Author(s):

Kefi AS, Mumba CD, Mupenda N, Kujila GM and Chilongo R

Abstract: A study was conducted to determine sex – dependent index of preponderance and condition factor of Oreochromis andersonii in fertilized fish ponds. Fish (0.52±0.093g; mean ± SD) were stocked in semi – concrete ponds at 4 fish/m² and were allowed to grow for 281 days. There was a negative allometry for both sexes since the ‘b’ factor was lower than 3 although females’ (3.773±0.069) coefficient of condition (K) was significantly (P<0.05) lower than that of males (3.972±0.040). Oreochromis andersonii females showed a logarithmic relationship between the heart (y = 0.037ln(x) - 0.0836; R² = 0.407; P<0.05) and liver (y = 0.2214ln(x) - 0.1756; R² = 0.317; P<0.05) weights and body weight while in males there were linear relationship for both heart (y = 0.0213 + 0.0009x; R²= 0.406, P<0.05), and liver (y = 0.0459 + 0.0097x; R²= 0.40, P<0.05). A power relationship was observed between length – weight relationship for both sexes (female = y = 0.0001x^2.7672; R² = 0.943; P<0.05 and male = y = 0.0001x^2.7628; R² = 0.972; P<0.05). Stomach analysis revealed a higher index of preponderance for artificial feeds in males (55.73%) than females (52.52%). Females (47.48%) selected natural foods more than the males (44.27%) fish. However, the male (2.199±0.139%) fish had a significantly higher Relative Stomach Weight than females (1.592±0.147%). Growth indices favored males with both Specific Growth Rate (2.228±0.01% day^-1) and Body Weight Gain (157.589±3.422g) being significantly (P<0.05) higher than those of females (SGR% day^-1= 2.11±0.014; BWG = 117.804±3.987g). The culture of O. andersonii males should be promoted since they consume more of natural feeds and grow faster than the females. In rationing the feed, 2.2% of the total body weight should be considered for males production while 2.0% in mixed sex production at every feeding.

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