Growth Performance of Nile Tilapia (Oreochromis niloticus) Fed Processed Soybean Meal Based Diets Supplemented With Phytase  

S. E. Olusola1, 2 , L.C. Nwanna2
1. Department of Aquaculture and Fisheries Management, University of Ibadan, Ibadan, Nigeria
2. Department of Fisheries and Aquaculture Technology, Federal University of Technology, Akure, Nigeria
Author    Correspondence author
International Journal of Aquaculture, 2014, Vol. 4, No. 8   doi: 10.5376/ija.2014.04.0008
Received: 24 Dec., 2013    Accepted: 08 Jan., 2014    Published: 24 Mar., 2014
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This is an open access article published under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
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Olusola and Nwanna, 2014, Growth Performance of Nile Tilapia (Oreochromis niloticus) Fed Processed Soybean Meal Based Diets Supplemented With Phytase, International Journal of Aquaculture, Vol.4, No.08: 48-54 (doi: 10.5376/ija.2014.04.0008)

An 8-week feed trial was conducted in glass tanks (60×30×30cm) to assess the performance of fingerlings Nile Tilapia (Oreochromis niloticus) fed diets containing soybean meals processed by toasting and incubation methods. Six diets were formulated at 30% crude protein content with 0 (control), 2,000 units, 4,000 units, 6,000 units, 8,000 units and 10,000 units phytase/kg diet making diet/treatments. Each treatment was replicated twice, each replicate contained 15 fish (6.23 ± 0.1g). Fish were fed twice daily at 5% of their body weight. Mean Weight Gain (MWG), Specific Growth Rate (SGR), Feed Conversion Ratio (FCR) and Protein Efficiency Ratio (PER) were measured. Temperature, Dissolved oxygen and pH were determined using standard methods. Data were analyzed using descriptive statistics and ANOVA at p= 0.05. Results showed that fish fed diet 5 (8,000 units phytase/kg diet) had the best growth and nutrient utilization indices while fish fed the control diet (0 unit phytase/kg diet) had the poorest. The SGR, FCR and PER of the group of fish fed diets with 0, 2,000, 4,000, 6,000 and 10,000 units phytase/kg diet were not significantly difference (p > 0.05), while the SGR, FCR and PER of fishes fed diet with 8,000 units phytase/kg diet were significantly (p < 0.05) better than those of the fishes fed other diets. The values of temperature, dissolved oxygen and pH were closely related and were within the range for fish culture in the tropics. The results suggest that phytase inclusion in the diet of O. niloticus could be a potential and promising dietary supplementation that would positively influence growth and water quality of O. niloticus in aquaculture.
Oreochromis niloticus; Soybean; Performance; Phytase; Water quality

The main goals of aquaculture industry are to optimize growth and to produce high quality fish (Bello et al., 2012). Aquaculture has evolved as the fastest growing food producing sector and developed as important component in food security (Ibrahem et al., 2010). Fish is a high quality food containing first class protein and nutrients, important for human health and growth (Olaifa et al., 2010). In fish culture, supplementary feeding plays major roles in determining the nutritional and economic success of aquaculture.

Feed formulations account for more than 50% of the total production cost in modern intensive aquaculture (Ibrahem et al., 2010). Increasing feed efficiency especially by improving the metabolic assimilation of dietary nutrients, is of high priority in contemporary animal production (Ibrahem et al., 2010). The aquaculture feed industry relies on the fishmeal, which is the most preferred protein source for fish feed owing to excellent amino acid and fatty acid profile. Limited supply, high cost and stagnant production level restrict its use for sustainable farming (New and Wijkstro¨m, 2002, Baruah et al., 2004). The replacement of fishmeal with extensively available plant or grain by-products is getting increasing attention for the development of low-cost fish feed (Carter and Hauler, 2000; Gatlin et al., 2007). Of all the plant protein feedstuffs, soybean meal is considered to be the most nutritious and it is being used as a protein source in many fish diets (Lovell, 1988).
Tilapia belong to the Cichlidae, the family Cichlidae is very diverse and widely distributed throughout Africa, South America and other parts of the world. They are substrate spawners that guard the developing eggs, fry and are generally herbivorous of between 7 – 16 gill - rakers on the lower part of the first arch. Nile Tilapia (Oreochromis niloticus) is one of many economical freshwater fishes that are cultured in Nigeria and other parts of the world for its excellent biological characteristics.
However, there are a large number of feed additives available to improve fish growth performance, enzyme (phytase) are feed additives can be used as a growth promoter but the mechanism of action of phytase as a growth promoter is yet to be adequately researched. It was considered that phytase could have the ability to increase bioavailability of nutrients in plant protein. This study was conducted to assess the performance of O. niloticus fingerlings fed diets containing differently processed soybean meals supplemented with phytase.
1 Results
1.1 Proximate composition of the experimental diet

The crude protein of the diets was similar and ranged between 30.8 and 31.5%. The values of the ether extract, ash content, crude fibre and nitrogen free extract were similar and ranged between 16.31 and 16.96%, 8.1 and 8.3%, 10.9 and 12.05 and 31.69 and 33.79% respectively (Table 1).


Table 1 Proximate composition of the experimental diet (DM)

1.2 Proximate composition of the fish before and after the experiment

The result of the proximate composition of the initial and final body composition of tilapia fingerlings fed on the experimental diets is presented in Table 2. The fish fed diet 5 had the highest numerical value of crude protein while the least value was obtained from fishes fed diet 2. The highest ash content value was obtained from fishes fed diet 1, 2, 3 and 6 while the lowest value was obtained from fished fed diet 4 and 5.The fat content composition was highest in fishes fed diet 6 while the least composition recorded in fishes fed diet 1. The highest crude fibre (%) was obtained from fishes fed diet 1, 3 and 6 while the lowest value was obtained from fished fed diet 2 and 5. Fishes fed diet 6 had the lowest value of Nitrogen Free Extract (NFE), while those fed diet 2 had the highest.


Table 2 Proximate composition of fish before and after the experiment

1.3 Growth and nutrient utilization of Nile Tilapia fed phytase diets
The growth response of Nile tilapia fingerlings fed on diet containing varying levels of phytase is shown in Table 3. The highest value of mean weight gain was obtained from fish fed diet 5, followed by the fish fed diet 6 while the lowest value was obtained from fish fed diet without phytase (control diet). There were significant differences in the mean weight gain of the fish among the treatments.


Table 3 Growth performance and nutrient utilization of Nile tilapia fed phytase diet

The specific growth rate of fish fed diet 5 was significantly (p < 0.05) higher than the specific growth rate of fishes fed other diets, while the specific growth rate of fishes fed diets 1, 2, 3, 4 and 6 were similar (p > 0.05). The value of the feed conversion ratio followed the same trend while protein productive value, nitrogen metabolism, gross feed conversion efficiency and apparent net protein utilization were significantly (p < 0.05) among the treatments.

1.4 Water quality parameters of experimental tanks
The water quality parameters of the experimental tanks, temperature, dissolved oxygen and pH were closely related. The values varied from 24.00 to 26.03, 5.9 to 6.7mg/L and 6.8 to 7.5 respectively (Table 4).


Table 4 Mean Weekly Water Parameters

2 Discussion
In this study, experimental diets were formulated with different levels of phytase for O. niloticus fingerlings. The proximate composition of the experimental diets of this study supports the growth of O. niloticus finger- lings and this corroborate the report of Eyo (1995) that for growth at maximum rate, fry, fingerlings and juveniles must have a diet in which nearly half of the digestible ingredients consist of balanced protein.The proximate composition of O. niloticus fingerlings before and after experiments fed on experimental diets is presented in Table 3. The results indicate that the diets supported the growth of fish as increased body protein levels were recorded in all the treatments. This also showed that the protein requirement for the O. niloticus fingerlings was met for body maintenance and growth. The reason for this might be as a result of presence of phytase supplementation enhances digestibility of minerals which are bound to phytate. The higher body protein deposition and increased weight gain is indicative of the adequacy of the protein content and higher protein intake.

Results from the present study demonstrated that incorporation of phytase in toasted and incubated soybean meal diets improved overall growth performance in O. niloticus. The results of the study showed that fishes fed diets with phytase had higher mean weight gain, specific growth rate, protein efficiency ratio, feed conversion ratio, gross feed conversion efficiency and nitrogen metabolism than the group of fish fed diet without phytase. The enhancement of the growth performance in the fishes feed that contained phytase increased with the increased in the levels of phytase addition. This improvement could be attributed to the liberation of more phytate phosphorus (P) from the diets by the phytase enzymes, which the fishes utilized for the better performance. The higher performance could also be ascribed to higher dietary nutrients bioavailability and digestibility made possible by the phytase enzymes.
The results of this present study was similar to the report of Jackson et al. (1996) who reported an increase in weight gain in channel catfish fed phytase-supplemented diets containing only plant protein sources. Also, similar performance of rainbow trout (Vielma et al., 1998, 2002) and stripped bass (Papatryphon et al., 1999) was also reported and attributed solely to improved use of P from the phytate. Vielma et al. (2004), in rainbow trout and Debnath et al. (2005a), in Pangasius pangasius and Liebert and Portz (2005), in Nile Tilapia, also observed improvement in growth performance when fed phytase-supplemented diet and attributed this to increased bioavailability of protein and minerals.
The positive effect of phytase on the growth performance of the fingerlings in the present study is consistent with the results obtained by various authors (Forster et al., 1999, Cheng and Hardy, 2002, Zongjia et al., 2003). However, some authors (Vielma et al., 2000, Masumoto et al., 2001, Yan and Reigh 2002, Sajjadi and Carter 2004, Yoo et al., 2005) have reported no effect of dietary phytase on weight gain of various fish species fed plant-based diets. This discrepancy in their results may be associated with differences in their diet composition and also to different rearing conditions. Also the present study support the report of Baruah et al., (2007a, 2007b) who reported that supplementation of microbial phytase in the diets had a positive effect on the growth performance of Labeo rohita juveniles.
Specific growth rate and condition factor reflect the health status in fish (Ibrahem et al., 2010). The results of specific growth rate revealed that treatment 5 (8,000units phytase/kg diet) (0.42 ± 0.04g) had better growth rate compared to the control, they were significant differences (p < 0.05) between the treatment and the control diet. This observation was similar to Vielma et al. (2001) who reported that the specific growth rate and feed conversion ratio were significantly improved when trout were fed with phytase supplemented diet at 2000 FTU/kg feed (containing 55% of soybean meal)
Feed Conversion Ratio (FCR) is used to assess feed utilization and absorption (conversion of feed to flesh). FCR was best (0.89 ± 0.01) with treatment 5 (8,000 units phytase/kg diet) and least recorded in control (1.60 ± 0.09), there were no significant difference (p > 0.05) among the treatments except treatment 5 that was difference (p < 0.05) from the control. The result revealed that diet containing 8,000 units phytase/kg diet (treatment 5) was better utilized by O. niloticus fingerlings than control diets.
The result of the experiment also, showed that treatment 5 recorded the highest value of protein efficiency ratio and nitrogen metabolism of 0.17 ± 0.02g and 308.86 ± 0.01g respectively. Based on these parameters, the best performance is treatment 5 (8,000 units phytase/kg diet) while the lowest was recorded in the control. Feed Efficiency Ratio (FER) and Protein Efficiency Ratio (PER) are used as quality indicators for fish diet and amino acid balance. So, these parameters are used to assess protein utilization and turnover. These results are also in agreement with those obtained by Baruah et al. (2007) who recorded increase in FCR and PER of Labeo rohita fingerlings fed experimental diets containing various levels of microbial phytase for 60 days compared to the control which had the least value.
Apparent net protein utilization recorded during the experiment was highest in treatment 5 (8,000 units phytase/kg diet) and there were significant differences (p < 0.05) among the treatments. This results support the report of Debnath et al. (2005b) who reported that phytase supplemented diet in pangus increased apparent net protein utilisation.
The water quality parameters; temperature, dissolved oxygen and pH were measured during the experiment. The values obtained for the parameters were within the recommended range for warm water fishes (Boyd, 1981). From the result obtained phytase could be used in aquaculture as they did not alter the water quality.
3 Conclusion
Capture fisheries have failed to meet the demand of Nigeria populace and to bridge this gap aquaculture as been giving priority. There is a need to enhance awareness among fish nutritionists and the fish feed manufacturing industry on the use of phytase as an effective and efficient approach in the formulation of cost effective, growth promoting and low polluting fish feeds based on plant protein sources, for profitable and sustainable aquaculture production. Therefore considering the result of the experiment, I strongly recommended phytase at 8,000 units phytase/kg diet for fish farmers who want to embark on large-scale fish production.
4 Material and Methods
4.1 Experimental system
The experiment was carried out using twelve glass tanks (60 × 30× 30 cm) for 8 weeks in the Department of Fisheries and Aquaculture Technology Laboratory of the Federal University of Technology, Akure, Nigeria. The water level in each tank was maintained at a depth of 0.45 m throughout the experiment and replaced every three days to maintain relatively uniform physico-chemical parameters and prevent fouling from feed residues. The source of water was from Federal University of Technology, Akure water station. Each tank was well aerated using air stones and aerator pumps (Cosmos aquarium air pump, double type 3500 50Hz, 2.5w-3w) as described by Lawson (1995). The dissolved oxygen content and pH of the water were measured using dissolved oxygen meter (Jenway 3015 pH meter, 0.0 accuracy; Genway, Staffordshire, UK) after standardizing the meter and water temperature by a bulb thermometer (Paragon Scientific Ltd, Birkenhead, Wirral, UK).
4.2 Experimental procedure & feeding trials
There were six dietary treatments each having two replicates, with 15 fish each with a mean initial body weight and standard length of 6.23 ± 0.1g.The fish were weighed, distributed into experimental tanks and allowed to acclimatize for 14 days before the experiment. The experiment lasted for 8 weeks during which the fish were fed at 5% body weight twice daily. The diet per day was divided into two; 2.5% given in the morning by 8.00 – 9.00 am and 2.5% in the evening by 5.00 pm. Weight changes were recorded weekly and feeding rates adjusted to the new body weights.
4.3 Treatment of soybeans and diet formulation
Soybean (Glycine max) bought from a market in Akure, Ondo State was processed by using heat treatment method. The soybean was weighed using electronic weighing balance and toasted for 10 hours at 70 and ground into fine powder to form a meal. 5.1 kg soybeans meal was mixed with 5.1 litres of water and dried in an electronic electric oven at the rate of 70 for 8 hours. After incubation dried meal was blended again into fine powder packed in plastic bags and stored at ambient temperature prior to use. Ingredients were mixed together at the right proportion to formulate 30% crude protein diet. Then phytase (enzymes) were added into each mixture at 0, 2000, 4000, 6000, 8000, and 10000 units phytase/kg diet. Each diet mixture was treated separately and extruded through a ¼ mm die mincer of Hobart A-200T pelleting machine (Hobart GmbH, Rben-Bosch, Offenbug, Germany) to form noodle-like strands, which were mechanically broken into suitable sizes for the O. niloticus fingerlings. The pellets were sun-dried, packed in labelled polythene bags and stored in a cool dry place to prevent fungal growth (Table 5).


Table 5 Gross composition of experimental diets

4.4 Biological evaluation
Mean weight gain = [final mean weight (g) – initial mean weight (g)]
Specific growth rate (SGR)=(Log Wf–Log Wi)×100/t (days)
Where, Log Wf = logarithm of the fish final weight gain.
Log Wi = logarithm of the fish initial weight, t = experimental period in days
Feed conversion ratio (FCR) = Feed intake (g)/ Weight gain (g)
Gross feed conversion efficiency (GFCE) = 1 / FCR × 100
Protein efficiency ratio (PER) = Wet body weight gain (g)/ Crude protein fed
Protein productive value (PPV) = (Final fish body protein - initial body protein)/ Crude protein intake × 100
Nitrogen metabolism (NM) = 0.549 x (Wi + Wf) t / 2
Where, Wi = Initial mean weight of fish, Wf = Final mean weight of fish, t = Experimental period in days, 0.549 = Metabolism factor
Apparent net protein utilization (ANPU) = P2 – P1 / PI × 100
Where: P1 = initial protein in fish carcass at the beginning of the experiment
P2 = final protein in fish carcass at the end of the experiment
PI = protein intake
4.5 Analytical methods
Toasted and incubated soybean meals, experimental diets and fish carcass were analyzed for proximate composition before and after the experiment according to the methods of A.O.A.C (2005).
4.6 Statistical analysis
Data resulting from the experiment was subjected to one-way analysis of variance (ANOVA) using SPSS (Statistical Package for Social Sciences 2006 version 15.0). Duncan multiple range test was used to compare differences among individual means.
Authors’ contributions
This work was carried out by two authors; OSE and NLC. Author NLC conceived the idea, NLC and OSE designed the study and wrote the protocol, author NLC supervised the study. Author OSE performed the experiment and the statistical analysis as well as managed the literature searches. Also, Author OSE wrote the first draft of the manuscript. All authors read and approved the final manuscript.
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