Yes, a plecostomus needs a heater. Like other tropical fish, a plecostomus needs warm temperatures to thrive, around 74° F and 80° F (23° C and 26.5° C). Suboptimal water temperatures can lead to growth stunts, a weakened immune system, stress, illnesses, and even death.
Even if you place your pleco’s tank in a warm area, the water temperature can still fluctuate throughout the day. In order to optimize your plecostomus’ living conditions, you need to install a heater in its tank.
Adjustable heaters are preferable so that you can maintain the tank’s temperature easily. Don’t forget to consider the tank size as well. The bigger the tank, the higher the heater’s wattage.