by Li Hongpeng, Jian Linjiang and Dong Qiufen, Guangzhou Nutriera Group Co., Ltd, China

 

Large yellow croaker (Larimichthys crocea) is an important marine economic carnivorous fish, belonging to Perciformes, Sciaenidae and Pseudosciaena. It mainly distributes in the East China Sea and the Southern Yellow Sea, and a few in the offshore waters on the eastern side of the Leizhou Peninsula in the South China Sea, commonly known as large yellow croaker, the big king fish.

However, large yellow croakers were so severely depleted due to the heavy captureins in the 1950s and onwards. After peaking at about 200,000 tonnes in the mid-1970s, catches of the croaker in China declined by over 90 percent within two decades.Therefore, large yellow croaker was categorised as a 'threatened' fish in the IUCN Red List.

The extensive maricultural programmewas introduced to address food supply and control overfishing in the 1980s, particularly of the croaker and was one of the earliest for marine finfish, not only as a nation with rich and highly successful history in aquaculture in China, but globally.With the vigorous development of the cultured large yellow croaker industry in recent years, the aim of this paper is to make an in-depth study on the culture situation of large yellow croaker in China.

 

Large yellow croaker production in China

According to 2018 statistics, the total aquaculture production of large yellow croaker in 2017 reached 177,640 tonnes. The production in Fujian, Zhejiang,and Guangdongprovinces accounted for 84.75 percent, 8.21 percent, and 7.04 percentrespectively, as shown in table one.

Comparing withtheproduction in 2016, it showed a dramatic increaseof 17.54 percent in 2017. Due to the overfishing and low supply, the farming production increases sharply. In recent years, the consumption for valuable fishes are increasing with the living standard improving. As table2 shows, price of large yellow croaker kept stably high around USD $4/kg. It's estimated that the large yellow croaker production might continually rise in 2019.

Besides local consumption in mainland China, South Korea, Taiwanand Hong Kong of China are also major consumers for large yellow croaker.Some hatcheries in South Korea and Taiwanhave conducted trials of large yellow croaker breeding, but none of them have succeeded. Therefore, it mainly relies on the buying from mainland China to meet the local market demand.

South Korea is the largest importer of large yellow croaker and it imports about 40,000 tonnes of large yellow croaker from China every year. In recent years, Taiwanbuys about 8,000 tonnes of large yellow croaker from the Ningde area yearly, mainly with chilled products. Hong Kongbuys 3,000 tonnes of chilled large yellow croaker from Ningde annually. In addition, frozen large yellow croaker is also exported to the United States and European countries in a small amount.

 

Large yellow croaker culture mode

For large yellow croaker culture modes, there are mainly cage culture, pond culture. Currently, the most common culture is cage culture. Common cage sizes are 3×3metres (m), 4×4m, 5×5m, etc. Farmers usually use 4×4m cages, with a depth of four-to-eight metres(see figure one).

The cost of most common 4×4m cage is approximately$300-500 each. The specifications and mesh size of the cages are adjusted with the change of body length of the large yellow croaker, and the broken net will result in corresponding repair costs each year. There are several important factors in the cage culture, mainly sea area selection, manufacturing processes, setting methods and stocking density.

Among them, the factor of stocking density is most important. The stocking density of large yellow croaker is determined according to the smooth flow of water in the cage and the specifications. Suitable stocking density can increase both the yield and benefit. Too low stocking density of large yellow croaker cages will lead to an increase in the amount of residual bait, which will increase the cost and affect the growth environment of large yellow croaker. However, too high density will cause some large yellow croakers digestion problem and affect growth as well.

The common size of the culture cage is 4m×4m×4m, and the mesh size is usually between 20-60mm, which is adjusted according to the size of the fish body. Farmers usually connect several cages to increase the range of fish activity, there are fourcages, ninecages, and the largest has reached a recorded amount of 60 cages.

Large yellow croaker hastwo primarybreedingmonths,March and December. The large yellow croaker fries are placed in the cages after one-month nursery, commonly known as spring fries and autumn fries. The fry price is around $3 per 1,000 frys. The cost of fry only accounts for a very small part of the total aquaculture cost.

Large yellow croaker can be cultured and grown up to400 grams, which takes at least 17 months for them to grow to. Among them, the large yellow croaker has the fastest growth rate inNovember, December, and January.However, the growth rate is quite slow during the high temperature period.

If using trash fishes as foodduring whole process, the feed conversion ratio (FCR) is as high as eight with a high farming cost. Nowadays, more and more farmers turn to use commercial fish feed for this fish, and the FCR is around 1.9-2.0(see table 3). The survival rate of large yellow croakers cultured by different farmers is quite different. Due to the diseases, the mortality of large yellow croaker is generally higher, even more than 60 percent.

 

Large yellow croaker feed

The feed for large yellow croaker is generally trash fish and commercial feed. Trash fishneeds to be processed before being fed to the fish. A meat grinder generally cuts it into fish paste, or it is twisted into a meat emulsion and stirred to increase the viscosity, then squeezed into a block of different sizes by hand.

The trash fish has high protein content, and the farmers prefer trash fish as fresh bait, but it only provides minimal nutrition, and the quality of the trash fish on the market is variable. Some trashfish can also carry a large number of pathogenic bacteria, further infecting those fish fed the infected trash fish. Especially in summer, trash fish canfurther pollute the water and increase the probability of infection.

Farmers generally choose to use compound feed, because it consists of more comprehensive nutrient elements than the trash fish, and the pollution caused by feed sinking into the bottom of the water is much less than trash fish.The large yellow croaker compound feed is divided into two types: slow-sinking feed and floating feed, and crude protein normally ranges between40 percent and 50 percent(see figuretwo and figure three).

The price of trash fish in the surveyed area is around $0.5/kg, and itis normally higher in the closed fishing season. The price of compound feed is generally $1.3-1.9/kg. In order to encourage the farmers to use more commercial feed, the Chinese government subsidises farmers to use commercial feed.

In the hatchery and nursery stage, farmers prefer to use slow-sinking feed due to the habitus of large yellow croaker living in bottom layer. Farmers would start using floating feed in growing stage due to easy observation of the feed intake condition.

 

Functional feed

The major diseases for large yellow croaker are parasites, white spot disease and white gill. The peak disease season is July and August. At present, it was confirmed that the large yellow croaker's white gill is a viral disease and there is still no particularly good treatment in medicine to cure it. As the biggest aquatic solutions supplier in China, Guangzhou Nutriera Biotechnology Co., Ltd has a technical service team to help the farmers for health & sustainable fish farming management.

Nutriera also has helped some feed mills to produce functional fish feed, which could improve the profit by improving the fish immunity and health to decrease the chance of getting disease (see figure four and figure five).

Functional feed can increase the feed attracting and growth promoting(see figure six). It could enhance fish immunity against disease. Functional feed demonstrates strong advantages by adding natural plant extracts and immunoregulatory factors. It could be a trend in using functional feed to improve fish growth and immunity in the future.

 

Outlook

Large yellow croaker is a characteristic marine aquaculture species in China. Its development has driven many related industries and gradually occupied an important position in the marine aquaculture industry. More research on this fish is continually being carried out by the support of China-ASEAN Fisheries Resource Conservation and Expoloitation Fund and the government also tries to increase financial, technical, and other supports to promote the sustainable and healthy development of the large yellow croaker culture industry.

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