Length-weight relationship, body condition and sex ratio of tilapia (Oreochromis niloticus l.) in Lake Chamo, Ethiopia

  • Yirgaw Teferi National Fisheries and Other Aquatic Resources Research Center (nflarr), Ethiopian Agricultural Research Organization (earo), PO Box 64, Sebeta, Ethiopia
  • Demeke Admassu Department of Biology, Faculty of Science, Addis Ababa University, PO Box 1176, Addis Ababa, Ethiopia


The length-weight relationship of 1429 fish ranging in size from 120 to 610 mm Total Length (tl) and from 36 to 4800 g Total Weight (tw) was computed based on monthly samples collected between March 1996 and March 1997. The relationship between total length and total weight for both sexes was curvilinear and statistically significant. The regression equation for the females was TW=0.0225TL2.97 r2=0.98, P<0.05 and that for the males was TW=0.0211TL2.99 r2=0.98, P<0.05. There was a significant variation in the mean monthly condition factor of both sexes (anova, P<0.05). The mean ± SE Fulton's condition factor ranged from 2.10 ± 0.03 to 2.35 ± 0.10 for the males, from 1.96 ± 0.03 to 2.1 ± 0.04 for the females. Sex ratio of O. niloticus was not significantly different from 1:1 in the total samples. However, numerically females were significantly more (P<0.05) in number than males in samples taken between March and May whereas males dominate in samples taken between October and February. There was also a significant variation in sex ratio in samples of fish larger than 400 mm tl and dominated by males (P<0.05). However, sex ratio did not deviate significantly from the theoretical ratio 1:1 (P>0.05) in samples of fish less than 400 mm tl.

Key words/phrases: body condition, Ethiopia, length-weight relationship, Oreochromis niloticus, sex ratio

SINET: Ethiopian Journal of Science Vol.25(1) 2002: 19-26