Shrimp are sensitive to sudden changes in water salinity (salinity stress). This can lead to increased mortality, loss of appetite, cannibalism and increased susceptibility to infection. A frequent cause is heavy rainfall, which decreases the number of ions (e.g. calcium, magnesium) per litre of water and also affects water hardness (alkalinity).
Shrimp have natural mechanisms to cope with changes in water quality. Most of these mechanisms work well in the case of slow, long-term changes in salinity. However, they are easily overwhelmed by short-term changes in salinity that may occur within a few hours or even minutes. Once the salinity of the water drops below a certain level, the osmotic pressure leads to an influx of water into the tissue and consequently causes cell dysfunction and cell death.
In Southeast Asia, mortality rates ranging between 2 and 50 per cent have been reported after heavy rainfalls. This is not always evident, since cannibalism of the dead shrimp makes it difficult for farmers to assess the fatalities. Heavy rainfalls may also lead to long-term susceptibility to infection as well as problems in the moulting cycle, thereby ruining farm profitability and animal welfare. To avert such damage, shrimp farmers apply mostly technical measures to prevent pond flooding or to prepare for emergencies. But there is another way: preventing stress-related problems by using Anta®Ox Aqua to strengthen the animals against stress.
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Counter salinity stress with feed
Several authors investigated Anta®Ox Aqua as a fish feed additive that supports health, saves energy and strengthens shrimp against salinity stress. A supplementary scientific study was conducted by a specialised shrimp aquaculture laboratory (IMAQUA, Belgium). A rapid drop in salinity was simulated in a tank environment and the number of surviving shrimp was recorded over time. Before the salinity stress test, shrimp were administered different diets over a period of 35 days. The control group received no feed additive, while the diet of the treatment group included 800 ppm Anta®Ox Aqua.
During the feeding phase, the shrimp were kept in tanks with 70 individuals per tank and four replicates (tanks) per treatment group. Feed was administered six times per day. For the salinity stress test, 40 shrimp per group were transferred to a tank with water with low salinity to simulate a minus 20 ppt drop in salinity. The number of surviving shrimp was recorded every 20 minutes over a period of 360 minutes. The results are very promising (Figure 1). Shrimp receiving Anta®Ox Aqua in their feed survived significantly longer during the salinity stress test than shrimp in the untreated control group. This is particularly crucial because, even if the drop in salinity is not that great in actual fact, the environmental influences are cumulative and the animals will eventually experience stress.
Fig. 1: Survival curve of shrimp during the salinity stress test (drop of 20 ppt)
These test results demonstrate that Anta®Ox Aqua is an effective tool with which shrimp feed manufacturers can assist shrimp farmers in managing their animals’ health and welfare.
How can you and your customers best apply Anta®Ox Aqua? Contact our expert team to find out.