Pseudaspius hakonensis is a freshwater fish species in the family Cyprinidae, native to East Asia, particularly Japan, where it is commonly found in rivers, lakes, and marshy environments. The genus name Pseudaspius combines Greek pseudo- (“false”) with Aspius, a genus of freshwater fishes, indicating its taxonomic resemblance to related cyprinids, while the species epithet hakonensis refers to Hakone, a region in Japan where the species was first described. It is commonly known in Japanese as ugui (ウグイ), a fish with both ecological and regional culinary importance.

This species is a medium-sized cyprinid with an elongated body, silvery coloration, and well-developed fins suited for active swimming in flowing freshwater systems. It is adaptable to a range of habitats, including streams, rivers, and lakes, and often migrates between freshwater and brackish environments depending on seasonal conditions. Its diet consists of algae, aquatic plants, small invertebrates, and organic detritus, making it an omnivorous component of freshwater ecosystems.

Pseudaspius hakonensis has been traditionally consumed in certain regions of Japan, particularly in inland and mountainous areas where freshwater fishing is common. It may be grilled, salted, or prepared in rustic dishes, though it is less commercially prominent than marine fish species. The flesh is relatively lean and mild in flavor, and in some cases the fish is processed through drying or fermentation to enhance preservation and taste.

Nutritionally, Pseudaspius hakonensis provides high-quality protein, essential amino acids, and trace amounts of omega-3 fatty acids typical of freshwater fish. It also contains micronutrients such as phosphorus and B vitamins. Bioactive compounds include small peptides generated during digestion and processing, which have been studied in fish more broadly for potential antioxidant and antihypertensive effects.