STUDIES ON THE REPRODUCTIVE BIOLOGY OF PELTEOBAGRUS VACHELLI (RICHARDSON)

From October 1996 to September 1997, 941 specimens collected in the middle reaches of Yangtze River for the studies on the reproductive biology of Pelteobagrus vachelli (Richardson).During the spawning periods from April to July, stages 4, 5, or 6 of the ovaries were found, and the gonadosomatic index (GIS) is much higher than that in the other months.The absolute fecundity of P.vachelli ranges from 1088 to 19675 eggs with a mean of 7728 eggs, and the relative fecundity varies from 42 to 58 eggs with a mean of 55 eggs.The relationships between the absolute fecundity and body length (L), body weight (W), and age (Yr) could be expressed as F= 0.04L231, F= - 3388.22 + 111.79w -0.16w2, and F= - 4743.03 + 5726.22yr - 418.32yr2, respectively.The sexual ratio of female to male is 1:1, and no obvious difference between the spawning and non-spawning periods.Age of the first maturity is 2 years old.The minimum size of matured female and male are respectively 133 and 161 mm in body length.The spawning stock mainly consists of age 2 and 3 groups.