Adults migrate up to 4,827 km upstream to spawn (Ref. 6850). Migration from the sea begins in December so that the the first fish are near river mouths by spring (Ref. 27547). Once a female selects a spot, she begins to dig a nest, driving away other females during the period of nest building. The female is attended by a larger, dominant male and several smaller males who drive away other males. While the female digs the nest, the male courts her by coming to rest beside her and quivering; by swimming about over her, touching her dorsal fin with his body and fins; and occasionally nudging her side gently with his snout (Ref. 28978). Upon completion of the nest, the female drops into it and is immediately joined by the dominant male. The fish open their mouths, vibrate, and eggs and sperm are released. At this point smaller males may dart into the nest and release sperm. The female then quickly moves to the upstrem edge of the nest and begins to dig. The eggs are covered and a new nest is made. The whole process is repeated until the female releases all her eggs, which may take several days. The male then leaves the female and may mate with another female. The female guards the nest for as long as she can. Spent adults usually die a few days after spawning. (Ref. 1998, 27547).Reproductive strategy: synchronous ovarian organization, determinate fecundity (Ref. 51846).
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