Data of overall growth performance and feed utilization are presented in Table 2 .
Fish fed the low fish meal without P supplement showed the lowest final average bodyweight
of all experimental groups.
In contrast, those fish fed the diets supplemented with inorganic P showed an improved weight gain
and feed conversion ratio comparable to the control group.
The same trend was observed during all the experimental periods.
In both trials the final bodyweights and specific growth rate were not influenced by the dietary P
at the levels of 8.7 and 9.6 mg/g which were derived from supplementation with 1 and 2 mg
avlable P/g diet (Table 1)
Mortality was not observed during the trials and fish remained apparently healthy without external
signs of abnormality.
The results of each trial showed that P retention decreased gradually in the groups of fish fed
the diets containing more than 8.7 mg total P/g diet.
But fish fed the experimental diets with low-P contrent retained significantly higher amounts of P
than the fish fed the control diet (Table 3,4)
The calculation of the N retention at the end of each experiment gave lower values for the group
on the experimental diet without complementary P.
The retention and absoprtion of P and N for the second experiment is summarized in Table 4.
In this experiment, the absorption of N was quite high in all treatments, ranging from 94.1 to 95.6%
and it was not affected by the level of inclusion of dietary P supplementation.
The absorption of P was lowest in the experimental diet without MCP.
However, P absorption increased in the groups of fish fed the experimental diets with
water-solubel P supplemantation, such as MCP
P-loading values significantly increased as fish were fed higher levels of P.
Total P loading was calculated based on the P retention and te results for all trials revealed
the same tend of maximum P retention in the experimental diets with less P content
in comparisom with the control diet.
Values of P loading for the basal diet without MCP supplementation ( 3.8 mg/g estimated
available P) were the lowest, but this diet was deficient in relation to the minimum P requirement
for normal growth and feed utilization.
Another consequence of the lack of available P in the basal diet (PS0) was the considerable
reduction of the N retention efficiency and as a direct result the increment on N loading
in comparisom with the rest of the experimental diets ( Table 3,4)
Increasing dietary available P in the basal diet improved N retention and thereby lowered
its excretion
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