International Journal of Aquaculture 2015, Vol.5, No. 41, 1-20
2
1,700 kg per hectare on research plots, which
compares favourably with the United States (US)
yields of 2000 kg/ha and Brazil yields of 1,800 kg/ha
(PrOpCom, 2007). It is the most efficient plant and
has a higher metabolizable energy, protein and
balanced amino acid profile, except methionine,
compared to other plant protein sources (Nahashon
and Kilonzo-Nthenge, 2011). However, the major
constraints that limit its use in animal feed are the
presence of fiber, starch, non-soluble carbohydrates,
and anti-nutrients that affect digestibility and fish
growth (Haghbayan and Mehrgan, 2015), one of
which is phytate (Kumar et al., 2011), which binds
minerals, including phosphorus, thereby limiting its
utilization for growth of animals (Olukosi, 2012). It is
highly heat-stable compared to other anitinutrients
that can be destroyed by heat treatment (Nahashon
and Kilonzo-Nthenge, 2011). Fish cannot digest
phytate phosphorus, which represents about 70-80%
phosphorus (Kumar et al., 2011) in plant-based diets
because they lack intrinsic gastrointestinal phytase;
therefore, in intensive fish production, large amounts
of phosphorus are discharged into the environment
where they pose serious pollution problems in aquatic
environment (Nwanna et al., 2008). Nitrogen (N) and
phosphorous (P) in metabolic waste produced by fish
are the origin of most dissolved N and P waste
resulting from intensive aquaculture operations
(Hardy and Gatlin, 2002). The excess of these two
elements in the effluents of aquaculture systems leads
to eutrophication and a consequent change in the
aquatic ecosystem (Nwanna and Olusola, 2014).
Reducing the outputs of these dissolved wastes is
considered to be a key element for the long-term
sustainability of aquaculture. Nigeria is the leading
country in Africa with the most number of people
involved in fisheries and aquaculture sector (FAO,
2014), and the African catfish (
Clarias gariepinus
), an
omnivorous species, is the leading aquatic crop in
Nigeria, cultured for its fast growth rate and stress
tolerance (Megbowon et al., 2014). The commercial
production of this species may contribute to the
pollution of aquatic environment. The concentration
of ammonia, a nitrogenous waste from protein
metabolism, is often the limiting water quality
parameter in intensive aquaculture production systems,
which affect fish growth ((Lazzari and Baldisserotto,
2008). Phytase, a hexaphosphosphate hydrolase enzyme,
which degrades phytate and improve phosphorus
availability (Olukosi, 2012), has been extensively
used in animal and fish nutrition with the benefit of
enhancing growth and nutrient utilization (Nwanna
and Schwarz, 2007; Nwanna et al., 2008) as well as
phosphorus availability (Riche and Garling, 2004; Yoo
et al., 2005), mineral availability (Debnath et al.,
2005a; Liebert and Portz, 2005), and growth (Nwanna
et al. 2005; Vielma et al., 2000; Baruah et al., 2007a).
However, the extent to which phytase generate
positive growth effect in most studies have not taken
into consideration its concormitant impact on water
quality parameters, particularly ammonia input in
aquatic environment (Lazzari and Baldisserotto, 2008).
High temperature and high pH have been reported to
negatively affect fish physiological stress response to
ammonia, depending on several factors, including
dissolved oxygen concentration (Wagner et al., 1997;
Chen et al., 2012). There is need to investigate the
effect of phytase and phytase efficacy on growth of
fish and its effect on water quality. The African catfish
has a low stomach pH of 4, which can enhance
phytase function and efficacy (Van weerd et al., 1999),
which may benefit the aquaculture environment in
terms of reduction of waste output from ammonia.
The research, therefore, is aimed at investigating the
effect of phytase on growth and some water quality
parameters in juvenile
Clarias gariepinus.
2 Materials and Methods
2.1 Experimental diets
The research investigated the effects of phytase
supplementation in soya bean, which were formulated
to contain four replacement levels of fish meal at
25 %, 50 %, 75 % and 100 % soya bean meal labelled
S0, S1, S2, S3 and S4 as basal controls with no
phytase (P0). Another four S1, S2, S3 and S4 diets
were formulated with the same composition as the
basal diets, but were supplemented with 250 FTU/g
(P1), 500 FTU/g (P2), 750 FTU/g (P3), and 1000
FTU/g (P4), respectively. One FTU (fytase unit,
Danish word) is defined as the amount of phytase that
liberates 1 μmol of inorganic phosphorus from 0.0051
mol/L of sodium phytate per minute at pH 5.5 and
37°C (Engelen et al., 1994). The fish meal diet, S0
(100%), which served as control, was included in the
experiment to compare growth performance with
phytase diets. About 10 kg of raw soya bean was
