Bythaelurus giddingsi is a species of catfish in the family Auchenipteridae. It is found in fresh and brackish waters of South America. It reaches a maximum length of 36 cm (14 in).
The body of Bythaelurus giddingsi is stout and elongated. The head is large with a blunt snout. The eyes are small and located dorsally on the head. There are four pairs of barbels, two maxillary and two mandibular, which are used for sensing food in murky water conditions. The teeth are sharp and arranged in rows on the jaws as well as on the vomerine process and palatines.
The dorsal fin has 7-9 rays while the pectoral fins have 15-17 rays each. There are 24-26 anal fin rays present. All fins except for the adipose fin have numerous fine serrations along their margins. The caudal peduncle is thickened with strong muscles used for propulsion through water. The skin is covered with small scales that overlap each other giving it a smooth texture.
The coloration of Bythaelurus giddingsi varies depending on habitat conditions but typically consists of a dark brown or black body with lighter colored spots or blotches along the flanks and dorsal region. Juveniles often exhibit more distinct patterns than adults which tend to fade somewhat with age.