Population dynamics of Barbus barbus plebejus (Valenciennes) and Leuciscus cephalus cabeda (Risso) in the middle River Po (Italy)

Scales from 427 Barbus barbus plebejus and 406 Leuciscus cephalus cabeda from the middle River Po were examined. The last annulus was formed between April and May 1977, except the 0–1 age-group of L.c. cabeda which developed its first year-ring between March and April 1977. The survival (S) and annual mortality (A) rates were equivalent in both fish populations; the same was true of both sexes of Leuciscus, but S in Barbus males was lower than in females. The sex ratio showed a preponderance of females in both species.Growth rate from June to September 1976 was higher than in the rest of the year. Annual growth in Barbus females was higher than in males, whereas both sexes in Leuciscus showed equivalent growth rates; growth rate was higher in Barbus than in Leuciscus. The P/B ratio of both species was higher in the young age-groups.Presented at the XLVII Congress of the Italian Zoological Union, Bergamo (Italy), September 1979.Presented at the XLVII Congress of the Italian Zoological Union, Bergamo (Italy), September 1979.