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BiologyFreshwater, in rivers. Spawning habitat is a fast-flowing, clear-water stream with a stony substrate. Eggs hatch between the months of November and January and ammocoetes undergo metamorphosis at the end of three years. Ammocoetes live in the mud and feed on plankton (algae of the genera Rhizosolenia, Pleurosigma, Pinularia, Stauroneis, Amphora, and Cocconema, filamentous Chlorophyceae, rotifers, ciliates, and occasionally euglenoid flagellates). The mean total length reached at the end of the first year of larval life is 83 mm; at the end of two years, 135 mm; and at the end of three years, 146 mm. During the rainy season (July) of their first year, ammocoetes exhibit shrinkage in their total length. Metamorphosis occurs in April-August (Ref. 89241). Adults nonparasitic (Ref. 12268, 89241). After 3-4 months of adult life, spent downstream in the Duero River, they migrate a short distance (3 km) upstream to the spawning grounds in the upper reaches of the Celio River and die after spawning. The duration of the adult life is therefore at most six months. Spawning period between 19 November (when the water temperature reaches about 20°C) and 3 January. Fecundity, 990-3,456 eggs/female. Egg diameter, 0.7-0.8 mm (Ref. 89241).