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BiologyFreshwater (Ref. 89241). Found in streams, rivers, and lakes over substrates of firm mud, silt, and rock (Ref. 57533). 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 (Ref. 89241). Ammocoete larval stage duration also cited as four years (Ref. 57533). 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 a shrinkage in their total length. Metamorphosis occurs in April-August (Ref. 89241). Parasitic (Ref. 57533). Following metamorphosis, adults migrate to Lake Chapala or the Duero River (Lerma River Basin) where they live as ectoparasites of fishes (carp and catfish) for two years. The diet appears to be predominantly blood. A large number of scales of Moxostoma austrinum and either of Algansea popoche, Yuriria alta, or Y. chapalae, as well as possibly Chirostoma sp. has been found mixed with blood in the intestine of adults. Attacks on the small cyprinids and the atherinopsid almost certainly resulted in their death. Around late June, early July they begin to migrate upstream to the spawning grounds in the upper reaches of the Celio River and die after spawning. Nine individuals in spawning readiness were collected on 19 November (water temperature was about 20°C). Fecundity, 6,617-9,095 eggs/female. Egg diameter, 0.7-0.8 mm. Is presumed to kill a certain number of commercial fish species (Algansea popoche and Chirostoma sp.) in Lake Chapala (Ref. 89241).