International Journal of Aquaculture, 2016, Vol.6, No.7, 1
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Table 2 Water quality parameters (mean ±SE) measured during the experimental period
PARAMETER
TREATMENT
P-Value
Egg yolk diet
Raw soymilk
Roasted soymilk
Temperature
Morning
23.022 ±0.227 9
a
23.050 ±0.212 6
a
23.022 ±0.216 7
a
0.994
Afternoon
26.639 ±0.470 5
a
26.728 ±0.500 8
a
26.856 ±0.454 7
a
0.988
pH
Morning
7.84 - 8.08
a
7.85 – 8.075
a
7.834 - 8.154
a
0.613
Afternoon
7.88 - 8.07
a
7.87 - 8.11
a
7.88 - 8.05
a
0.518
DO
8.601 ±0.346
a
7.400 ±0.26
b
6.508 ±0.228
bc
0.007
Ammonia
0.098 ±0.031
a
0.887 ±0.069
b
0.811 ±0.078
b
0.000 216
Note: *
Means with different superscript within the rows indicates significant differences (p<0.05
Ammonia concentration in all treatments was however found to be above the recommended limit of 0.05 mg/l for
optimal growth and survival (Pillay, 1990). Ammonia concentration in treatments 2 and 3 (where soymilk was fed
to fry) was significantly higher than treatment 1 (egg yolk based diet). This is somewhat expected as in both
treatments, the protein rich soymilk was directly released into the culture medium. This resulted in high
concentration of ammonia as ammonia is a waste product of protein. However, the ammonia concentrations in all
treatments were below the maximum tolerable limit of 1 ppm (1 mg/L). Thus, the study shows that if a proper
water quality management regime is followed, as the one followed in this study, it is possible to keep ammonia
levels within tolerable levels. The study also showed that application of soymilk in rearing tanks has no effect on
other water quality parameters that were monitored during the experiment.
3 Materials and Methods
The experiment was conducted at the Bunda fish farm of The Lilongwe University of Agriculture and Natural
Resources located 2 Km from the main campus. The campus is located 32.5 Km south of Lilongwe city in the
central region of Malawi. The site was chosen due to availability of technical support and materials that were
required during the course of the study (Figure 2).
Figure 2 Study area (Source:
)
Note: Satellite view of Bunda Fish Farm, the study site
3.1 Experimental Fish
Clarias gariepinus
larvae were obtained by semi-artificial propagation of selected brood stock at the Bunda fish
farm hatchery using the method described by de Graaf and Jensen (1996). Brood stock in ponds at the farm were
inspected for readiness to breed and six brooders (2 females and 4 males) with body weights between 265-350 g
were selected for breeding. The selected fish was then injected with Aquaspawn (Spawnrite Ltd) at a full dose of
