Tetraodon nigroviridis is a small (up to 17 cm) pufferfish (family Tetraodontidae) found in freshwater and brackish habitats of Southeast Asia, including river systems of Indonesia, Thailand, Malaysia, Cambodia, and Vietnam. It has a rounded, stout body capable of inflation by swallowing water or air when threatened, a beak-like mouth formed by fused dental plates (two upper, two lower) used for crushing hard-shelled prey, large prominent eyes, and a scaleless skin with small spines that become erect when inflated. The dorsal surface is bright green to yellow-green with numerous black spots, and the ventrum is white. Like all pufferfish, it produces tetrodotoxin (TTX), a potent neurotoxin, in its skin, liver, gonads, and intestines, likely produced by symbiotic bacteria. T. nigroviridis inhabits mangrove estuaries, river mouths, and flood plains, preferring brackish water but often entering fresh water. It is a voracious carnivore feeding on snails, mussels, crustaceans, and other invertebrates. Its genome was sequenced in 2004 and is notable for being one of the most compact vertebrate genomes (~340 Mb), about one-eighth the size of the human genome but containing a similar number of genes. This compactness—due to reduced intergenic regions and smaller introns—made it valuable for gene identification and annotation of larger vertebrate genomes. It is popular in the aquarium trade.