Observations on the Biology and Fishery Of Oreochromis Mossambicus (Trewavas, 1983) (Pisces: Cichlidae) In The Lower Tana River (Kenya)

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Date
1988
Authors
Wakwabi, E.O.
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Abstract
Von Bertalanffy Growth Formula parameters: L 00 = 33.6 cm total length, and K = 0.678 per annum, were estimated on the ELEF AN 1 programme on Apple III microcomputer terminal. VBGF for this species in this area is therefore: 1.. = 33.6 (l-eo.678 t):ESP:ASP= 0.364 A length - weight relationship: LoglOW = -1.13 + 2.58 LoglOL (r=e;0.730, P = 95%) or W = 0.078. L2.58 was established for the species in this area. The mean monthly relative condition factor (Kn) was found to vary between 0.798 and 1.734 with an average annual value of 0.975. OreochrQmis mossambicus breeds throughout the year with three peaks in March, July and October and have a male dominant sex ratio during the SE monsoon season and the Septembber - November intermonsoon period. A 1:1 sex ratio was observed for the early part of the year i.e., during the NE monsoon (December - February) and the March - May intermonsoon period. Annual coefficient of total mortality (Z = 2.982); natural mortality rate (M = 1.352); fishing mortality rate (F = 1.630); and an exploitation rate (E = 0.540) were estimated for this species. Seasonality in these parameters was also observed to reflect their relationship to the rainfall and river volume regime patterns.
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East African Agricultural And Forestry Journal, LIV (1-2), p. 19-31
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