Research Article

Protein-Enriched Copra Meal as a Substitute for Soybean Meal in the Diet of Nile Tilapia (Oreochromis niloticus) Fry

Reginna Aivel Y. Rapiz-Cuzon1, Valeriano L. Corre Jr1, Rex Ferdinand M. Traifalgar1, Carmelo S. Del Castillo1,2*

1Institute of Aquaculture, College of Fisheries and Ocean Sciences, University of the Philippines Visayas, Miag-ao, Iloilo, Philippines; 2National Institute of Molecular Biology and Biotechnology, University of the Philippines Visayas, Miag-ao, Iloilo, Philippines.

Received | February 26, 2025; Accepted | May 17, 2025; Published | July 03, 2025

*Correspondence | Carmelo S. Del Castillo, Institute of Aquaculture, College of Fisheries and Ocean Sciences, University of the Philippines Visayas, Miag-ao, Iloilo, Philippines; Email: [email protected]

Citation | Rapiz-Cuzon RAY, Jr VLC, Traifalgar RFM, Castillo CSD (2025). Protein-enriched copra meal as a substitute for soybean meal in the diet of nile tilapia (Oreochromis niloticus) fry. J. Anim. Health Prod. 13(3): 642-648.

DOI | https://dx.doi.org/10.17582/journal.jahp/2025/13.3.642.648

ISSN (Online) | 2308-2801

Copyright: 2025 by the authors. Licensee ResearchersLinks Ltd, England, UK.

This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https://creativecommons.org/licenses/by/4.0/).

INTRODUCTION

Aquaculture plays an important role in ensuring global food security by providing a reliable source of protein and supporting livelihoods in many communities. Aquaculture may also assist in alleviating the pressure on wild fish populations, contributing to the conservation of marine ecosystems. By utilizing alternative food sources, such as plant-based proteins, aquaculture can further promote environmental conservation by reducing the reliance on overfished species and minimizing the ecological footprint of fish farming. In aquaculture, 50% of the production cost is accounted for by the capital costs of feed. As requirements for aquaculture feeds increase, shortages in primary feed ingredients have become a limiting factor in the sustainability of aquaculture (Hertrampf and Piedad-Pascual, 2000). To address these concerns, considerable research on fish nutrition has focused on finding and incorporating a cheaper plant-based protein source in the diet without compromising the nutritional availability (Wattanakul et al., 2021; Khan et al., 2013; Ogello et al., 2014; Tantikitti et al., 2005). Most of these studies investigated the potential of soybean meal (SBM) to replace fish meal in aquaculture feeds (Wu et al., 2021; Egerton et al., 2020; Yanti et al., 2019; Wang et al., 2016). Soybean meal (SBM) is generally utilized as the main plant-derived protein source for fulfilling the essential amino acid needs of commercially grown fish species (Alceste and Jory, 2000). However, its utilization in aquaculture is limited by its high cost, demand for human consumption, and its unpredictable supply as an import commodity in the Philippines due to competition with other agricultural industries (Plaipetch and Yakupitiyage, 2013; Intoy and Traifalgar, 2021). Copra meal, on the other hand, is readily available in mass quantities and cheaper than the imported SBM. The downside is that copra meal is known to be high in non-starch polysaccharides and low in protein as compared to SBM. The University of the Philippines Los Baños-National Institute of Molecular Biology and Biotechnology (BIOTECH-UPLB) recently developed a fermentation technology that converted copra meal into a Protein-Enriched Copra Meal (PECM®) with nutrient contents that are comparable to SBM. Though the nutritive components of this developed feed ingredient are supposedly adequate, its feed value has not been evaluated in most cultured aquatic animals. This study aims to evaluate whether PECM® can serve as an effective alternative to soybean meal in freshwater tilapia culture, determine its effect on fish growth and survival, and identify the optimal inclusion level in tilapia diets.

MATERIALS AND METHODS

Diet Preparation

Five formulated diets were prepared using different inclusion levels of PECM® replacing soybean oil by equivalent weight: Trt25 (25% PECM®), Trt50 (50% PECM®), Trt75 (75% PECM®), and Trt100 (100% PECM®) to substitute soybean meal. Trt0 (without PECM®) served as the control diet. Lipid sources used in the study included Danish fish oil and soybean oil (Table 1). All dry ingredients were ground and sieved to a 100 µm particle size. Sieved ingredients were mixed in a zipper storage bag, transferred to a basin, and liquid ingredients were then added. The ingredients were manually mixed until a clay-like consistency was achieved. The mixture was then processed in a pelletizer (Tasin TS-102AL) to form solid pellets. These pellets were arranged on a tray and oven-dried at 60°C for 24 hours. Once dried, the feeds were stored in a zipper storage bag at 4°C until use.

Proximate Analysis

The proximate composition of the formulated diets (Table 1) and the animal carcass were analyzed to determine how the dietary treatments influenced the carcass composition of cultured tilapia. Crude protein content was measured using the Kjeldahl Total Protein Nitrogen Method (Foss Tecator™ Digestion and Foss Kjeltec™ 8200 153 Auto Distillation). Crude lipid was analyzed using the Foss Soxtec™ 2050 Automatic System, following the Bligh and Dyer (1959) Method. Crude fiber was measured using the Ceramic Fiber Filter Method (AOAC, 1996). Ash content was determined gravimetrically by burning the sample in a muffle furnace at 600°C. Meanwhile, dry matter content was determined using the Mettler Toledo Halogen Moisture 158 Analyzer (AOAC, 1996). All analyses were conducted in triplicate.

 

Table 1: Dietary and proximate composition of Tilapia diets with different PECM inclusion levels (g/100 g).

Component	Treatment (g/100 g)
	Trt0	Trt25	Trt50	Trt75	Trt100
Sardine fish meal	16.00	16.00	16.00	16.00	16.00
Soybean meal	35.00	26.25	17.50	8.75	-
PECM	-	8.75	17.50	26.25	35.00
Rice Bran	15.00	15.00	15.00	15.00	15.00
Bread flour	23.00	23.00	23.00	23.00	23.00
Danish fish oil	4.00	4.00	4.00	4.00	4.00
Soybean oil	4.00	4.00	4.00	4.00	4.00
Vitamin	1.50	1.50	1.50	1.50	1.50
Mineral	1.50	1.50	1.50	1.50	1.50
TOTAL	100.00	100.00	100.00	100.00	100.00
Proximate analysis (%DM)
Crude Protein	30.18	30.22	30.25	30.29	30.32
Crude Lipid	12.70	12.45	12.20	11.94	11.69
Crude Fiber	4.95	4.53	4.11	3.69	3.27
Ash	6.97	6.43	5.89	5.34	4.80
NFE	45.20	46.37	47.55	48.74	49.92

 

Experimental Design and Feeding Trial

Nile tilapia (Oreochromis niloticus) obtained from SEAFDEC in Tigbauan, Iloilo, were raised at the Multi-Species Hatchery Complex under the management of the Institute of Aquaculture, College of Fisheries and Ocean Sciences, UP Visayas. Tilapia fingerlings (mean size: 0.47 ± 0.02 g) were randomly distributed in a 50 L rectangular tank with a stocking density of 20 individuals per tank. The tank assignment for each treatment was based on a completely randomized design (CRD) and was carried out in triplicates. Replacement fish were kept in a 1000 L tank with continuous aeration for seven days before starting the feeding trial. During the acclimation process, fish were fed with the control diet (Trt0). Siphoning of feces and excess feeds were done every morning. The feeding trial was carried out in a closed recirculating system with a mechanical filter operating at a flow rate of 50 mL per minute. Freshwater volume inside each tank of about 40 liters was maintained. The initial weight of the fish was taken after the acclimation period and dead individuals were replaced. The fish were hand-fed to satiation three times daily (0900, 1300, and 1600 h). Biomass sampling was conducted every 10 days, and the feeding rate was adjusted. Water change was done twice a week, by which about 50% of the water volume in each tank and 100% in the reservoir were replaced. Aeration was continuously supplied, and water quality was kept within the optimal range, with a temperature of 25-28°C, dissolved oxygen levels between 5-8 mg/L, a pH of 7-8, and salinity ranging from 0.02 to 0.04 g/L. Ammonia levels were monitored once a week (Molins-Legua et al., 2006): 0.04 ± 0.00 - 0.12 ± 0.01 ppm. At the end of the feeding trial, growth and feeding parameters, and survival of the fish were calculated using the following formulae (Traifalgar et al., 2010):

Statistical Analysis

The data gathered in the study were examined using IBM SPSS Version 26. A one-way ANOVA was conducted, followed by Tukey’s HSD post-hoc test, to identify significant differences (P < 0.05) between data sets.

RESULTS

Growth and Feeding Performance

After the 60-day feeding trial, growth performance, survival, and utilization of the provided feeds to O. niloticus fingerlings were determined. The growth performance of tilapia-fed diets containing different PECM inclusion levels is demonstrated in Table 2. R The results showed a significant difference (P < 0.05) between treatments in terms of growth performance indicators. Trt25 and Trt50 exhibited consistent results in regard to weight gain (%WG) (Figure 1) and specific growth rate (SGR), which did not exhibit significant difference from Trt0. A similar effect was also observed in feed utilization. The highest protein efficiency ratio (PER) value was recorded in Trt25 while Trt100 showed the significantly (P < 0.05) lowest value (Table 3). The feed conversion ratio (FCR) value of Trt100 was also significantly (P < 0.05) higher when compared to other treatments. Feed intake (FI), exhibited the same downward trend observed in Trt75 and Trt100. Survival rates were high across all treatments, and increased inclusion levels of PECM as a substitute for soybean meal had no adverse effects on the survival of cultured tilapia.

 

Table 2: Growth performance and survival of Nile Tilapia (Oreochromis niloticus) fed different treatments for 60 days.

Treatment	IBW	FBW	SGR (% d-1)	S (%)
Trt0	0.48 ± 0.07a	2.16 ± 0.37b	2.31 ± 0.20a	92.50 ± 2.89a
Trt25	0.59 ± 0.07a	2.34 ± 0.07c	2.29 ± 0.05a	98.33 ± 2.89a
Trt50	0.38 ± 0.07a	2.11 ± 0.68b	2.37 ± 0.11a	82.50 ± 9.57a
Trt75	0.50 ± 0.02a	1.46 ± 0.27ab	1.68 ± 0.04b	91.25 ± 6.29a
Trt100	0.42 ± 0.10a	1.08 ± 0.20a	1.23 ± 0.24c	87.50± 11.90a

 

Data represented as means ± SD. Means with the same superscripts are not significantly different (One-way ANOVA, Tukey’s HSD test, P > 0.05). BW (g), initial body weight; FBW (g), final body weight; SGR (% d-1), specific growth rate; S (%), survival rate.

 

 

Table 3: Feed utilization of Nile Tilapia (Oreochromis niloticus) fed different treatments for 60 days.

Treatment	FCR	FI (g/fish)	PER
Trt0	0.54 ± 0.03ab	0.91 ± 0.15b	6.15 ± 1.18ab
Trt25	0.40 ± 0.01a	1.07 ± 0.03b	8.24 ± 0.29b
Trt50	0.60± 0.08ab	0.98 ± 0.21b	5.84 ± 1.72ab
Trt75	0.59 ± 0.06ab	0.60 ± 0.13a	5.60 ± 1.10ab
Trt100	0.76 ± 0.21b	0.47 ± 0.04a	4.56 ± 1.21a

 

Data represented as means ± SD. Means with the same superscripts are not significantly different (One-way ANOVA, Tukey’s HSD test, P > 0.05). FCR, feed conversion ratio; FI (g/fish), feed intake; PER, protein efficiency ratio.

 

Carcass Composition

The carcass moisture content, crude protein, and crude lipid levels showed no significant differences among treatments suggesting that these were not influenced by elevated PECM® inclusion levels in the diet. However, the ash content was significantly (P < 0.05) different with Trt75 and Trt100 (Table 4).

 

Table 4: Carcass proximate composition of Nile Tilapia (Oreochromis niloticus) fed different treatments for 60 days.

Treatment	Moisture	Crude Protein	Crude Lipid	Ash
Trt0	70.34± 1.00a	61.83 ± 1.55a	6.94 ± 0.27a	5.34 ± 0.66ab
Trt25	70.42± 0.48a	62.50 ± 1.48a	6.92 ± 0.11a	5.02 ± 0.52ab
Trt50	70.45± 0.85a	62.81 ± 1.63a	6.92 ± 0.03a	5.88 ± 0.23ab
Trt75	70.45± 0.86a	62.92 ± 0.99a	6.98 ± 0.22a	6.03 ± 0.43b
Trt100	70.45± 0.87a	63.27 ± 1.63a	7.24 ± 0.14a	4.76 ± 0.35a

 

Data represented as means ± SD. Means with the same superscripts are not significantly different (One-way ANOVA, Tukey’s HSD test, P > 0.05).

 

DISCUSSION

This study demonstrates the feasibility of replacing soybean meal with Protein-Enriched Copra Meal (PECM®) at varying inclusion levels in the diet of Nile tilapia (O. niloticus). PECM® is made using a solid-state fermentation bio-processing system utilizing the fungus Aspergillus niger to improve the nutritive content of copra meal (Pham, 2017). Our results in the growth of the fish and utilization of the feed showed significant differences (P < 0.05) among dietary treatments. Tilapia exhibiting the highest %WG values were recorded in Trt25 and Trt50, indicating that soybean meal can be replaced with PECM® up to 50% (17.5% dietary inclusion) in a diet. This finding recommends that soybean meal, when combined with fermented copra meal in the diet, results in better growth. However, increasing the inclusion levels to 75% and 100% decreased the growth performance of the fish, suggesting that a total replacement of SBM with PECM® is not ideal. The apparent inhibition of growth at the higher dietary inclusion levels hints at the presence of anti-nutritional factors which can cause the unavailability of nutrients. This can limit the assimilation of nutrients, thus disenabling the attainment of optimum growth (Intoy and Traifalgar, 2021). Laining et al. (2017) reported similar studies showing that completely substituting soybean meal with fermented copra meal hinders rabbitfish growth and is not suitable for siganid diets, with only 13.7% inclusion being feasible. In milkfish, Chanos chanos, fermented copra meal was also incorporated in the diet (Apines-Amar et al., 2015) - at 5% inclusion level, this showed significant improvement of weight gain but at 20% inclusion, there was no significant difference to the control treatment. Further, its incorporation in the diet of Penaeus monodon (Apines-Amar et al., 2016) suggested that inclusion by as much as 40% did not affect feed efficiency, survival, and growth of the animal. In contrast, Mamauag et al. (2019) demonstrated the 100% replacement of SBM with FCM (16% dietary inclusion) upon supplementation of crystalline amino acids and this did not negatively affect the growth performance and digestive health of the grouper Epinephelus fuscoguttatus.

In the present study, the lowest FCR was also observed in Trt50, and values were significantly higher in treatments with elevated PECM® inclusion levels (Trt75 and Trt100). Significantly higher FI and PER values were also recorded in Trt50. In addition, a significant decline in feed utilization indices were consistently observed in Trt75 and Trt100. Most often, the high tannin concentration in copra meal, results in negative outcomes such as poor growth, feed utilization, and impaired feed palatability, this reduces feed efficiency and nutrient absorption. Due to its high fiber and anti-nutrient content, unprocessed copra inclusion levels in aquafeed are limited to 15% for omnivorous fish and 10% for carnivorous fish species (Obirikorang et al., 2016). Dileep et al. (2021) replaced fish meal in tilapia diet with a mixture of yeast fermented guar and copra meal. Findings of the study suggest that fermentation with yeast considerably improved the protein and amino acid content of guar and copra meal. Due to the presence of natural phytase enzymes and hydrolytic capacity of yeast, antinutritional factors (ANFs) such as saponin, tannin, trypsin inhibitor, and phytic acid showed a substantial drop in quantity following fermentation (Shiu et al., 2013; Greiner and Konietzny, 2006). The production of extracellular enzymes during yeast fermentation aids the synthesis of plant components and has also been highlighted in similar studies (Dawood and Koshio, 2020). However, Intoy and Traifalgar (2021) noted in their research that other components, including non-starch polysaccharides (NSP), may still be present in copra meal even after fermentation has removed major ANFs (Mukhopadhyay, 2000). This results in a decrease in the feed value of the plant ingredient (Sundu et al., 2009). Additionally, it has been demonstrated that raw copra meal contains 42.2% NSPs, which includes water-soluble galactomannans and water-insoluble mannan oligosaccharides (Knudsen, 1997). Galactomannan in the diets was associated with decreased feed utilization efficiency and growth retardation in tilapia (Hossain et al., 2003) and increased gastrointestinal viscosity which inhibits efficient nutrient absorption in carp (Hossain et al., 2001).

A decline in protein deposition in fish carcasses has often been observed in fish fed higher amounts of plant-based protein meals. However, in the present study, carcass proximate analysis showed that dietary treatments with PECM® inclusion did not significantly influence carcass composition. Similar findings were also observed in the grow-out culture of black tiger shrimp fed with fermented copra meal as a replacement for fish meal (Apines-Amar et al., 2019). In juvenile black tiger shrimp, a significant reduction in carcass protein was observed in a plant protein-based diet (PECM®: 10 g/100 g diet) with squid by-product hydrolysate as fish meal replacement (Pan and Traifalgar, 2022). No negative effects on carcass composition also supported the replacement of soybean meal with fermented palm kernel meal for sex-reversed red tilapia (Wattanakul et al., 2021), and soybean meal with fermented copra meal (FCM) for saline-tolerant Nile tilapia (Intoy and Traifalgar, 2021) but the highest replacement level resulted in decreased carcass protein content. The decline in growth performance and carcass protein content associated with increased inclusion levels of most plant protein components in fish diets has been linked to the imbalance profile and a lack of essential amino acids, which stimulate protein catabolism rather than anabolism (Lim and Lee, 2011). Tilapia is an omnivorous species, and the findings of this study indicate that its carcass composition, apart from ash content, remained unaffected by different PECM® inclusion levels. This suggests the species’ ability to tolerate high amounts of plant-based ingredients in its diet. Significantly higher value of ash content in carcass samples fed with Trt75 was observed. Intoy and Traifalgar (2021) also found that the ash content of tilapia carcass was significantly increased with elevated FCM inclusion. In contrast, carcass samples fed with Trt100 exhibited significantly lower ash content than the control. Magbanua and Ragaza (2022) reported that ash composition may be linked to the nutrient and mineral content of other feed materials, excluding the protein source. Furthermore, the survival rate of tilapia in this study remained unaffected by the varying levels of PECM® inclusion in the diet.

CONCLUSIONS AND RECOMMENDATIONS

The findings of this study indicate that Protein-Enriched Copra Meal (PECM®) performed best at a 25% inclusion level in the diet of Nile tilapia. However, replacing 50% of soybean meal with PECM® could be a more cost-effective option, as there were no notable differences in growth parameters among the control group, fish fed with 25% PECM®, and those receiving a 50% PECM® replacement. Dietary treatments in the present study compared favorably with soybean meal protein sourced diet in terms of growth, feed efficiency, and survival. PECM® can provide a sustainable and cost-effective source of feed protein since it is a cheaper and more readily available ingredient.

ACKNOWLEDGEMENTS

The authors extend their gratitude to the Department of Science and Technology (DOST) and the Philippine Council for Agriculture, Aquatic, and Natural Resources Research and Development (PCAARRD) for funding this research. We also appreciate the support of the University of the Philippines Visayas, College of Fisheries and Ocean Sciences, Institute of Aquaculture (UPV-CFOS-IA) for providing assistance and access to research facilities essential for the study’s analyses.

NOVELTY STATEMENTS

The study introduces Protein-Enriched Copra Meal (PECM®) as a novel plant-based protein source in tilapia nutrition, demonstrating its potential to replace up to 50% of soybean meal without compromising growth or health. This highlights PECM® as a practical alternative that supports sustainable aquaculture while addressing feed cost challenges.

AUTHOR’S CONTRIBUTIONS

VC designed the experimental study, culture facility, and feeding protocol of Nile Tilapia (Oreochromis niloticus). RT and CdC contributed to data analysis, interpretation, and manuscript preparation. RRC conducted the experiments proper; collected the data, conducted the initial result analysis, and drafted the manuscript.under the guidance of VC, CdC, and RT,. All listed authors contributed to the article and have given thumbs up to the submitted version.

Conflict of Interest

The authors have declared no conflict of interest.

REFERENCES

Alceste CC, Jory DE (2000). Tilapia - Alternative protein sources in tilapia feed formulation. Aquac. Mag., 26(4): 773-785.

Apines-Amar MJS, Andrino-Felarca KGS, Cadiz RE, Corre VL, Calpe AT (2016). Effects of partial replacement of fish meal by fermented copra meal on the growth and feed efficiency in black tiger shrimp Penaeus monodon. Isr. J. Aquacult. Bamid., 68: 1-6. https://doi.org/10.46989/001c.20837

Apines-Amar MJS, Coloso RM, Jaspe CJ, Salvilla JM, Amar-Murillo MNG, Saclauso CA (2015). Partial replacement of soybean meal with fermented copra meal in milkfish (Chanos chanos) diet. Aquac. Aquar. Conserv. Legis. Int. J. Bioflux Soc., 8(6):1019-1026.

Apines-Amar MJS, Felarca KGA, Libo-on JB, Corre VL Jr (2019). Fermented copra meal as replacement for dietary fish meal protein in grow-out culture of black tiger shrimp Penaeus monodon juveniles. Isr. J. Aquacult. Bamid., 71:1-8.

Association of Official Analytical Chemists (AOAC) (1996). Official Methods of Analysis of AOAC International. 15th ed. Vol. 1, Method 962.09, pp. 80–81. Washington D.C.: AOAC Int.,

Bligh EG, Dyer WJ (1959). A rapid method of total lipid extraction and purification. Can J Biochem Physiol. 37(8):911-917. doi: 10.1139/o59-099. PMID: 13671378.

Dawood MAO, Koshio S (2020). Application of fermentation strategy in aquafeed for sustainable aquaculture. Rev. Aquac., 12:987–1002. https://doi.org/10.1111/raq.12368

Dileep N, Pradhan C, Peter N, Kaippilly D, Sashidharan A, Sankar TV (2021). Nutritive value of guar and copra meal after fermentation with yeast Saccharomyces cerevisiae in the diet of Nile tilapia Oreochromis niloticus. Trop. Anim. Health Prod., 53(416): 1-13. https://doi.org/10.1007/s11250-021-02855-4

Egerton S, Wan A, Murphy K, Collins F, Ahern G, Sugrue I (2020). Replacing fishmeal with plant protein in Atlantic salmon (Salmo salar) diets by supplementation with fish protein hydrolysate. Sci. Rep., 10(1): 1-16. https://doi.org/10.1038/s41598-020-60325-7

Greiner R, Konietzny U (2006). Phytase for food application. Food Technol. Biotechnol., 44(2):125-140.

Hertrampf JW, Piedad-Pascual F (2000). Nutrition of Aquatic Animals at a Glance. In:Handbook on Ingredients for Aquaculture Feeds. Dordrecht: Kluwer Acad. Publ., 4-42 https://doi.org/10.1007/978-94-011-4018-8_2

Hossain MA, Focken U, Becker K (2001). Galactomannan-rich endosperm of Sesbania (Sesbania aculeata) seeds responsible for retardation of growth and feed utilisation in common carp Cyprinus carpio. Aquaculture, 203:121–132. https://doi.org/10.1016/S0044-8486(01)00617-2

Hossain MA, Focken U, Becker K (2003). Antinutritive effects of galactomannan-rich endosperm of Sesbania (Sesbania aculeata) seeds on growth and feed utilization in tilapia Oreochromis niloticus. Aquac. Res., 34:1171–1179. https://doi.org/10.1046/j.1365-2109.2003.00924.x

Intoy MMB, Traifalgar RFM (2021). Feed value of fermented copra meal as a sustainable feed ingredient in the diet of saline-tolerant Nile tilapia Oreochromis niloticus. J. Sustain. Sci. Manag., 16(8):28–43. https://doi.org/10.46754/jssm.2021.12.003

Khan MSK, Siddique MAM, Zamal H (2013). Replacement of fish meal by plant protein sources in Nile tilapia (Oreochromis niloticus) diet: growth performance and utilization. Iran. J. Fish. Sci., 12(4):855–863.

Knudsen KEB (1997). Carbohydrate and lignin contents of plant materials used in animal feeding. Anim. Feed Sci. Technol., 67: 319-338. https://doi.org/10.1016/S0377-8401(97)00009-6

Laining A, Usman U, Syah R (2017). Nutritive value of copra cake meal fermented with Rhizopus spp. and its use as a protein source in practical diets for rabbitfish (Siganus javus). J. Appl. Aquacult., 29(3–4):307–321. https://doi.org/10.1080/10454438.2017.1359726

Lim C, Yildirim-Aksoy M, Klesius P (2011). Lipid and fatty acid requirements of tilapias. N. Am. J. Aquacult., 73(2):188–193. https://doi.org/10.1080/15222055.2011.579032

Lim SJ, Lee KJ (2011). A microbial fermentation of soybean and cottonseed meal increases antioxidant activity and gossypol detoxification in diets for Nile tilapia Oreochromis niloticus. J. World Aquac. Soc., 42(4): 494-503. https://doi.org/10.1111/j.1749-7345.2011.00491.x

Magbanua TO, Ragaza JA (2022). Systematic review and meta-analysis of the growth performance and carcass composition of Nile tilapia (Oreochromis niloticus) fed dietary copra meal. Front. Sustain. Food Syst., 6(1025538):1-9. https://doi.org/10.3389/fsufs.2022.1025538

Mamauag REP, Ragaza JA, Nacionales T (2019). Fish performance, nutrient digestibilities, and hepatic and intestinal morphologies in grouper Epinephelus fuscoguttatus fed fermented copra meal. Aquac. Rep., 14(100202):1-6. https://doi.org/10.1016/j.aqrep.2019.100202

Molins-Legua C, Meseguer-Lloret S, Moliner-Martinez Y, Campíns-Falcó P (2006). A guide for selecting the most appropriate method for ammonium determination in water analysis. TrAC Trends Anal. Chem., 25(3):282–290. https://doi.org/10.1016/j.trac.2005.12.002

Mukhopadhyay N (2000). Improvement of quality of copra meal protein with supplemental amino acids in feeds for rohu Labeo rohita fingerlings. Acta Ichthyol. Piscat., 30(2):21-34. https://doi.org/10.3750/AIP2000.30.2.03

Obirikorang KA, Amisah S, Skov PV (2016). Growth performance, feed utilization and sensory characteristics of Nile tilapia Oreochromis niloticus fed diets with high inclusion levels of copra meal. J. Anim. Res. Nutr., 1(4:18):1-7. https://doi.org/10.21767/2572-5459.100018

Ogello EO, Munguti J, Sakakura Y, Hagiwara A (2014). Complete replacement of fish meal in the diet of Nile tilapia (Oreochromis niloticus) grow-out with alternative protein sources: a review. Int. J. Adv. Res., 2(8):962–978.

Pan MV, Traifalgar RFM (2022). Growth enhancing effects of squid by-product hydrolysate in plant protein-based diet fed to black tiger shrimp Penaeus monodon. Asian Fish. Sci., 35(1):56–67. https://doi.org/10.33997/j.afs.2022.35.1.005

Pham LJ (2017). A process of producing protein enriched copra meal as feed ingredient for the livestock and aquaculture industry. PH Patent No. PH1/2017/000081(A1),

Plaipetch P, Yakupitiyage A (2013). Effect of replacing soybean meal with yeast-fermented canola meal on growth and nutrient retention of Nile tilapia Oreochromis niloticus. Aquac. Res., 45:1744–1753. https://doi.org/10.1111/are.12119

Shiu YL, Wong SL, Guei WC, Shin YC, Liu CH (2013). Increase in the plant protein ratio in the diet of white shrimp Litopenaeus vannamei using Bacillus subtilis E20-fermented soybean meal as a replacement. Aquac. Res., 46(2):382–394 https://doi.org/10.1111/are.12186.

Sundu B, Kumar A, Dingle J (2009). Feeding value of copra meal for broilers. World Poult. Sci. J., 65(3):481–492. https://doi.org/10.1017/S0043933909000348

Tantikitti C (2014). Feed palatability and the alternative protein sources in shrimp feed. Songklanakarin J. Sci. Technol., 36(1):51–55.

Tantikitti C, Sangpong W, Chiavareesajja S (2005). Effects of defatted soybean protein levels on growth performance and nitrogen and phosphorus excretion in Asian seabass Lates calcarifer. Aquaculture, 248(1–4):41–50. https://doi.org/10.1016/j.aquaculture.2005.04.027

Traifalgar RF, Kira H, Thanh Tung H, Michael RF, Laining A, Yokoyama S (2010). Influence of dietary fucoidan supplementation on growth and immunological response of juvenile Marsupenaeus japonicus. J. World Aquac. Soc., 41:235–244. https://doi.org/10.1111/j.1749-7345.2010.00363.x

Wang Y, Yu S, Wang Y, Che J, Zhao L, Bu X, Yang Y (2016). Effect of replacing fish meal with soybean meal on growth, feed utilization and nitrogen and phosphorus excretion of juvenile Pseudobagrus ussuriensis. Aquac. Res., 47(10):3145–3155. https://doi.org/10.1111/are.12765

Wattanakul W, Thongprajukaew K, Hahor W, Suanyuk N (2021). Optimal replacement of soybean meal with fermented palm kernel meal as protein source in a fish meal–soybean meal–based diet of sex reversed red tilapia (Oreochromis niloticus × O. mossambicus). Animals (Basel), 11(2287):1-13. https://doi.org/10.3390/ani11082287

Wu Y, Wang Y, Ren X, Huang D, Si G, Chen J (2021). Replacement of fish meal with gamma-ray irradiated soybean meal in the diets of largemouth bass Micropterus salmoides. Aquac. Nutr., 27(4):977–985. https://doi.org/10.1111/anu.13239

Yanti M, Dewiyanti I, Nurfadhilah N, Nur FM, Batubara AS, Tahang M, Muchlisin ZA (2019). Replacement of fishmeal with soybean meal for the diet of seabass Lates calcarifer. IOP Conf. Ser. Earth Environ. Sci., 348(1):1-5. https://doi.org/10.1088/1755-1315/348/1/012105