Field-induced breeding of the dorado, Salminus maxillosus Valenciennes

Abstract

Induced breeding of the dorado was performed using broodfish held at capture sites near the river shore. Prochilodus platensis pituitary glands (Pit) and human chorionic gonadotropin (HCG) were used as stimulators of ovarian maturation and ovulation. Positive results, with the production of viable larvae, were obtained with single injections of 1 Pit/kg and with multiple injections of 0.5, 0.25 or 0.125 Pit/kg at 2.5-h intervals. Females ovulated after receiving between 0.5 and 1 Pit/kg. During the time period covered by the experiments the percentage of ovulatory responses improved from 36% in December to 86% in February. The threshold dose that triggers final maturation and ovulation was found to be between 0.125 and 0.25 Pit/kg. Latency between injection and ovulation varied from 7 to 9 h at 23.5°C. Viability of intraovarian ovulated eggs rapidly decreased to 0% in less than 4 h at 23.5–25°C. Hatching rates ranged from 0 to 63%; the best value was obtained when eggs were stripped immediately after ovulation from a female treated with five injections of 0.125 Pit/kg at 2.5-h intervals.