Aggression: Bettas are known to be territorial and aggressive fish, especially toward other fish with similar colors or long fins. Sucker fishes, such as the common pleco, can grow quite large and may compete with bettas for space and food. This can lead to stress and aggression from the betta, which can negatively impact both fish's health.
Fin nipping: Bettas are also known fin nippers, meaning they may nip the delicate fins of other fish. Sucker fishes have long, flowing fins that are particularly vulnerable to nipping, which can cause injury, infection, and stress.
Competition for food: Sucker fishes are bottom-feeders, meaning they scavenge for food on the bottom of the tank. Bettas are typically surface feeders, meaning they prefer to eat food that floats at the top of the water. Having a bottom-feeder in the tank can make it difficult for the betta to get enough food, leading to malnutrition and health issues.
Water quality: Sucker fishes can produce a significant amount of waste, which can impact the water quality in the tank. This can be a problem for bettas, as they are sensitive to changes in water conditions and may become stressed or ill if the water quality is not kept pristine.
For these reasons, it's best to keep bettas and sucker fishes in separate tanks or, if you have a very large tank, ensure there is ample space and hiding spots to minimize interaction and potential conflict.