Evaluation of production efficiency of Nile tilapia (Oreochromis niloticus L.) fed diets containing crop residues in combination with cocoa bean shell and coconut oil cake in Côte d’Ivoire

Y Bamba, N Ouattara¹, Y Soro¹, A Ouattara, K Yao¹ and G Gourène

Université Nangui Abrogoua, UFR-Sciences et Gestion de l’Environnement, Laboratoire d’Environnement et de Biologie Aquatique,
02 BP 801 Abidjan 02, Côte d’Ivoire
bamb_yacoub@yahoo.fr
¹ Université Nangui Abrogoua, UFR-Sciences de la Nature, Laboratoire de Biologie et de Cytologie Animale

Abstract

A 90-day feeding trial was conducted with Nile tilapia (Oreochromis niloticus) to assess the growth, body composition and cost–benefit. Tilapia juveniles weighing 4.35–4.38 g were grown in ponds and reared on an industrial commercial diet (as reference) and on two practical diets. Formulated diets were designated as CBS (cocoa bean shell, corn bran, soybean oil cake and cottonseeds oil cake) and COC (coconut oil cake, corn bran, soybean oil cake and cottonseeds oil cake). Three replicate ponds were randomly assigned to each of the three dietary treatments. Each diet contained approximately 28 % crude protein. Fish were fed twice daily (9.00h and 15.00h). The used stocking density was 15 fish/m².

The highest weight gain (44.7g) and the best feed conversion ratio (1.10) were obtained in fish fed diet CBS. The poorest weight gain (33.3 g) and the feed conversion ratio (1.41) were recorded for diet COC. However, tilapia fed diets COC and commercial feed displayed similar growth and feed efficiency patterns. Fat deposition was higher in fish reared on diets CBS and COC compared to the reference diet. Diets CBS and COC reduced the cost of feeding per unit of weight gain by 35.6 and 17.8 %, respectively.

Key words: agricultural by-products, fishmeal, plant protein, survival

Introduction

Aquafeed costs account for over 50-60 % of production costs due both to the limited supplies and increasing cost of fish meal (Hardy 2010). In response to the rising prices of fish meal, new alternative sources of protein that will allow the creation of suitable and inexpensive diets are being searched for various species of fish (González-Félix et al 2010; Abdel-Warith et al 2013). To reduce feed costs and the reliance on fish meal, plant feedstuffs appear to be one of the most appropriate alternative for fish meal in fish diets (El-Saidy and Gaber 2003; Hardy 2010; Slawski et al 2013). However, in tropical and subtropical regions, most of cereal and leguminous are keenly competed for direct consumption by humans and for industrial uses. Therefore, research efforts have been directed towards finding alternative sources of feed ingredients, using materials that cannot be directly consumed by humans (Bamba et al 2008).This approach may alleviate the competition between humans and animal, and reduce feed costs particularly for livestock species that are quite adapted for utilization of fibrous crop residues and by-products. Some of such materials are cocoa-bean shell, oil cakes, cereal bran and the like. They are potential dietary ingredients, owing to their availability, non-consumption by humans and nutritional value (NRC 2011). Cocoa bean shell has been reported to contain 13.2% - 17.7% crude protein and 13.0% -16.1% of fibre (Chung et al 2003). It has an intermediate buffer value between the protein and cereal sources of feed and could be utilized both as a medium protein and carbohydrate sources. However, cocoa shell has the disadvantage of containing 1.3% of theobromine and this limits its use for feeding purposes. Concerning the coconut oil cake, it is a good source of arginine and contains 18% - 23% crude protein. It is a valuable feed for herbivorous and omnivorous fishes (Sundu et al 2009). However, the factors which limit its incorporation at high levels are the presence of high amount of fibre and amino acid imbalance ( Mukhopadhyay 2000). Available knowledge shows that a sensible blend of different plant protein sources is needed to balance the indispensable amino acid profile (El-Saidy and Gaber 2003; Soltan and Fath El-Bab 2008; NRC 2011). Few studies have been conducted on the use of cocoa bean shell and coconut oil cake as supplemental feed ingredients for Nile tilapia. Furthermore, most studies focus on the nutritional characteristics of alternative protein sources rather than their ability to improve profit margins.

This study was designed to compare diets using corn bran, cottonseed oil cake and soybean oil cake in combination with cocoa bean shell and coconut oil cake on growth and production efficiency of Nile tilapia.

Materials and methods

Experimental diets and diet preparation

Formulations of the practical diets are shown in Table1.Two isoproteic practical diets (28 % crude protein) were formulated using soybean oil cake, cottonseeds oil cake, corn bran, cocoa bean shell, coconut oil cake and mix vegetable oil (palm and soybean oil). Soybean oil cake and cottonseeds oil cake served as the intact source of protein in all the practical diets supplemented with vitamin and mineral premix (2 % of premix) and sodium chloride (salt) (Table 1).

Corn bran, cocoa bean shell, vegetable oil and sodium chloride (salt) were purchased from local market. Vitamin and mineral premix, soybean oil cake, cottonseeds oil cake and coconut oil cake were obtained from a local feedstuffs company (Abidjan, Côte d’Ivoire).

Prior to the diet preparing, corn bran and cocoa bean shell were sun dried for about 7-8 hours at ambient air. Then, all ingredients were ground individually into fine particles (through 1 mm mesh) by using a locally fabricated hammer mill machine. Next, all the dietary dry ingredients with the exception of the mix oil, were transferred in one lot to a mixer machine (TOY: ECO 1150 L, 270 tr/mm, 2.2 kW) for 30 minutes mixing. The oil mix (1 %) was then added to the mixer mill slowly while mixing was still continuing. Each diet was produced in a one (1) ton capacity during every manufacturing. An industrial commercial gunpowder diet (1mm diameter) with 28 % crude protein served as reference. This diet was included in this feeding trial for a performance assessment of the experimental diets. All the three experimental diets were sealed in airtight bags.

Experimental design and procedures

The experiment was carried out at the “fish farm “Blondey, 25 km far away from Abidjan. For conducting the experiment, O. niloticus juveniles weighing 4.35–4.38 g were obtained from nursery ponds in our facilities. They were fed an industrial commercial diet (28 % crude protein) before the start of the feeding trial for 30 days. Prior to the start of the experiment, fish were counted, batch weighed and randomly distributed in nine earthen ponds of 400 m² at a density of 15 fish per square meter (15 fish/m²). All experimental fish were stocked in ponds under water-flow rate of 15 m³ /hour to maintain continuous aeration. Experimental ponds were supplied with water from a storage dam. Two practical diets designated as CBS and COC and an industrial commercial feed (reference) were used. Each diet was randomly assigned to triplicate groups. The diets were manually offered to respective group at 9.00, and 15.00 hours a day at a feeding rate of 5 % of body weight. Survival was determined daily by removing dead fish from each rearing pond. At monthly intervals, 25 % of the fish population in each pond was randomly sampled, batch weighed and data on weight gain and distributed feed recorded. Then, the daily feed rations (5 % of body weight) were adjusted accordingly. No feed was offered to the fish on the day they were weighed. The feeding experiment extended for 90 days. At the end of the feeding period, all experimental ponds were emptied and fish in each pond counted and batch weighed to determine fish weight and survival. Additionally, fifty (50) fish were randomly sampled per pond and individually weighed to evaluate treatment effects. Standard error of the mean (SEM) of final weight (FBW), weight gain (WG), specific growth rate (SGR), feed conversion ratio (FCR) and survival were determined and used as the indices to evaluate the growth performances.

Water quality management

Water from each dietary group was analyzed at weekly intervals in the morning (6.00 - 8.00 hours) and the afternoon (15.00 - 16.00 hours) for  temperature (Celsius thermometer), dissolved oxygen (oxygen meter, Model OXI 96), pH (pH-meter WTW, Model 95), conductivity (conductivity meter HACH, Model 44600) and transparency (Secchi disk).

Economic evaluation

The feed cost/kg diet and the feed cost needed to produce one kg of live weight gain of each experimental fish were estimated. The estimation of feed costs was based on local retail sale market price of all the dietary inputs at the time of the study. Each price is expressed in West African CFA franc (CFA: African Financial Community). An additional manufacturing cost  5000 F CFA/tonne and a transport expense (23000 F CFA/tonne) were taken in account.

Sampling and chemical analyses

At the beginning of the feeding trial, 20 fish were randomly sampled from the initial fish and killed for analysis of whole body composition. At the end of the 90-day experiment, 5 fish from each pond (15 fish per treatment) were randomly sampled for proximate analysis of whole body composition. Fish were sacrificed by lowering the body temperature in a freezer, ground into a homogeneous mass and stored frozen (-70°C) for carcass proximate analysis. Diets and fish samples were analyzed in triplicate for proximate composition. Crude protein, crude lipid, moisture and total ash were determined following standard methods (AOAC 2003). Dry matter was determined after drying in an oven at 105°C until constant weight; crude protein (N x 6.25) by Kjeldahl method after acid digestion; lipid by ether extraction using Soxhlet and ash content by incineration in a muffle furnace at 550°C for 24 h. Crude fibre content in diets was also determined following the standard methods (AOAC 2003) by acid-base digestion with details as described by Gul and Safdar (2009). Gross energy (GE) content was calculated using mean conversion values for protein (23.6 kJ/ g), lipids (39.8 kJ/ g) and carbohydrates (17.2 kJ/g) according to Jobling (1983). The digestible energy (DE) content was calculated using mean conversion values of gross energy for protein (23.6 kJ/ g), lipids (39.8 kJ/ g) and carbohydrates (17.2 kJ/g) and estimated digestibility values of 90 % for protein, 85 % for lipid and 50 % for carbohydrate (Jobling 1983). For essential amino acid analysis, experimental diets were analyzed by the Institute of Animal Husbandry and Genetics, Georg-August University of Gottingen (Germany). This analysis followed standard procedures of Naumann and Bassler (1976 - 1997) with laboratory details as described by Rodehutscord et al (2004). Table 2 displays the proximate composition and essential amino acid profile of commercial and formulated diets.

Calculation of nutritional and economical indices

The following parameters considered for the comparison among the treatments were calculated as follow:

Weight gain (WG, g) = (final weigh (g) - initial weight (g)); Daily weight gain (DWG, g/d) = (final weight (g) - initial weight) (g)/ feeding days; Survival rate (%) = 100 x (final fish number / initial fish number); Specific growth rate (SGR, % day^-1) = 100 × (Ln final weight - Ln initial weight)/ feeding days; Feed conversion ratio (FCR) = (dry feed given per fish) (g)/ (wet weight gain per fish) (g); Protein efficiency ratio (PER) = (wet weight gain per fish) (g) / (protein intake per fish) (g), Carbohydrate (Nitrogen free extract: NFE) = 100- (% moisture + % crude protein + % crude fat + % crude fibre + % ash); Gross energy (GE, kJ/g) = (23.6 kJ/g x % protein+ 39.8 kJ/g x % lipid+ 17.2 kJ/g x %carbohydrate); Digestible energy (DE, kJ/g) = [(23.6 kJ /g x % protein x 0.9) + (39.8 kJ/g x % lipid x 0.85) + (17.2 kJ/ g x % carbohydrate content x 0.5)] / 100 ; Reduction rate of cost per kilogram of diet compared with the reference diet (%) =100 x [(cost for reference diet – cost for practical diet) / (cost for reference diet)]; Diet cost per kg of weight gain = diet cost (F CFA kg_1) x FCR, where FCR is the feed conversion ratio; Reduction rate of diet cost per kg of weight gain compared with the reference diet (%.) =100 x [(diet cost per kg of weight gain for reference diet) – (diet cost per weight gain for practical diet)]/ (diet cost per kg of weight gain for reference diet).

Statistical analysis

Biological and analytical data were checked for normal distribution using the Kolmogorov–Smirnov Test. Fish growth performances, fish body composition and water quality variables were subjected to quadratic regression analysis (SPSS Inc., Chicago, IL, USA). Data were also subjected to one-way analysis of variance (ANOVA) using SPSS 17.0 for Windows (SPSS Inc). When differences among groups were identified, multiple comparisons among means were made using Tukey’s  test. Treatment effects were considered significant at P<0.05. Results are presented as means and standard error of means (SEM).

Results

Water quality

Water temperature ranged from 23.6 to 31.6°C, dissolved oxygen from 3.10 to 5.18 mg L^-1, pH from 6.32 to 9.11, conductivity from 40.9 to 70.2 μs/cm and transparency from 15 to 29 cm. There were no differences between treatment mean values. The range of mean values recorded for temperature (25,5- 25,8) , dissolved oxygen (3,10 - 3,64 mg/L), pH (6,80 -7,48), transparency (20,5 - 22,7 cm ) and conductivity (61,6 -63,3 μs/cm) were similar in all experimental units. These values were within the tolerant range of O. niloticus. Therefore, culture conditions were considered the same.

Growth performance and feed utilization

Growth performance in terms of final body weight (FBW), weight gain (WG), specific growth rate (SGR), feed conversion ratio (FCR), survival rate (%), protein efficiency ratio (PER) after 90-day feeding trial are presented in Table 3. At the beginning of the experiment, the initial body weight (IBW) of experimental fish ranged from 4.35 to 4.38 g. At the end of the growth trial, survival rates of juvenile tilapia for all treatments were over 93 % and there were no differences among dietary treatments.   Fish fed diet CBS had better growth performance than fish fed with the other diets.

The highest final body weight (FBW, 49 g) was recorded for the group fed diet CBS and the lowest FBW (37.7g) was observed in the fish fed diet COC. Likewise, the best weight gain (WG) (44.7g), specific growth rate (SGR) (2.69 %/day) and protein efficiency ratio (FER) (2.90) were observed in the fish fed diet CBS and the values were higher than those obtained for other groups. Fish in the dietary treatments COC and commercial had similar growth patterns. The feed conversion ratio (FCR)  ranged between 1.10 and 1.41. The best FCR (1.01) was found in diet CBS while the poorest (1.41) was obtained in diet COC.  

Economical evaluation of diets

Costs per kilogram experimental diets and feed costs per unit of weight gain are presented in Table 3. The results showed that costs per kilogram diet (costs/kg of diet) varied from 234 F CFA to 290 F CFA. The feed costs per unit of weight gain ranged from 258 F CFA to 400 F CFA. In terms of cost of the feed, the commercial diet (reference) was found to be the most expensive (290 F CFA /kg) and the diet COC was the cheapest 233 F CFA /kg). The diets CBS and COC represented approximately a 19 % cost savings compared with the commercial diet. The diets COC and CBS reduced the costs of feeding per unit of weight gain by 17.8 and 35.6 %, respectively compared with the commercial diet.

Proximate composition of whole body

After 90-day feeding, dry matter, total ash, crude protein and crude lipid contents of the whole body of fish in all the diet treatments increased compared with the initial status (Table 4). There were no differences were found in the dry matter, crude protein and ash contents among all the diet treatments. Lipid content showed a decreasing trend when fish were fed with the commercial diet.

Discussion

All the water quality parameters were within the acceptable ranges as recommended for tropical aquaculture (Boyd and Tucker 1998), and were similar in all experimental ponds. 

Similar high survival rates of tilapia while attempting to replace dietary fish meal with other protein sources were recorded by Gonzales et al (2007). Similarly, Bamba et al (2008) recorded 75 to 94 % survival after 90-day trial for Nile tilapia fed diets containing composite mixture of agricultural by-products. Likewise, González-Félix et al (2010) have reported a 90 to 100 % survival of O. niloticus. El-Saidy and Gaber (2003) reported SGR values ranging from 1.4 to 1.6 % day^-1 and FCR (from 1.9 to 2.1) when they replaced fish meal by a mixture of different plant protein sources in juvenile Nile tilapia diets. Soltant and Fath El-Bab (2008) replaced dietary fish meal by mixture of different plant protein sources in Nile tilapia diets and recorded SGR values ranging from 2.02 % day^-1 to 2.73 % day^-1. The feed conversion ratios (FCR) recorded in this study were comparable to values reported by Abdel-Warith et al (2013) ranging from 1.09 to 1.24 for O. niloticus fed with diets where fish meal was replaced by full-fat soybean meal, or by Bamba et al (2008), with FCR values ranging from 1.40 to 1.80 for O. niloticus fed with practical diets based on agricultural by-products. Our results are in accordance to the findings of other authors (El-Saidy and Gaber 2003; Gonzales et al 2007; Slawski et al 2013). For example, El-Saidy and Gaber (2003) substituted fish meal (FM) by a plant protein mixture (PPM) in diets of O. niloticus. They found that the partial or complete replacement of FM by PPM exhibited growth performance not differing significantly from the fish fed the control diet. Possible reasons for the inferior growth performance of the fish fed either commercial diet or diet COC compared to diet CBS might be attributed to essential amino acid imbalance (Dabrowski et al 2007) which could affect the digestion, absorption and metabolism. The dietary arginine and lysine requirements of Nile tilapia were determined to be 4.2 % and 5.12 % respectively (Santiago and Lovell 1988) with an optimal lysine/ arginine ratio calculated of 1.22 (Table 2). Based on essential amino acid (EAA) composition of experimental diets and EAA requirements of tilapia, the experimental diets COC and commercial were deficient in lysine, particularly, diet COC was most deficient (3.27 %). Besides, there were excess amounts of arginine in diets COC and the reference diet (9.57 and 8.34 %, respectively) than in diet CBS (6.75 %). The lysine/arginine ratio decreased from 0.77 in diet CBS to 0.34 in diet COC. Our result is in accordance to the finding of Berge et al (2002) who reported that the growth performance and feed conversion efficiency of Atlantic salmon actually increased in fish fed with diets marginal in arginine and supplemented with high levels of lysine. Based on information cited above, the amino acid imbalance in diets (lysine/arginine ratio) could be one of the most likely explanations of the difference in growth performance between the experimental diets. Similar results have also been found in Indian major carp (Abidi and Khan 2009) and in Cobia ( Rachycentron canadum) (Ren et al 2014). Other possible explanation for the highest growth performance observed in fish reared on diet CBS, might be due to the fact that, the tilapia received relatively high amount of lipid (7.13 %) in the diet (Table 2), because high dietary lipid content allows protein to be effectively utilized for fish growth. Similar protein-sparing effects of dietary lipid have been reported for Siganus rivulatus (Ghanawi et al 2011). Moreover, the highest dietary fibre content of treatment COC (14.7 %) might have contributed to lower digestibility of this diet than the other diets. Similar effect of dietary fibre was observed for the red drum (Sciaenops ocellatus), in which the digestibility of dry matter and energy decreased proportionally to the increase in fibre in plant sources (McGoogan and Reigh 1996). The low performance of fish fed diet COC compare to diet CBS suggests the low nutritional quality of coconut oil cake meal compared to cocoa bean shell, since this latter ingredient is considered deficient in lysine and contains high quantities of arginine and fibre (Saha 2003; Sundu et al 2009).

From the economic standpoint, the practical diets were found to be cheaper than the control (Table 3). They represented approximately a 19 % cost savings compared with the commercial diet. They also reduced feed costs per unit of weight gain of fish by rates of 35.6 and 17.8 %, respectively compared with the commercial diet. Our results are in agreement with those obtained by Coyle et al (2004) who reported a 20 % cost savings for diet without fish meal compared with the control diet.

The lower lipid content of the fish fed the commercial diet could be related to the dietary lipid content. It has been reported that an increase in dietary lipid leads to increased fat deposition in fish (Du et al 2005). Similar results were reported for Sarotherodon galilaeus (Goda et al 2007).

Conclusions

• This study demonstrated that cocoa bean shell, when used in combination with a mixture of plant proteins, is a suitable feed for use in tilapia diets.
  
  
•  Further research is required to determine the feasibility of improving the nutritional value of coconut oil cake and other available plant protein sources.

Acknowledgement  

Special appreciation goes to the Global Environment Facility (GEF) and the Nachhaltig Gegen Hunger, e.V, Germany (NGH) for supporting this research with their internally generated funds. Finally, the authors thank the readers of the journal who helped to correct the manuscript.

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Received 19 June 2014; Accepted 18 September 2014; Published 3 October 2014

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