my short description or any other Mini Monsters that you know of 
1. Exodon Tetras. Temperament: Aggressive, must be kept in a species tank only. They do best in large schools and should be fed meaty foods such as shrimp, tilapia, beef heart, etc. I wouldn't get any less than 10 per school. Minimum Tank Size: 30 Gallons.
2. Wimple Piranha. Same thing as Exodons but can be successfully kept with Plecos and do better than Exodons in smaller groups of at least 4. A great solution if you want to get red bellies and don't have a large enough tank. Minimum Tank Size: 55 Gallons
3. African Butterfly Fish Temperment: Peaceful yet will eat anything that can fit in its mouth. These fish must have a tight fitting lid, they are jumpers. Relatives to Arowanas and basically the smallest Arowana. Minimum Tank Size: 30 Gallons
4. Peacock Eel. Very peaceful fish yet can be very picky. Must be fed frozen or live foods such as blood worms, small pieces of shrimp or tilapia, earth worms, black worms, and live ghost shrimp. Will eat small fish and should not be kept with shrimp such as cherry or Ghosts if they aren't meant for feeders. Peacocks are a great solution to its larger counter parts the Fire Eel and Tire Track. They do best if given a cave to hide in, peaceful tank mates, and a sand or soft substrate. Minimum Tank Size: 30 Gallon Breeder
5. Silver Dollars. These fish can grow to a somewhat large size but they are a good solution if you like Red Bellied Pacu and don't have a large enough tank. They are peaceful fish that should be kept in schools and can go well with larger aggressive fish. They should not be kept with plants or they will eat them all. Minimum tank size: 55 Gallons
I will probably end up thinking of more later but this all I've got for now and I did all of this off the top of my head. Feel free to add pictures, max sizes, and more detailed descriptions.
1. Exodon Tetras. Temperament: Aggressive, must be kept in a species tank only. They do best in large schools and should be fed meaty foods such as shrimp, tilapia, beef heart, etc. I wouldn't get any less than 10 per school. Minimum Tank Size: 30 Gallons.
2. Wimple Piranha. Same thing as Exodons but can be successfully kept with Plecos and do better than Exodons in smaller groups of at least 4. A great solution if you want to get red bellies and don't have a large enough tank. Minimum Tank Size: 55 Gallons
3. African Butterfly Fish Temperment: Peaceful yet will eat anything that can fit in its mouth. These fish must have a tight fitting lid, they are jumpers. Relatives to Arowanas and basically the smallest Arowana. Minimum Tank Size: 30 Gallons
4. Peacock Eel. Very peaceful fish yet can be very picky. Must be fed frozen or live foods such as blood worms, small pieces of shrimp or tilapia, earth worms, black worms, and live ghost shrimp. Will eat small fish and should not be kept with shrimp such as cherry or Ghosts if they aren't meant for feeders. Peacocks are a great solution to its larger counter parts the Fire Eel and Tire Track. They do best if given a cave to hide in, peaceful tank mates, and a sand or soft substrate. Minimum Tank Size: 30 Gallon Breeder
5. Silver Dollars. These fish can grow to a somewhat large size but they are a good solution if you like Red Bellied Pacu and don't have a large enough tank. They are peaceful fish that should be kept in schools and can go well with larger aggressive fish. They should not be kept with plants or they will eat them all. Minimum tank size: 55 Gallons
I will probably end up thinking of more later but this all I've got for now and I did all of this off the top of my head. Feel free to add pictures, max sizes, and more detailed descriptions.
