Pond loach

A small, elongated freshwater loach (family Cobitidae) native to East and Southeast Asia (China, Japan, Korea, Vietnam). Adults reach 15–25 cm with an eel-like, cylindrical body, small scales embedded in mucus-covered skin, 5 pairs of barbels around the mouth, and olive-brown to grayish coloration with darker spots or mottling. They inhabit soft-bottomed ponds, rice paddies, streams, and marshes. They are benthic, burrowing into mud, and can breathe air by gulping atmospheric oxygen and absorbing it through the intestinal lining (intestinal respiration)—enabling survival in stagnant, hypoxic waters. Their common name "weatherloach" comes from increased activity before stormstheir common name "weatherloach" derives from increased activity before storms, presumably due to sensitivity to barometric pressure changes. They are omnivorous bottom-feeders, eating insect larvae, worms, detritus, and organic matter. They are an important food fish in East Asia (especially China, Japan, and Korea) and a popular aquarium species. They are hardy, tolerant of poor water quality and temperature extremes. Reproduction involves external fertilization; females lay thousands of small adhesive eggs. Some populations are naturally polyploid (diploid, triploid, tetraploid), exhibiting unusual reproductive modes including gynogenesis and hybridogenesis. They have been introduced to many countries (Australia, USA, Europe) and are considered invasive in several regions, competing with native loaches and bottom-dwelling fish. They are used in aquatic toxicology and environmental monitoring as bioindicator organisms. The genome has been studied in the context of polyploidy and unisexual reproduction. 2n=50 (diploid populations). Lifespan: 7–10 years. IUCN: Least Concern.