Ayesha Khizar & Mahroze Fatima
The aquaculture industry is the fastest-growing sector in food production, with an average annual production rate of 8.1%. Freshwater species play a great role and contribute almost 35% of aquaculture production. In Asia, especially in Pakistan, the most common and cultured species in polyculture system, among the Indian major carps, is Rohu (Labeo rohita), due to its nutritional value, delicious taste, affordability, and high market demand. As a result, it is intensively cultured with formulated feeds. Therefore, the formulation of cost-effective, nutritionally balanced feeds is crucial in the culture of this species, as feed procurement typically constitutes a substantial portion, ranging from 30% to 70% of operational costs in fish farming.
Fish meal (FM) has traditionally been the primary protein source in fish feed due to its well-balanced mineral, fatty acid, amino acid, and energy content. However, FM production faces limitations as wild fish stocks decline, which will lead to unavailability of FM in the market in near future. This scarcity of FM has created significant challenges for feed producers in the aquaculture industry. Consequently, the quest to identify alternative protein sources for aquafeeds is critical to ensure long-term sustainability. Therefore, nowadays, many research efforts are going on to identify the other alternative protein sources to replace FM.
In this regard, plant proteins (PP) sources are emerging as promising alternatives to FM, as they are abundant, cost-effective, and nutritionally valuable. The FM replacement with PP partially or totally does not compromise growth and fish quality. However, presence of anti-nutritional factors (ANFs) and amino acids deficiency make the use of PP limited and less effective. Thus, the seriously considered alternative source against FM is that which is less expensive as well as low in ANFs. Therefore, the rice protein concentrate (RPC) is a good and compatible PP source in this regard as compared to other plant sources and functions as FM replacer to a great extinct.
Rice is one of the most widely cultivated and consumed staple crops globally, in which Pakistan is one of the major rice-producing countries and Punjab is the largest contributor to rice with a 7.5 million tons’ production rate in 2019. The large-scale production of rice generates substantial by-products, such as rice bran and broken grains. In the aquafeed industry, the RPC has emerged as a promising and sustainable alternative ingredient. Derived from rice through protein extraction, RPC possesses several attractive characteristics, including its nutritional composition (lipid 11% and 75% crude protein), widespread availability, and potential environmental benefits. Besides these potential benefits, its use in aquafeeds is limited due to the presence of ANFs (phytate), and lysine deficiency.
Therefore, to overcome these, the lysine should be supplemented in the diet exogenously for the purpose of enhancing the use of RPC through amino acid balancing. The presence of phytate an ANF is another factor, which limits the use of RPC like other PP sources. Phytate combines with plant phosphorus and compromises its availability, it also forms complex with proteins and affects the digestibility and intake of PP. To overcome this limitation, exogenous enzymes like phytase are supplemented in PP-based fish diets to enhance nutrient digestibility. Phytase supplementation not only enhances digestibility but also increases feed utilization which ultimately lead to improved fish growth performance.
When the PP meals are used in fish feed for the longer duration it reduces the fish growth due to histological modifications in intestine, compromised amino acid metabolism, lowered enzyme activity, and down-regulation of the protein synthesis. Prebiotics that are non-digestible feed ingredients which selectively increase the metabolism and growth of positive gut bacteria, ultimately modulates the intestinal morphology and improves the gut health. In fish diet, prebiotics act as agents that convert nutrients in simpler compounds from the complex ones to be readily absorbed by the intestine and enhances the nutrient digestibility, growth, and feed efficiency. Xylooligosaccharide (XOS) is an emerging prebiotic in the aquaculture system, and can be formed after xylan hydrolysis. It increases the antioxidant status, growth performance, immunity, digestive enzymes, and feed utilization when fed to fish in their diet. However, there are only few studies reported which evaluate the effects of XOS on the intestine of aquatic animals. Thus, the effect of XOS supplementation in the fish diets having no FM is still not reported especially in most of the aquatic species. Hence, the main objective of the current study is to assess the ability of RPC to completely replace FM in the diet of rohu.
The research work was conducted in the Fish Seed Rearing Unit, Department of Fisheries and Aquaculture, University of Veterinary and Animal Sciences, Ravi Campus, Pattoki, under the supervision of Dr. Mahroze Fatima (HEC recognized Assistant Professor, Department of Fisheries and Aquaculture, University of Veterinary and Animal Sciences, Lahore, Pakistan), an expert in Fish Nutrition and Fish feed formulation. The whole study was based on three feeding experiments. The 1st experiment focused on assessing the impact of dietary phytase supplementation in the RPC based diets. Six experimental diets were formulated including positive control (FM-based diet having no phytase); FM0, negative control (RPC-based diet having no phytase); RPC0, and four phytase supplemental (250, 500, 1000 and 2000 FTU/Kg) levels. The results indicated significant improvements in growth, mineral and nutrient digestibility, digestive enzyme activities, serum biochemistry, and mineral deposition in rohu fingerlings. The optimal phytase level in RPC-based diets for rohu was determined to be 874.19 FTU/kg. In the 2nd experiment, the optimal phytase level from the first trial was utilized, and FM was replaced with RPC at varying levels (0, 25, 50, 75, and 100%) after lysine balancing. The results indicated that up to 50% of FM could be effectively replaced with RPC without compromising growth, nutrient digestibility, intestinal morphology, fatty acids and amino acids profiles, serum biochemistry, and digestive enzyme activity. This replacement was possible due to the incorporation of both phytase and lysine in the diet. In 3rd experiment, XOS a prebiotic was supplemented at 0, 0.5, 1 and 2% to the RPC based diets which remained unsuccessful in the replacement of FM. Eight diets with different RPC (75 & 100%) and XOS (0, 0.5, 1 and 2%) levels were formulated. The results revealed that 75% RPC diet efficiently replaced by fishmeal along with 1% XOS addition in rohu fingerlings without any negative effect on growth performance and intestinal health.
In conclusion, Rice protein concentrate serves as an efficient protein source. Their use in fish diet after phytase and lysine supplementation proves beneficial and replaced fishmeal up to 50%. Furthermore, the high levels of RPC could also be replaced when prebiotic was supplemented in the fish diet without causing any significant negative impact on fish growth and intestinal morphology, which ultimately benefits aquaculture sustainability.
The writers are PhD Scholars from the Department of Fisheries & Aquaculture, University of Veterinary and Animal Sciences, Lahore, Pakistan.