Rio Negro Piranha

The blue tiger piranha has blue-gray scales, a small rhomboid body, a robust head, large eyes, and a pugnacious lower jaw. These fish are small for piranhas, as their length is usually around 13–15 cm (5–6 in) long, with a maximum length of 30 cm (12 in), while other piranhas average around 20 cm (8 in) and have a maximum length of 40 cm (16 in). S. gouldingi has 2 unbranched and 14-16 branched dorsal fin rays with a pre-anal spine. Additionally, it has 13-17 dorsal soft rays, 29-33 anal soft rays and 36 - 38 vertebrae. It has a proximal black band on its caudal fin, vertically elongated stripes on the lateral body, and no prominent vertical humeral blotch. As a juvenile, the gills and rest of the body is yellow with elongated rounded dots on its scales. These dots are dark and may dominate its body up to the gill cover. In its adult stage, it retains the yellow color on its body, with some red coloration developing near the gill area and ventral stomach, while the elongated spots disappear. Juvenile S. gouldingi have a transparent caudal fin with a black wedge, and as they age, the caudal fin becomes completely dark and the irises change to a silvery color. Due to their coloration, length, and juvenile anatomy, S. gouldingi is often confused with Serrasalmus manueli and Serrasalmus rhombeus. S. gouldingi and S. …

The geographic range of the blue tiger piranha is composed of the Amazon and Orinoco River basins of South America, particularly the Rio Negro, Rio Japura, and Rio Casiquiare of Columbia, Venezuela, Peru and Brazil. S. gouldingi prefers mineral-poor blackwater river environments with brownish, tannin-stained water, with a 4.0-7.0 pH and temperature of 24–28 °C (75–82 °F).

The name "Serrasalmus" is from the Latin serra (meaning saw) and salmus (meaning salmon), referencing a serrated keel along the stomach. The "gouldingii" species epithet refers to ecologist Michael Goulding, in honor of his efforts in collecting Amazonian fishes.