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International Journal of Aquaculture 2012, Vol.2, No.10, 65
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71
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Fincha reservoir was built date back into the 1972s by
the construction of a rock-fill dam on the Mita stream,
shortly above the point where it plunges into the gorge
of the Fincha River, a tributary of the Blue Nile River
(Mesfin et al., 1988). It has a surface area of 170 km
2
and an average depth of 9 m. The reservoir area is
characterized by a sub-humid type of climate with an
annual precipitation of 1 824 mm and the monthly
mean air temperature varies from 15
℃
to 18
℃
(Table 1).
Fish were introduced into Fincha Reservoir in late
1970-ies to provide cheap protein source to the
riparian community (Mesfin et al., 1988).
Table 1 Some chemical features of Fincha Reservoir (Mesfin et
al., 1988).
Parameter
units
Values
Conductivity
µs/cm
75
pH
-
6.45
Na
+
Meq/L
1.37
K
+
Meq/L
0.19
Ca
+
Meq/L
0.58
Mg
++
Meq/L
0.20
HCO
3
-
Meq/L
2.49
SO
4
-
Meq/L
0.17
Cl
-
Meq/L
0.03
Chlorophyll-
a
µg/L
5.56
5.2 Sampling
Fish samples were collected monthly using gill nets of
different mesh size (60 mm, 80 mm, 100 mm, 120 mm
and 140 mm stretched mesh) set overnight. The total
length (TL) and total weight (TW) of fresh fish
samples were measured to the nearest 0.1 cm and 0.1 g,
respectively. Subsequently length-weight relationship
was calculated using power function (Lager, 1956):
W=aL
b
Where, “a” is the intercept, “b” is the slope of
length-weight regression, W is total weight and L is
total length. Fulton’s condition factor (k), an indicator
of the “well-being” of an individual fish was
calculated using the following formula (Lager, 1956):
K= [Weight/(Length)
3
]
×100
After dissection, the sexes were identified and
maturity stage (S) of each fish was measured using a
five scale maturity index: immature (S
1
), developing
(S
2
), ripening (S
3
), ripe and running (S
4
) and spent
(S
5
). The relationship between the percentage of
mature fish (P) per length class and fish length (
X
in
cm) was described with a logistic curve:
P
X
= 1/[1+e
(bx+a)
]
The length at first sexual maturity (L
50
) was then
derived from the relationship of a and b:
L
50
=
－
a/b
Acknowledgements
The authors thank all the technical staff members of National Fisheries and
Aquaculture Research Center (NFLARC) for their assistant during the data
collection. We also thank Mr. Ashenafi Azage for safe driving during the
field trip to fincha reservoir. This study was financed by the EIAR-National
Fisheries and Aquaculture Research Centre, Sebeta, Ethiopia.
Author’s contributions
GT and FT contributed considerably during data collection, analysis of the
result and write-up of the manuscript. GT contributes to plot the L
50
graph
was instrumental during the preparation of this manuscript.
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