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International Journal of Aquaculture, 2013, Vol.3, No.6, 23
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29
28
seine net and their mean body weights and total lengths
were recorded.
In each pond, the
total dissolved substances
(
TDS), conductivity and transparency were measured
using appropriate probes after every fortnight.
All the
water test meters were calibrated before use. Surface
water samples for nitrates, phosphates and ammonia
analyses were collected using sterilised clean
500
mL
polythene bottles. The samples were placed in a cooler
box and then taken to the laboratory for analyses.
4.4
Data analysis
Specific growth rate (SGR) was calculated from data on
changes in body weight over a given time intervals
according to the method of Brown (1957) as follows:
%100
T
LnW LnW
SGR
ip
ik
Where, W
ik
= final mean individual fish weight; W
ip
=
initial mean individual fish weight; T = number of
days elapsed.
Survival rate was calculated as follows:
%100
y
x
N
N SR
Where N
x
= number of fish harvested; N
y
= number
of initially stocked.
Percentage weight gain was calculated as follows:
%100
WO
WO Wt
WG
Where Wt = final weight; WO = initial weight.
Condition factor was calculated as follows:
100
3
2
2
L
W Cf
Where: W
₂
= Final fish weight; L
₂
= Standard length.
Two way analysis of variance (ANOVA) was used to
determine if there was any significant difference in
the growth rates, final weight, final length and survival
rate of the harvested fish of the three treatments and to
test for significant differences within the physic-chemical
parameters and growth parameters at 5% level of
significance using the SysStat 12 for Windows version
12.02.00 (
Systat, 2007).
Acknowledgements
The field assistance of staff at Lake Chivero Fisheries Research Station
(
National Parks) and provision of ponds is greatly acknowledged. Our
gratitude extends to Michael Tiki for his invaluable input into this
research.
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