Effect of Broodstock Density on Oreochromis shiranus Fry Production in Hapas

Oreochromis shiranus broodstock were stocked in 3 x 3 x 1 m hapas for 413 days in Malawi at 1.7, 1.0, and 0.7/m2 (sex ratio was 1 male: 2 females). First sampling was done 14 days after stocking and every 21 days thereafter. Free-swimming fry first appeared after 56 days. Total spawn (free swimming fry, sac fry, and eggs) were harvested every 21 days, beginning on day 224. The lowest broodstock density produced significantly (P < 0.05) more free-swimming fry and spawn per female, but the highest density produced significantly more per m2. There were positive correlations between fry/m2 and broodstock density (r = 0.92) and between spawn/m2 and broodstock density (r = 0.99), and negative correlations between fry/female and broodstock density (r = -0.96) and between spawn/female and broodstock density (r = -0.94). Water temperature influenced fry production (P < 0.05). Minimum temperatures below 19°C delayed reproduction within the 21-day cycles. Breeding ceased when minimum temperatures fell below 17°C.