In Rizhao, Shandong province, China light shaded algae ponds model is creating an impact.
By Technical Support Team, Grobest Group Limited
Since 2012, in the northern part of China, the industrialised farming of turbot was badly impacted due to low market price, disease outbreaks and drop in groundwater levels. Later, as farmers shifted to sea cucumber farming, they also suffered the same fate. Consequently, some of these turbot and sea cucumber farmers decided to renovate their concreate ponds and switch over to industrial farming of the white-leg shrimp Penaeus vannamei.
After five to eight years of development, there are two common farming models: light shaded ponds with algae and dark shaded ponds using probiotics with water exchange. From our observation, such models have greatly contributed to farming success. In this article, we would like to focus on the basic infrastructure of these light shaded algae ponds.
Along the coast, south of Qingdao, the concrete ponds around Rizhao, Weifang and their vicinity are 5m x 5m and 6m x 6m square ponds. Going up north, around Haiyang, Zhushang and the vicinity, these ponds are larger at 10m x 10m and 20m x 20m. There are also smaller rectangular ponds of 3mx6m and 3m x 7m which have been developed following the sea cucumber ponds in Hebei, Tongying, Yingkou and Dalian areas.
Steel frames have been installed above these concrete ponds. In Rizhao and Haiyang areas, clean wrap films are used in two layers or in one layer with vinyl plastic. The overall structure resembles that of shading in a vegetable garden. While in Tongying and Hebei areas, polypropylene sheets are inserted between the steel structures, creating half-transparent dark shading.
Heating of pond water is by various ways: geothermal heat pumps, geothermal wells, gas turbines, biomass boilers as well as aluminum tubes in a central plate and steel with zinc coating. Coal-fired boilers have been phased out as a heating device.
These are achieved using roots blowers and nanotubes in the smaller ponds and paddlewheel aerators in bigger ponds. The target is optimal aeration of 4.0 ppm throughout the culture cycle.
Ideally, these should be circular in shape. Otherwise, it would be rectangular externally and circular internally, with a sludge pipe in the centre.
These vary with locations. In Shandong province, farms around Rizhao, Haiyang, Yentai and Weifang areas, use premium underground water at 10-25ppt salinity. Water is sand- filtered before channeling into the culture ponds. In normal, light shaded farms, the well water is sand filtered prior to use. In order not to disturb the shrimp, the water flow is controlled. Water is only added at 8 am to 3 pm. In the dark shaded ponds, the well water, after sand filtered is directed to boilers and flow into the ponds at 27~28°C.
Around Tongying in Hebei province, sea water is used. Usually there are outdoor disinfectant ponds of various sizes, from 1,300m2 to 3,300m2. Water is sand filtered and heated before flowing into the ponds. Since there is no temperature difference, there is no limit water exchange.
This is divided into phases; nursery and grow-out.
In the nursery, we start with post larvae (PL5) stocking at 5,000~10,000/m2. After 20 to 30 days, when the post larvae size reach 4,000PL/kg, we change ponds. The nursery management includes filling of water up to 60cm. Water is preheated, disinfected and enriched with probiotics before stocking. We only start feeding after the situation is stable.
This starts with water preparation and growing algae, mostly diatoms and chlorella, in light-shaded ponds; these are particularly important steps.
There are some critical issues. In terms of trace elements, there should be a balanced level of calcium, magnesium, and potassium. This is important during moulting and grow-out stages. Probiotics addition are timed with addition of water treatment products. It is also important to pay attention to the shape, colour, fine foams, stickiness of the water bubbles.
Key performance indicators
In a 6m x 6m ponds, stocking 400-600 PL/m2 and using a water exchange of 30-50% per day, we had achieved a survival rate of around 80%. The feed conversion ratio was 1.3. The final production yield was 8kg/m2. The key points for this super intensive farming model are using a good water source (either direct or through a reservoir) and maintaining optimal dissolved oxygen. An excellent drainage system to remove dead shrimp, faeces, etc. is important. Finally, this comes with optimal management practices throughout the cycle.
This article was published in September/October 2020, pp 16-18.