Adults typically reach a length of 15–18 cm. Under optimal conditions, they can grow significantly larger; the largest officially recorded size for a spotted pimelodus was 51 cm with a weight of 2.4 kg. The species name accurately reflects its characteristic coloration: a light silvery or light gray body adorned with rows of large, regular, rounded spots. Caution should be exercised when handling these catfish, for example, during aquarium maintenance or capture. The first rays of the pectoral and dorsal fins are sharp spines capable of causing injury. The mucus covering the fish's body contains toxins that enter the wound upon puncture. For this reason, a sting from such a spine is quite painful, comparable to a bee or wasp sting, causing acute pain, swelling, and a throbbing sensation. Visually, the spotted pimelodus is similar to a closely related species – the marbled pimelodus, however, the latter is distinguished by its smaller size and less regular, unevenly shaped spots on its body.