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International Journal of Aquaculture, 2014, Vol.4, No.15 89
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acids, nucleotides, phospholipids, proteins, and a
key component of many coenzymes. These
compounds function in energy releasing cellular
reaction, cellular division and growth, in the
transport and metabolism of fats, and in the
absorption and utilization of carbohydrates, fatty
acids, and proteins. Thus P is an essential nutrient
for growth, skeletal development and reproduction
in fish (Asgard and Shearer, 1997). Phosphorus
deficiencies induce skeletal deformities such as
curved spines and soft bones in Atlantic salmon,
cephalic deformities in common carp, scoliosis in
haddock and halibut (Lall and Lewis-McCrea, 2007).
However, Baruah et al. (2007b) reported that addition
of 3% citric acid activated microbial phytase in feed
of rohu increased absorption of Na, P, K, Mn, Mg, Fe,
Zn and N in whole body and plasma. Masumoto et al.,
(2001) observed that P concentrations in whole body
and plasma were higher in Japanese flounder fed a
phytase supplemented compared to the control which
is in the support with this present study. Similarly,
Jackson and Robinson (1996) reported that inclusion
of phytase in the diet of fish at 1,000 units per kg or
higher significantly increased the mineral content of
bone-especially the concentration of calcium,
magnesium, phosphorus and zinc. Bransden and
Carter, 1999 reported a significant increase in nitrogen
and mineral digestibility of flat fish, Greenback
flounder (
Rhombosolea tapirina
) fed soybean phytase.
The findings of the reports were in agreement with the
present study.
The minerals deposition in the faeces of the fishes
after the feeding trials showed that the deposition were
significantly higher in the faeces fishes of the fed diets
without phytase than in the feaces of the fish fed diet
with phytase. The result showed that phytase inclusion
in the diets of
O. niloticus
could successfully reduce
the minerals availability in faeces. Discharge of high
levels of soluble P from fish culture systems into open
water environment stimulate phytoplankton growth,
resulting in wide fluctuations in dissolved oxygen
concentrations (Li et al., 2004). Many studies have
reported a clear effect of phytase supplementation in
reducing P excretion from fish. Ai et al., (2007)
showed that the total P effluent was significantly
lowered when fish reared with a diet supplemented
with phytase (200 FTU/kg). Similarly, soybean meal
based diets supplemented with phytase decreased the
excretion of P from red sea bream and maximum
reduction was reported at 2000 FTU/ kg feed (Biswas
et al., 2007). Similar results were also observed for
rainbow trout (Sugiura et al., 2001).
Faecal waste of P in rainbow trout was reduced by
phytase supplementation in soybean protein concentrate
diet (Vielma et al., 1998) and a significant decrease
was noticed when practical diet supplemented with
phytase at a level of 2000 FTU/kg (Vielma et al., 2001)
was fed. Phosphorus concentration in faecal matter
was reduced when trout were fed a diet with phytase
supplemented at 500 and 1000 FTU/kg compared to
non-supplemented feed (Verlhac et al., 2007).
Storebakken et al., (2000) observed that phytase
treated soy protein concentrate based diet induced
significantly lower excretion of P compared to when a
fishmeal diet was fed to Atlantic salmon. Phosphorus
content of faeces was also reduced in Atlantic salmon
fed a phytase supplemented diet (Sajjadi and Carter,
2004). In juvenile catfish,
Ictalurus punctatus
,
Li and Robinson (1997) reported that microbial
phytase supplementation in diets reduced the excretion
of faecal P by about 60%.
Exogenous phytase was substantially efficient in
enhancing the bioavailability of P and thus reducing
the amount of faecal-P. Thereby, inclusion of phytase
in aqua feed tends to reduce the phosphate load from
fish wastes and thus eventually prevents phosphate
induced algal bloom contamination. Any reduction in
P excreted by fish and other animals is of benefit to
both the environment and sustainable production
(Baruah et al. (2007a). Many studies suggest potential
environmental benefits to the extent of 30% to 40%
reduction in P excretion (Omogbenigun et al., 2003).
Sugiura et al., (2001) reported that excretion of P in
the faeces of fish fed a low-ash diet containing
phytase-treated soybean meal was reduced by 95-98%
compared with P excretion by fish that consumed
commercial diet without phytase. These ascertain
supports the observation from the present study that
the total wastes of P effluent were significantly
reduced by phytase treatment of the different
experimental diets compared to the control diet.
3 Conclusion
Plant ingredients have limitations due to the presence
of phytate and other anti-nutritional factors that