Non-parasitic lamprey. Adults occur in the sea and spawn in reaches of rivers and streams with strong current. Ammocoetes larvae reach up to 13 mm TL and get up to 3 years old. They live in bottom deposits and feed on diatoms and detritus. In the intestines of adults, only the remains of algae and higher plants are found. However, they may also feed on dead fish and are known to attach themselves to trout, presumably for transport. A 22% reduction in total length occurs from the pre-spawning to the spawning period. Adults die after spawning. The flesh is reported to be poisonous to eat and must be treated before consumption. Until 1868, all catches were dried and used as candles or for production of oil. Only thereafter it was used as food for humans, and is now considered a valuable and delicious fish.