Abstract:
The effects of total hardness on growth performance, survival, and feed utilization
efficiencies of platy fish (Xiphophorus maculatus) were studied. Twenty-one days old
180 juvenile fish with initial mean weight of 0.11±0.04g and mean total length of
1.82±0.21cm were exposed to three different hardness levels as, 50, 150, 250 mg/L and
0.00mg/L as the control. Fish were randomly assigned to three treatments and the control
each with three replicates. All the fish were kept in 50 L glass tanks at initial stocking
density of 15 fish/tank. Total hardness of the water was maintained by adding CaCl2 &
MgCl2 into the water. Fish were fed with commercial prima diet (39% crude protein)
twice per day to near satiety and experiment was lasted for 06 weeks. Water quality of
each treatment was maintained below the lethal levels. The percentage survival of fish in
each treatment was observed and recorded daily. Total length and body weight of fish in
each treatment was measured every two-weeks, while amount of feed consumed was
recorded daily. At the end of the experiment, % Average Daily Gain (%ADG), % Specific
Growth Rate (%SGR) and Food Conversion Ratio (FCR) were calculated to evaluate the
growth performances and feed utilization efficiencies of platy fish. At the end of the
experiment, significantly greatest (p<0.05) mean weight gain (0.54±0.01 g), mean total
length gain (1.57±0.05 cm), %ADG (11.62±0.21), %SGR (4.20±0.04) and significantly
lowest (P<0.05) FCR (1.54±0.05) were observed in 150 mg/L hardness level. Among
tested three levels, the growth performances were significantly highest in the hardness
level of 150 mg/L followed by 50 mg/L. Final percentage survival was not significantly
(p>0.05) different among treatments. According to the overall results, significantly
highest and lowest growth performances were observed in 150 mg/L and 250 mg/L
hardness levels respectively, while moderate growth performances were observed in 50
mg/L. Correlation coefficient between the total hardness and %SGR of fish was 0.818
and it clearly showed that, around 150 mg/L total hardness level is more favorable for the
growth of platy fish. Results of this study revealed that, 150 mg/L total hardness level is
the best tested levels for the growth performances and feed utilization efficiencies of
Xiphophorus maculatus. However, above, and below 150 mg/L total hardness levels are
negatively affected the growth performances & feed utilization efficiencies.
