Aquaculture is the fastest growing food production sector in the world and fulfills half of the animal protein requirement. Commercial fish feed accounts for about 50-60% of the total operational cost of the production system. Owing to increase in demand and competition from other animal sectors with regard to the use of conventional feed ingredients, cost of important feed ingredients like fishmeal is increasing. Besides this, in the recent years, the declining trend of capture fisheries has further restricted the application of fishmeal in the fish feed formulations. One kg of farmed fish requires 0.7 kg of wild fish in the form of fishmeal as feed ingredients. This has prompted feed technologists to search and select sustainable non-conventional feed ingredients for the preparation of nutritionally rich and balanced formulated fish feed. These ingredients are gaining importance in the feed industry due to their reduced costs and their availability. One such locally available non-conventional feed ingredient is Palm Kernel Meal (PKM).

What is PKM?

Palm Kernel Meal (PKM) is an agricultural by-product of the oil palm (ElaeisguineensisJacq.) industry and is considered as an agro-industrial waste. It is produced from the kernels of the oil palm fruits, after the extraction of palm kernel oil either by mechanical or solvent extraction methods (Figure. 1). It is also called as palm kernel cake or palm kernel expeller. PKM resulting from mechanical extraction contains 5-12% oil and solvent-extracted palm kernel meal contains 0.5-3% oil.

Status of PKM production

About 80% of the PKM originates from Indonesia and Malaysia. Indonesia is the largest producer and exporter of palm oil and other palm oil by-products. In the year 2018, Indonesia produced 5.89 million metric tonnes of PKM and Malaysia produced 2.74 million metric tonnes of PKM. The other five main producer countries are Thailand, Nigeria, Colombia, Papua New Guinea and Guatemala. India is at 21st position with the total production of 0.01 million metric tonnes of PKM (USDA, 2019).

Nutritional profile of PKM

PKM is known as an energy-feed and also its chemical composition is similar to that of copra meal, rice bran or corn gluten feed. It is a highly fibrous and medium grade protein feed(Table. 1), hence most suited to ruminant or rabbit feeding.The wastes and residues from the palm oil extraction are cellulosic organic biomass with high nutrient content.

Table. 1. Chemical composition and nutritional value of PKM

Use of PKM in aquaculture

The use of PKM as a locally available non-conventional feed ingredient in the fish diets emerged in early 90’s. PKM had been substituted in the diet of tilapia and catfish fingerlings wherein, positive growth performancewas recorded at lowerinclusions levels.The following examples illustrate theinclusion levels of PKM in the diets for the effective performance of fingerlingsof different fish species (Table. 2).

Table. 2. Effective PKM inclusion level for fish fingerlings in the aqua-diets

Benefits of PKM in fish diets

The advantages of using PKM as a non-conventional feed ingredient in the fish feed are as follows:

• Globally, there is no competition for the consumption of PKM as a food product by humans.
• This meal is a cheap raw material source from palm oil industry and is a cost-effective one.
• It is also readily available as a feed ingredient for the fishes, poultry and ruminants.
• This is a waste or by-product from agriculture and/ processing industries that can be utilized effectively.
• The use of PKM as a fish feed ingredient plays an effective role in nutrient recycling and is an improved form of waste management.

Challenges for the use of PKM

Several factors limiting the incorporation of PKM into fish diets are:

• There is relatively low protein content in this meal, so there are also possible deficiencies of amino acids.
• The presence of anti-nutritional factors (non-starch polysaccharides) limits the direct use of PKM in the fish diets.
• It is slightly unpalatable and mixing this feed ingredient with palatable feedstuffs such as molasses will help improve intakes
• The higher fibre level can reduce the apparent digestibility for fish and other ruminants, limiting its inclusion in the feeds.

Ways to improve protein content in PKM

• Solid state fermentation- The protein content of PKM can be increased by the process of solid-state fermentation with cellulolytic fungus, Trichoderma koningii. Reports say that this process almost doubled the protein content of rawPKM, from about 17% to 32% crude protein.
• Amino acid supplementation- PKM is low in sulphur amino acids and probably lysine, which are essential amino acids necessary for the optimal growth of fish. Some studies have reported that amino acid supplementation (1-1.2 %) improved the growth of fish fed PKM based diets.
• Utilization of feed enzymes- The low digestibility of PKM is attributed to the high levels of non-starch polysaccharides (anti-nutritional factors)found in the cell wall. The use of proteolytic, fibrolytic or carbohydrate-degradingenzymes (ie., cellulase, xylanase) to PKM-based diets have great possibility of releasing unavailable nutrients and energy.
• Extrusion by Response Surface Method (RSM)- The high indigestible polysaccharides content present in the PKM limits the inclusion level in the diets of ruminants and fish. The twin-screw extrusion treatment of PKM helps to reduce the indigestible polysaccharides content during exposure to various temperatures, screw speeds, hopper speeds and moisture contents. Thus, a potential technological extrusion process resulted in reducing the anti-nutritional factors and improving the nutritive value of PKM (Roslanet al., 2017) as evidenced through an analysis using response surface methodology (RSM).

Status of research on PKM as a potential unconventional fish feed

The use of PKM as a locally available non-conventional aqua-feed ingredient emerged in early 90’s. Omoregie and Ogbemudia (1993) substituted PKM in the diet of Nile tilapia fingerlings and observed positive performance in the lower level of inclusion. Saad et al. (1997) found that fingerlings of O. niloticus showed significant sign of responses when fed with 30% inclusion rate. The fingerlings of Nile tilapia fed with African PKM (35%) in the practical diets gave better performances (Oliveira et al., 1997). Omoregie (2001) found that the minimum incorporation of PKM at 10% inclusion in the diet of Labeo senegalensis (African carp) juveniles had a reasonable feed utilization and nutrient digestibility.

According to Ng et al. (2002), the pretreated PKM diets using enzymes showed a considerable increase in the nutritive value. They found no better results in the fermentation (Trichoderma koningii) process and also reported that the raw PKM could be used as a dietary ingredient with no deleterious effects on red hybrid tilapia (Oreochromis sp.). A study on feeding trial was conducted in the practical diets for Red hybrid tilapia (Oreochromis sp.) containing the above meal which showed a better nutrient utilization efficiency in the partial (20%) substitution with soybean meal (Ng and Chong, 2002).

Ng and Chen (2002) observed that the performance of hybrid Asian–African catfish, Clarias macrocephalus × Clarias gariepinus decreased with increased inclusion of the PKM in the fingerlings diet. In the study performed by Iluyemi et al. (2010), it is reported that there were adverse effects on the performance and feed utilization of Red tilapia fed with fermented (Trichoderma longibrachiatum) meal. Udo et al. (2012) incorporated PKM as a plant-based feed ingredient in the reference diet of African catfish (C. gariepinus) fingerlings.

Among agro-industrial by-products (cassava meal, mesquite pod meal, cocoa meal), the diets prepared from PKM promoted the performance of Nile tilapia fish coupled with economic efficiency index (Carvalho et al., 2012). Thongprajukaew et al. (2015) studied the utilization of dietary modified palm kernel meal feed (water-soaked (SPKM), microwave-irradiated (MPKM), or water-soaked and microwave-irradiated palm kernel meals (SMPKM)) in the sex reversed Nile tilapia (Oreochromis niloticus) and observed that the SMPKM had improved the nutritional quality of PKM containing diet. The study conducted by Adjanke et al. (2016) showed that the acceptability and palatability response of O. niloticusfingerlings fed with the meal diets resulted in no significant differences among treatments. The incorporation of PKM in milkfish (Chanos chanos) diets high as 16.36% did not show any adverse effect on growth performance and gut health (Zulfahmi et al., 2019).

Conclusion

Availability and cost of conventional fish feed ingredients has become a major concern for the aquaculture feed industry. Therefore, use of non-conventional fish feed ingredients which are locally available at reduced cost can be a good option for the feed industry, especially for resource poor fish farmers. It can be therefore concluded that PKM is a viable non-conventional alternative feed ingredient and has a promising role to play in aquaculture. It presents an immense scope to substitute or replace fish meal either completely or partially post its processing augmented increase in percentage of protein. PKM can herald a new era in on-farm feed production for poor fish farmers and will provide an avenue for a more practical and cost-effective feed ingredient, adding to their overall profit.

References

Adjanke, A., Tona, K., Ble, C.M., Imorou Toko, I. and Gbeassor, M., (2016). Effect of dietary inclusion of palm kernel meal on feed intake, growth and body composition of Nile tilapia, Oreochromis niloticus reared in concrete tanks in Togo. International Journal of Fisheries and Aquatic Studies, 4(5): 642-646.

Alimon, A.R. and Wan Zahari, W.M., (2012). Recent advances in the utilization of oil palm by-products as animal feed. In International Conference on Livestock Production and Veterinary Technology (ICARD):211-218.

Carvalho, J.S.O., Azevedo, R.V.D., Ramos, A.P.D.S. and Braga, L.G.T., (2012). Agroindustrial byproducts in diets for Nile tilapia juveniles. Revista Brasileira de Zootecnia, 41(3): 479-484.

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Iluyemi, F.B., Hanafi, M.M., Radziah, O. and Kamarudin, M.S., (2010). Nutritional evaluation of fermented palm kernel cake using red tilapia. African Journal of biotechnology, 9(4).

Ng, W.K. and Chen, M.L., (2002). Replacement of soybean meal with palm kernel meal in practical diets for hybrid Asian-African catfish, Clarias macrocephalus× C. gariepinus. Journal of Applied Aquaculture, 12(4):67-76.

Ng, W.K. and Chong, K.K., (2002). The nutritive value of palm kernel and the effect of enzyme supplementation in practical diets for red hybrid tilapia (Oreochromis sp). Asian Fisheries Science, 15(2): 167-176.

Ng, W.K., (2003). The potential use of palm kernel meal in aquaculture feeds. Aquaculture Asia, 8(1): 38-39.

Ng, W.K., Lim, H.A., Lim, S.L. and Ibrahim, C.O., (2002). Nutritive value of palm kernel meal pretreated with enzyme or fermented with Trichoderma koningii (Oudemans) as a dietary ingredient for red hybrid tilapia (Oreochromis sp). Aquaculture Research, 33(15): 1199-1207.

Olvera-Novoa, M.A., Campos, S.G., Sabido, M.G. and Palacios, C.A.M., (1997). The use of alfalfa leaf protein concentrates as a protein source in diets for tilapia (Oreochromis mossambicus). Aquaculture, 90(3-4): 291-302.

Omoregie, E. and Ogbemudia, F.I., (1993). Effect of substituting fishmeal with palm kernel meal on growth and food utilization of the Nile tilapia, Oreochromis niloticus. Israeli Journal of Aquaculture, 45(3): 113-113.

Omoregie, E., (2001). Utilization and nutrient digestibility of mango seeds and palm kernel meal by juvenile Labeo senegalensis (Antheriniformes: Cyprinidae). Aquaculture Research, 32(9): 681-687.

Roslan, M.A.H., Abdullah, N., Murad, N.Z.A., Halmi, M.I.E., Idrus, Z. and Mustafa, S., (2017). Optimisation of extrusion for enhancing the nutritive value of palm kernel cake using response surface methodology. BioResources, 12(3):6679-6697.

Saad, C.R., Cheah, S.H. and Kamarudin, M.S., (1997). The use of palm kernel cake (PKC) in diets of red tilapia (Oreochromis niloticus). Universiti Putra Malaysia.

Thongprajukaew, K., Rodjaroen, S., Yoonram, K., Sornthong, P., Hutcha, N., Tantikitti, C. and Kovitvadhi, U., (2015). Effects of dietary modified palm kernel meal on growth, feed utilization, radical scavenging activity, carcass composition and muscle quality in sex reversed Nile tilapia (Oreochromis niloticus). Aquaculture, 439: 45-52.

Udo, I.U., Ekanem, S.B. and Ndome, C.B., (2012). Determination of optimum inclusion level of some plant and animal protein-rich feed ingredients in least-cost ration for African catfish (Clarias gariepinus) fingerlings using linear programming technique. International Journal of Oceanography and Marine Ecological System, 1(1): 24-35.

USDA., (2019). Palm kernel meal production by country in 1000 MT.

Zulfahmi, I., Herjayanto, M., Batubara, A.S., Affandi, R., Zulfahmi, I., Herjayanto, M., Batubara, A.S. and Affandi, R., (2019). Palm Kernel Meal as a Fish-feed Ingredient for Milkfish (Chanos chanos, Forskall 1755): Effect on Growth and Gut Health. Pakistan Journal of Nutrition, 18(8):753-760.