Protosalanx pyalocranius is a small fish, but has fishery importance in HongzeHu. Investigation on the biology of this fish, including spawning, and embryologicaldevelopment, feeding habit, growth and life--span, was made mainly during the years1974--1975. Its diagnoses are the following: Body slender, elongate, subcylindrical anteriorly and compressed posteriorly. Headmuch depressed, with long, flat, pointed snout. Maxillaries ending beyond anteriorborder of eye; lower jaw projecting; two series of teeth on each side of the palatinelower jaw and tongue each with two series of teeth; no fleshy praesymphysial append-age; dorsal fin wholly in a short distance before anal, with about II, 15--17 rays; andanal III, 27--32 rays; petoral fin with a flaplike strang muscular base, with about24--27 rays; candal foked; vertabrae 67--70. Individuals of one year old attain sexual maturity. Spawning season begins from December 10th to March 10th of next year. Ripe eggs with external filaments. Spawn-ing is in the lake bay. Fertilized eggs sink to the bottom of the lake and hatch to friesin about a month at a temperature range of 4. 3°--8. 9℃; after spawning the parentssoon die. The feeding habit chinges with growth of the fish and the main food items forJuveniles below 70 mm. consist of Cladocera and Copepoda. When they attain a bodylenth of about 70 mm., they eat small fish and prawns. The fries grow fast, after three or four months, they reach fishing standards(40--70 mm.). If some measures of protection are taken for their propagation, the fish-yield may be increased.