9 minute read
Production of tilapia with firm, tight-grained texture flesh
Specific diets change the characteristics of certain parts of the tilapia
By Nie Xiao Feng, Zhong Guo Xiong and Su Shi
Indoor greenhouse facilities (top) with recirculation water tanks (left) and water treatment system.
According to FAO, China produces 1.8 million tonnes of tilapia in 2016, ranking first in the world, with an export volume of 393,000 tonnes. Maoming is the main breeding area for tilapia in China and is known as the tilapia capital of China. At present, two species are mainly farmed: hybrid tilapia (Oreochromis mossambicus × O. niloticus) and Genetically Improved Farmed Tilapia (GIFT).
Through a direct introduction of Nile tilapia strains from four African countries (Egypt, Ghana, Kenya and Senegal) and four Nile tilapia strains that are more widely farmed in Asia (Israel, Singapore, Thailand and Taiwan), the GIFT tilapia was selectively bred by the International Center for Living Aquatic Resources Management (ICLARM, and now known as the WorldFish Center) and other institutions.
Flesh characteristics
The production of firm, tight-grained texture tilapia (known also as crispy tilapia) can be similarly compared to the production of the French foie gras where a specific diet changes the characteristics of goose liver. Why is there a market demand for firm, tight-grained texture tilapia in China?
The answer is because Chinese consumers are used to eating hot pot and cooking food in boiling water. Fish is also a common ingredient in hot pot dishes. However, traditional hot pot cooking mostly uses firm, tightgrained texture species such as grouper and snakehead. The flesh of tilapia and grass carp are rather soft that they quickly dissipate and no longer remain in one piece during the boiling process. Therefore, the firm, tightgrained texture tilapia flesh that remains as a solid piece during cooking has a wide market demand.
Transformation of tilapia flesh
The transformation of tilapia is made by adding broad beans or faba bean to the feed. Studies have shown that broad beans can induce an increase of reactive oxygen species (ROS) in the blood, which results in cell protein and lipid peroxidation. By reducing collagen transport, it leads to an increase in collagen accumulation, thereby promoting the formation of thicker interstitial muscle fibres.
Yu et al. (2017) reported that in the 1970s, fish farmers in Dongsheng Town, Guangdong Province, China, accidentally discovered that the muscle structure of grass carp changed significantly after they were fed only with faba bean (Vicia faba L.) and exhibited a significant increase in muscle hardness and crispiness, and thus became popular locally.
The difference between the muscle slices of ordinary grass carp and crispy carp was observed through a microscope and muscles of crispy carp showed a sturdier white texture with changes in the muscle fibre structural protein. The role of collagen is to produce good structure
connective tissues with mechanical properties, such as tensile strength, tension, elasticity, etc., to support and protect the body. This explains why the crispy carp is firmer and more elastic. In addition, crispy flesh has more fine fibres, which also means that the flesh is more tender. Compared with ordinary grass carp, the flesh quality of crispy carp has improved hardness, elasticity and cohesiveness.
Based on this principle, to create the firm, tight-grained texture of tilapia, feed in this project used broad bean flour as the main raw material. With the help of a Hinter company formulator, special tilapia feed was made with 31% protein content. The project lasted for two months and was completed in Maoming, China with Hinter technicians.
Farming system
In this project, we adopted a recirculating pond water culture model combined with water treatment system. The latter included two main treatment tanks - the brush sedimentation tank, and the bacterial biochemical tank. The brush tank mainly settled most of the remaining feed and faecal mucus and other solid matter, through a simple solid-liquid separation. The biochemical tank with a large number of bacteria groups was added to convert ammonia nitrogen and nitrite to improve water quality. The water finally flowed back into the fishpond. This study mainly focused on the feasibility and cost-effectiveness of landbased pond culture of crispy tilapia. Fish were fed twice a day in the morning and afternoon. Ammonia nitrogen and nitrite levels were kept low. Water loss was adequately replenished. The health condition of the tilapia was observed during feeding.
Table 1 shows the culture situation of tilapia fed over two months. Since tilapia were about 0.75kg at the start of the trial, by maintaining excellent water quality and a stable water temperature, the survival rate reached 98%. After two months of feeding, the growth rate of tilapia was 0.5kg per month, attaining a weight from 0.75kg to 1.75kg. Feed conversion ratio (FCR) was higher than in a traditional tilapia farming model. Unlike traditional pond culture which contains a lot of algae and insects for tilapia as food, this recirculating pond water culture model gave better FCR.
Compared to tilapia farmed in the traditional method, the flesh quality of the tilapia cultured in this recirculating pond water culture model was better and chewy, with less fishy taste. As can be seen in Figure 1, the crispy tilapia flesh on the left is more elastic. However, because the special feed production technology has not been fully mastered, there is still room for technology improvement. At present, based on all the information available, we are of the opinion that low temperature extrusion is a key step to prevent destruction of active ingredients in broad beans by high processing temperatures.
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Figure 1. Comparison of flesh quality between crispy tilapia (left) and regular tilapia (right)
Cost of production
In terms of costs, including feed, fish species, labour, water, electricity and heath treatments medicines, the cost to produce crispy tilapia is USD2/kg. The cost of feed will account for a 70% higher proportion than non-crispy tilapia feed. The selling price is around USD2.5-3.6/kg. At an average of USD 3/kg, the profit is USD1/kg. In contrast, the average profit for tilapia produced using a traditional system is USD 15 cents/kg.
Therefore, we conclude that the profit of crispy tilapia is relatively high. The profit/pond over a cycle can reach about USD460, which is suitable for farming in high-cost facilities such as recirculating pond system.
Judging from the anatomy of tilapia (Figure 2), after two months of feeding, the tilapia was generally healthy, with no bleeding or other abnormal external symptoms. The scales were neat and tight.
Tank area
24m2
Numbers
450
Density
19 tail /m2
Initial weight Days of Culture
0.75kg/pc 60 days Survival rate 98% Feed conversion ratio (FCR) 1.7 Final weight 1.75 kg/tail
Growth rate
0.5 kg/month
Viscera index
17.1%
Relative fatness
6.1
Cost Selling price Profit
USD2/kg USD3/kg USD1/kg
Table 1. Cost of production of a firm-texture tilapia in a recirculating pond water culture model
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However, there was mild enteritis (Figure 3). Stool drifting was also observed during feeding. According to some farmers visiting the facility, the crispy tilapia diet would cause digestive system problems, including enteritis or fatty liver. This may be related to the toxicity of broad beans. While on one hand, broad beans strengthen muscles, the ingredient also puts pressure on the intestines. Mixing of probiotics or digestive enzymes with feed may reduce the occurrence of digestive tract diseases. This needs to be verified by subsequent tests.
Tilapia is a hardy fish and is widely farmed all over the world. As a high value aquatic product, crispy tilapia combines its excellent breeding characteristics and raises its value to a new level through this special diet.
This recirculating pond water culture model can greatly reduce the risk of aquaculture. At the same time, the relatively large profits can make up for the cost of a large amount of infrastructure investment in the early stage. This is a culture model with strong degree of replicability and a promising future.
References
FAO. 2016. The state of world fisheries and aquaculture: Fish trade and commodities. Rome, Italy: FAO. Yuan, Y., Yuan, Y., Dai, Y., Zhang, Z., Gong, Y., & Yuan, Y. 2020. Technical efficiency of different farm sizes for tilapia farming in China. Aquaculture Research, 51(1), 307-315. Yu, E.M., Zhang, H.F., Li, Z. F., et al. 2017. Proteomic signature of muscle fibre hyperplasia in response to faba bean intake in grass carp[J]. Scientific Reports, 7:45950. Ye, X., Li, J., Lu, M., et al. 2011. Identification and molecular typing of Streptococcus agalactiae isolated from pond-cultured tilapia in China. Fisheries Science, 77(4):623-632. Yuan, Y., Yuan, Y., Dai, Y., et al. 2017. Economic profitability of tilapia farming in China. Aquaculture International, 25(3):12531264. Figure 2. Crispy tilapia. After two months of feeding, the tilapia was generally healthy, with no bleeding or other abnormal external symptoms and scales were neat and tight.
Figure 3. Inflammation of the front of the intestine due to mild enteritis
Xiao Feng Nie is Area Manager, based in Indonesia and has a few lines on responsibility. Email: niexiaofeng31@gmail.com
Zhong Guo Xiong is Sales Executive, based in Maoming, China
Su Shi is Sales Director, International Business Department, based in Vietnam. Email: susaquatic@gmail.com
All authors are with Guangdong Hinter Biotechnology Group Co., Ltd, China, a leader for the past 20 years in aquafeed premixes, additives, as well as R&D, production, marketing and integrated solutions for aquafeeds.
