1. INTRODUCTION

Fish is a major source of protein, essential fatty acids and micronutrients [1–3]. It contributes to the production of diversified and healthy diets. Hence, during the recent year around the world, aquacultural and fish production gained high increase to supply the fish needs of the populations [4]. In Côte d'Ivoire, most of the fish farming production is dominated by Nile tilapia Oreochromis niloticus [5]. This fish has been raised in Côte d'Ivoire since the year 1940 for subsistence or commercial purposes; and the vast majority of fish farmers use the semi-intensive system in the earthen pond as rearing structures for O. niloticus production [5–8]. However, tilapia O. niloticus rearing on the majority of Côte d’Ivoire fish farms in a semi-intensive system meet various difficulties. Some of these problems are a long time (9–12 months) of merchant O. niloticus production; low weight (250–350 g) of fish farming tilapia, as well as low yields (1,000–6,000 kg/ha/year), recorded on the majority of fish farms reported by several authors [9–12]. Otherwise, the origins of these difficulties on the tilapia rearing are reported to be the inaccessibility of high-quality commercial feeds to the majority of fish farmers localized in the high concentration of fish farmers’ areas who are usually low-income farmers [5]. This situation results to the strong use of non-quality feed sellers’ commercial feeds; farm-made feeds; agro-industrial byproducts and non-conventional feeds to feed fish; non-respect of the feeding and rearing practices, thereby inducing low production of fish farming [11,12].

However, feeds are one of the major inputs in aquacultural production and the use of quality fish feeds in recommended quantity is the most important factor that determines the profitability and the sustainability of fish farms [13,14]. In the semi-intensive fish farming system, the tilapia merchant weight of 700 g and production yields of 15–17 tones/ha/year can be achieved with good nutrition practices [11,15,16]. According to Gabriel et al. [14] and Koumi et al. [8], the production of low-cost locally composed fish feeds, which take into account the requirement of different species and stages of farmed fish made with locally available raw materials with good processing methods, is the main challenge of fish farming. To try this solution, several authors tested with success the use of locally available ingredients in fish feeds [7,17–20].

In Côte d'Ivoire, the development of high-quality low-cost feeds for fish farmers has become a priority for many scientists. Previous works made by Bamba et al. [21,22] and Koumi et al. [23,24] on O. niloticus feeds, although based on local raw materials, were not specific to the areas of the high concentration of fish farmers. However, the different areas of fish farming practices in Côte d’Ivoire were well identified by [5] and availability and costs of raw materials vary by region and by area in the same country. In addition, the nutritional requirements of O. niloticus fingerlings are very well documented. The purpose of this study was to locally formulate low-cost quality feeds for O. niloticus juveniles in the three fish farming agroecological areas with accessible raw materials in each area to increase the availability of quality feeds for O. niloticus rearing in Côte d’Ivoire.

2. MATERIALS AND METHODS

2.2. Selection of Raw Materials and Feeds Formulation

The raw materials used in the formulation of feeds were selected based on their availability, market prices, and nutritional values by three fish farming agroecological areas. But for the same nutritional quality of several raw materials, availability and prices were the definitive selection criteria. So low-cost local fish meal at 42% of protein (0.52 USD/kg), copra (0.17 USD/kg), white rice bran (0.10 USD/kg), and soybean meal (0.70 USD/kg) were selected for Guinean area feed formulation; imported fish meal (1.21 USD/kg) with 55% of protein content, white rice bran (0.052 USD/kg) and soybean meal (0.64 USD/kg) were used for Sudano-Guinean area I; while local fish meal (0.52 USD/kg) content 42% protein, cottonseed oil cake (0.35 USD/kg), cornmeal (0.22 USD/kg), cashewnut oil cake (0.35 USD/kg), and soybean meal (0.73 USD/kg) were used for Sudano-Guinean area II feeds formulation (Table 2). Soybean meal available in the three agroecological areas and the two types of fish meals (42% and 55% of protein) were used as a protein source in feeds formulation (Table 3). White rice bran was used as a major source of carbohydrate in the Guinean and Sudano-Guinean I areas, and cornmeal was used as carbohydrate source of feed in the Sudano-Guinean I. Three isonitrogenous 30% protein feeds were formulated using linear programming method to quantify the different raw materials by feed (Table 4). All feedstuffs were incorporated following the limit levels recommended for fish feeds. Then, for each formulation, dry feed ingredients were weighed, ground in fine flour, and mixed and mixes were pelleted in 2-mm diameter pellets. Feeds were produced in bimonthly frequency to cover the needs of fish feeding. Samples of all the feeds produced were collected to the complete nutritional quality and analyzed according to [26,27].

Table 1: Côte d’Ivoire agroecological areas [25]. [Click here to view]

2.3. Fish and Feeding Trial

Juveniles males of tilapia O. niloticus were collected from a private fish farmer near Azaguié town (Latitude 5°–6 ° North; Longitude 4°–5° West) to constitute the three different groups of feeding trial. Three replicate earthen ponds were used by the feed formulated and feeding trial was performed on one fish farm located near Azaguié town, in Agboville Department localized in the south of Côte d'Ivoire to 40 km near Abidjan. Rearing was realized in the same conditions of fish farmers. Juveniles Nile tilapia O. niloticus of an average weight of 26.89 ± 2.98–27.35 ± 2.74 g were stocked at a density of 3 fish per square-meter and were hand-fed at 3%–5% body weight two times daily at 09:00 and 17:00 hours 6 days per week during 120 days. Earthen ponds water temperature, pH, dissolved oxygen, Total Dissolved Solids (TDS), Potential redox (ORP), and conductivity were monitored throughout the feeding trial. These parameters were measured weekly using multiparameter HANNA type. Every month, a sample of 30% fish was collected by the pond, individually weighed and measured. Then the monthly fish biomass by the pond was calculated based on the fish mean weight and the number of fish death recorded during the month for adjusting the feeding ration. At the end of the feeding trial, fish of each pond were harvested, counted, and individually weighed and measured. Total quantity of feed used was calculated for each pond.

Figure 1: Districts, Regions, Departments, and Subprefectures of fish farming practice in Côte d’Ivoire according to Yao et al. [5]. [Click here to view]

2.4. Determination of Growth and Feed Efficiency Parameters

Growth and feed utilization parameters were calculated using the following formulas according to [28]:

Weight gain: WG (g)

WG (g) = Final body weight of fish - Initial body weight of fish

Length gain: LG (cm)

LG (cm) = Final fish lenght - Initial fish lenght

Daily Weight Gain: DWG (g/day)

DWG ( g / day ) = Final weight of fish − Initial weight of fish Number of trial days

Daily Length Gain: DLG (cm/day)

DLG ( cm ) = Final fish length − Initial fish length Number of trial days

Specific Growth Rate: SGR (%/day)

SGR ( %/ day ) = Ln ( Final weight of fish − Ln ( Initial weight of fish ) Number of trial days × 100

Survival Rate: SR (%)

SR ( % ) = Final number of fish − Initial number of fish Initial number of fish × 100

Feed Conversion Ratio: FCR

FCR = Total weight of feed consumed by fish Wet fish biomass gain

Protein Efficiency Ratio: PER

PER = Wet fish biomass gain Total dietary protein in take

Table 2: Variation of the market price of raw materials selected by agroecological area. [Click here to view]

Table 3: Variation of proximate composition of raw materials selected by agroecological area. [Click here to view]

Table 4: Formulation (kg/100 kg) and costs of feeds produced for O. niloticus juveniles rearing by agroecological area (G = Guinean zone; Sudano-Guinean area I = SGI; Sudano-Guinean area II = SGII). [Click here to view]

3. RESULTS

3.3. Fish Growth and Feed Efficiency

Growth of O. niloticus juveniles fed with the different feeds is shown in Figure 2. Similar growth evolution trends were observed with the three groups of fish fed. Also, there was no significant difference (p > 0.05) in the monthly growth of the three groups of fish during the feeding trial. At the end of the growth trial, similar significant (p > 0.05) results were observed with all the parameters of growth performance and feed efficiency of O. niloticus juveniles analyzed. No significant difference was observed (p > 0.05) between all these parameters despite the differences observed between the means of values recorded (Table 7). Means weight gain values recorded for the three groups of O. niloticus fed with feeds produced varied between 134.62 ± 9.63 (SGII-30%) and 144.89 ± 7.25 g (G-30%) with daily weight gain oscillated between 1.12 ± 0.08 (SGII-30%) and 1.21 ± 0.06 g/day (G-30%). Survival rate recorded ranged between 99.44±0.00 (SGII-30%) and 100% (G-30%; SGI-30%). Feed conversion ratio values oscillated between 2.85 ± 0.14 (G-30%) and 2.88 ± 0.21 (SGII-30%) when protein efficiency ratio varied between 1.13 ± 0.08 (SGII-30%) and 1.17 ± 0.08 (G-30%).

Table 5: Proximate and mineral composition of feeds produced for O. niloticus juveniles rearing by agroecological area (G = Guinean area; Sudano-Guinean area I = SGI; Sudano-Guinean area II = SGII). [Click here to view]

Table 6: Physicochemical parameters values of the water in ponds during the feeding trial. [Click here to view]

4. DISCUSSION

All fish feeds produced were isoproteic at 30% protein level, but the difference between the compositions of feeds formulated depending on the availability, the cost, and the nutritional values of raw material used by area induced variations in feeds proximate composition. Using the fish meal, 42% protein at 30% in fish feed G-30% consequently influenced this feed moisture and carbohydrate levels and increased its ash, calcium, and phosphorus level compared to the other two feeds. High level of ash in fish meal used in feeds formulation influences the ash and mineral levels of the feed [29]. However, an excess of minerals and ash in fish feeds compared to the requirement value (<10) could be well released into the water by fish and should not affect the uptake of the other nutrient of feeds as reported by [29,30]. Also, high level of white rice bran incorporated in feed SGI-30% and the use of cashewnut oil cake in feed SGII-30%, both rich in the lipid at, respectively, 10.37% and 38.90%, consequently increased the levels of these feeds in lipid, carbohydrate, and gross energy compared to feeds G-30%. However, all feeds produced follow the needs of 30%–35% protein, 6%–10% lipid, inferior to 8%–10% fiber, and the minimum of 25% carbohydrate required for good growth of this stage (10–35 g) of O. niloticus juveniles reported by [31]. Also, the difference in price and quantity from the ingredients used for the three feeds formulated affected their cost. The lowest cost of feed recorded by feed G-30% could be due to the incorporating of 30% level of the low-cost local fish meal at 42% of protein, the good accessibility of copra, white rice bran and soybean meal in Guinean area, and its high level of industrialization compared to the two other areas.

Figure 2: Growth evolution of O. niloticus juveniles fed with feeds produced by fish farming agroecological area (Guinean zone; Sudano-Guinean area I = SG1; Sudano-Guinean area II) during 4 months. [Click here to view]

Nonetheless, the costs of these three formulated feeds of O. niloticus juveniles’ nutritional requirement that was adapted ranged between 0.43 and 0.52 USD/kg and were low compared to the costs of imported industrial commercial feeds (1.04–2.16 USD/kg) and were almost similar to industrial national commercial feeds (0.42–0.51 USD/kg) and the maximum costs of feeds sellers’ commercial feeds (0.52 USD/kg) and fish farmers’ feeds (0.47 USD/kg) met in Côte d’Ivoire [11]. So the costs of the three feeds proposed calculated from retail prices of raw materials selling on the market and/or by the feeds sellers’ feeds could be affordable for fish farmers in these three areas. Furthermore, the three simple composed feeds at 30% protein level had high nutritional quality than the feed sellers’ commercial feeds, the majority of fish farmers’ feeds and the agro-industrial byproduct used as fish feeds analyzed by [11]. Hence, the three feeds produced in this study offer the opportunity to improve availability and use of quality feeds for O. niloticus juveniles in the fish farming agroecological areas.

During the feeding trial, the water temperature of all the ponds ranged between 29.58 ± 1.22 and 29.92 ± 1.14oC and was revolved around 30oC reported as the optimal temperature of Tilapia Oreochromis niloticus rearing [32]. This resulted in advantage during the trial because the temperature is a control factor which plays a major role in fish metabolic regulation and can influence fish behavior and growth [33]. For high growth conditions of Tilapia O. niloticus in earthen ponds, [34] recommended a dissolved oxygen level ranged between 5 and 23 mg/l. In this study, dissolved oxygen values in ponds (8.05 ± 1.07–8.25 ± 1.56 mg/l) were within these reported values and show good oxygenation conditions of rearing ponds. Also, according to El-Sayed [35], O. niloticus can survive successfully and tolerate pH values recorded in these ponds (8.92 ± 0.88–9.62 ± 0.74) which oscillated between recommended values ranged between 4 and 11. Otherwise, according to Abowei [36], natural waters have conductivity ranged between 20 and 1500 us/cm. Conductivity values (19.43 ± 7.50–20.00 ± 8.49 µs/cm) recorded in all pond waters influenced by the levels of total solids dissolved levels (9.33 ± 3.01–10.50 ± 4.89) were within the conductivity values of natural waters (20–1500 us/cm). Similarly, the total solids dissolved values recorded in pond waters were under to the limit recommended at 500 mg/l [37]. In view of these comparisons, the degradation activities of organic matter and the mineral discharges from three feeds used by fish did not influence negatively the physicochemical characteristics of the water in the earthen ponds. In fact, all water physicochemical parameters data recorded showed the good growth conditions of O. niloticus juveniles during the feeding trial.

Table 7: Mean values of growth performance and feed efficiency parameters of juveniles O. niloticus fed with the feeds produced by fish farming agroecological area (Guinean zone; Sudano-Guinean area I = SG1; Sudano-Guinean area II) during 4 months. [Click here to view]

Table 8: Whole body composition of O. niloticus juveniles fed with feeds produced by fish farming agroecological area (Guinean zone; Sudano-Guinean area I = SG1; Sudano-Guinean area II) during 4 months. [Click here to view]

Growths of the three groups of O. niloticus juveniles fed with the feeds formulated were similar despite the significant difference observed in some nutritional parameters (moisture, lipid, fiber, ash, carbohydrate, gross energy, and protein/energy) of feeds. Also, values of feeds efficiency recorded during the feeding trial were not influenced by the quality of feeds, and, the survival rates at the end of the feeding trial were high (99.44% and 100%). These results proffer the opportunity to use low-cost local fish meal rich in ash as a protein source in juveniles O. niloticus feeds formulations. Likewise, cashewnut oil cake can be used as a lipid source and an additional protein and carbohydrate source in O. niloticus local quality feeds formulations. Similar growth results show also the opportunity of fish farmers to use the simply composed 30% protein fish feed with only three ingredients (SGI-30%) as high-quality feed for O. niloticus juveniles rearing.

Daily weight gain values recorded from O. niloticus fed with the formulated feeds (G-30%, SGI-30%, and SGII-30%), which ranged between 1.12 ± 0.08 and 1.21 ± 0.06 g/day, were higher than those obtained (0.35 ± 0.01g/d) by Oumer [38] with O. niloticus juveniles fed with 30% protein content feed in concrete ponds and further higher than those (0.89 g/d) of Opiyo et al. [39] recorded with the same fish fed in earthen ponds with 32.7% protein level of feed. Also, the daily weight gain values recorded with the feeds proposed in this study were higher than 0.86 ± 0.20 g/j reported by Sumagaysay-Chavoso [40] and were almost equal to the value of 1.5 g/d reported as reference growth value in intensive rearing system of O. niloticus juveniles by FAO [41]. In the same trend, specific growth rate values recorded in this study (1.48 ± 0.05–1.54 ± 0.03 %/d) were in the same order as those of 1.17 ± 0.06–1.49 ± 0.02 %/d reported by Abarike et al. [42] from O. niloticus fed with 30% protein in out-door hapas, and higher than 1.01 ± 0.02 and 1.25 ± 0.02 %/d recorded from the same fish by Opiyo et al. [39] with a commercial 32.7% protein level feed in earthen pond rearing during 6 months.

Concerning the efficiency of the feeds used, feed conversion ratio values recorded with fish fed with feeds produced varied between 2.85 ± 0.14 and 2.88 ± 0.21 and were similar to those (2.83–2.87) recorded by Ghozlan et al. [43,44] with juvenile O. niloticus fed with floating industrial commercial feed at 25% crude protein supplemented in vitamin and mineral premix during 6 months in the earthen ponds. Otherwise, feed conversion ratio (FCR) is an important indicator of the quality of fish feed, also, low FCR indicates better utilization of the fish feed [45]. Hence, the feeds conversion ratio values that recorded (2.85 ± 0.14–2.88 ± 0.21) lower or equal to 3 indicate the good use of all feeds by fish.

Compared results of daily weight gain, survival rate, specific growth rate, and feed conversion ratio with the previous research data show the competitiveness of these three feeds formulated at 30% protein level adapted to the O. niloticus juveniles rearing in the earthen ponds. These results could be due to the fact that these three feeds formulated at 30% protein proposed at low cost with the accessible raw materials in the three agroecological fish farming areas met well the essential nutritional needs for O. niloticus growth at this stage [29,31,46]. Results show the possibility of fish farmers in these areas to make simple composed feeds adapted to the growth of O. niloticus juveniles to improve growth and to reduce the time of merchant fish production. Results present also an opportunity to improve the availability of competitive quality fish feeds in the high concentration of fish farmers’ areas in Côte d’Ivoire.

Whole body protein composition of fish fed was not influenced by the quality of feed used. This result must be due to the fact that at O. niloticus, whole body protein composition is not affected by the proximate composition of feeds when feeds used are the same protein content [24,47]. The increase of crude lipid and gross energy from O. niloticus species with high levels of dietary lipid observed, it’s already well documented [25,48,49]. In fact, O. niloticus is unable to use dietary lipid and energy to improve feed efficiency and fish growth as observed from some catfish, so it accumulates dietary lipid in its carcass [50,51]. The similar ash levels recorded in whole body composition of O. niloticus independently to the feed used confirms the releasing of the excess of minerals and ash to feed G-30% into the water by fish.

5. CONCLUSION

The three composed feeds based on the available feedstuffs in three agroecological areas in Côte d’Ivoire were competitive to improve Oreochromis niloticus juveniles growth. Variation of raw materials used influenced biochemical composition of feeds formulated, but O. niloticus used these feeds for similar growth performance, feed utilization, and whole body protein content. These feeds proffer the opportunity to improve the availability of low-cost local quality feeds for O. niloticus juveniles rearing in the high concentration areas of fish farmers in Côte d’Ivoire.

ACKNOWLEDGMENTS

This work is a part of the framework of the PAFARCI (project to support the recovery of agricultural sectors in Côte d'Ivoire) project funded by the FIRCA (national inter-professional fund for research and agricultural council). Authors express their gratitude to the FIRCA and also thank feed sellers feeds and fish farmers for their help in this work. Authors also accord thanks to the Ivorian Association of Agronomic Sciences (AISA) for the good management of the funds for this project.

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