There is a need to increase biosecurity measures in the shrimp aquaculture industry as part of the 'new normal'. It is not a secret that the shrimp industry in many countries has suffered considerable economic losses due to a number of different shrimp diseases including the acute hepatopancreatic necrosis disease (AHPND). According to OIE, AHPND has been officially reported in China (2010), Vietnam (2010), Malaysia (2011), Thailand (2012), Mexico (2013) and the Philippines (2015) (NACA’s quarterly aquatic animal disease report, 2015 and OIE, 2013). The economic losses in the shrimp industry in Thailand alone is estimated to have cost the industry more than USD 5.01 billion to date (Shinn et al. 2016). There is no ‘silver bullet’ to address this disease or any future diseases. However, a combination of increased focus on biosecurity, adoption of better management practices and a focus on high quality nutrition and health products is showing promising results to get shrimp production back on track. This article summarises and discusses some of the initial results from introducing a shrimp nursery segment before the grow-out in Southeast Asia.
Shrimp diseases have caused serious economic losses to the shrimp industry globally. The initial weeks of shrimp production have always been of high importance, as getting the nutrition and health of the shrimp right at the early stages, will translate into a more robust animal later in the production. AHPND infects shrimp often during these critical first 30 days of production, thus hitting the shrimp industry hard.
AHPND is caused by a bacterium that colonises the shrimp gastrointestinal tract and produces a toxin that causes tissue destruction and dysfunction of the hepatopancreas, the shrimp digestive organ. The culprit is the bacterium Vibrio parahaemolyticus, as well as Vibrio harveyi, both common bacteria in brackish water. It affects the main species of cultured shrimp including the giant tiger shrimp Penaeus monodon, whiteleg shrimp Litopenaeus vannamei and also Chinese white shrimp Penaeus chinensis. With mortalities of infected shrimp stock often exceeding 70% this is a serious ‘game changer’ for the industry (OIE, 2016).
Farmers have tried to deal with the disease in different ways. Some of the approaches include lower stocking densities, change in water treatment, polyculture with tilapia and increased usage of antibiotics. Some of these changes in management procedures, especially the reintroduction of antibiotics in production, have led to problems further up the value chain. There is a clear correlation between outbreaks of AHPND and the number of detentions and rejections from shrimp importing countries (EU portal RASFF, 2016).
Figure 1. Examples of different levels of shrimp nurseries. Clockwise from top left: fibre glass tanks in a semi closed system with high level of aeration and water exchange, cement tanks in a semi closed system with high level of aeration and water exchange, and fully covered high level of aeration and water exchange.
Another approach is to introduce an additional production stage prior to stocking shrimp in grow-out ponds, namely the shrimp nursery phase. This is a practical management solution to deal with the disease. In the early days of shrimp farming in Southeast Asia, the use of nurseries was common practice, but the nurseries were phased out and direct stocking from hatchery to grow-out became the standard. In Latin America, the use of shrimp nurseries continued and developed further. This was done more as a management tool to increase growth of the shrimp and shorten the production cycle. In contrast, the recent reintroduction of shrimp nurseries in South-east Asia is more a measure of increased biosecurity, to protect against diseases in particular against AHPND.
The construction of nurseries can vary according to the level of production needed; knowledge and experience of the farmer as well as the level of investment the farmer has at his or her disposal. In Figure 1, we show some examples of shrimp nurseries; tanks in a semi closed system to high technology-high investment involving fully closed systems. One of the critical points is the transfer of the post larvae from nursery to grow-out. It is very important that this transfer is done as gentle as possible to minimise stress of the animals. Also at this stage e.g. 5 days before and 5 days after the transfer of the post larvae a high quality health booster additive or immune booster is given to help the post larvae with the transition.
The number of days the farmers keep the post larvae (PL10) in the nursery varies between 20-30 days. The additional days with better husbandry, higher quality diet and feed supplements in the nurseries are considered good protection against infections, especially with AHPND. This phase also increases the robustness of the shrimp towards other diseases.
Focus on high quality diet and feed Supplements
The approach used in shrimp hatcheries to focus on higher quality products in the early stages of the life cycle should be carried over into the shrimp nurseries. The opportunity to culture the shrimp in more controlled conditions also gives an opportunity for the farmers to take better care of the shrimp and to produce a more robust animal. This is very important and will ensure economic benefit at harvest.
In Table 1 the results from a commercial trial done in Thailand showed the difference between traditional feeding protocols for hatcheries compared to a high quality feeding protocol with high quality feed and addition of carefully selected marine protein sources and amino acid supplementation.
The numbers above indicate that there is a significant advantage from feeding post larvae at the nursery stage with high quality feed and health products with elevated doses of nutraceuticals and specific immunostimulants. The inclusion of these products ensure a diet with high levels of vitamins, lipids and nucleotides to support osmoregulation, growth and other vital processes during normal as well as stressful conditions. This all adds up into a stronger animal with a faster growth and improved survival.
Table 1. Key performance indicators from shrimp farms in Thailand, using normal feeding protocols developed for nursery conditions, compared to high quality nutrition and health additive protocol developed for nurseries. Post larvae were stocked in the nursery as PL10 and again transferred to the grow-out pond after 24 days in the nursery (PL34).
It is also important to note that stocking densities can be a lot higher if a high quality diet and additives are used. This makes it easier for the farmer to manage his water quality, water usage and also lower the initial investment needed as it saves space and infrastructure. The normal stocking densities in Latin America varies, but is often not more than 10-12 post larvae (PL)/L and with survival rates about 75-85%. In the trials done in Thailand the survival rates were 85-90% with stocking densities at 35-40 PL/L and some farmers are now experimenting with stocking densities at around 50 PL/L.
The increased levels of biosecurity that can be applied in a smaller water volume held in a tank or smaller pond, often in a building or under a roof are beneficial to the farmers as well (see Figure 1).
As an additional benefit the introduction of the nursery stage provides an extra point of quality control of the post larvae before stocking into the grow-out pond (Figure 2). This provides the farmers with opportunities to get their post larvae sampled and analysed for diseases before stocking to the grow-out pond. This can save the farmers a lot of work and potential economic losses.
Figure 2. A schematic diagram showing the additional disease testing opportunity to reduce the risk of introducing shrimp with disease in the grow-out pond.
Throughout the shrimp farming industry, there seems to be several areas to increase levels of biosecurity. Looking at livestock industries (poultry and pig production), where quarantine for visitors, disinfection procedures and movement of animals are a lot stricter than in any aquaculture industry. In aquaculture, there is still room for considerable improvements on biosecurity. As part of the new normal, the shrimp industry should learn from other industries in this aspect and increase levels of biosecurity at all production steps including hatcheries, nurseries and growout ponds.
The reintroduction of shrimp nurseries in many South-east Asian countries is an important step in managing the new normal for the shrimp industry. The emergence of new diseases will not stop and the industry has to adapt to current and future diseases through adapting management practices and focusing on quality feed and feed supplements to ensure robust animals. Shrimp nurseries are already being implemented on a commercial scale by farmers in Thailand, Vietnam and Indonesia. Not only industry but also governments in some countries see the importance in the introduction of nurseries. The government in Vietnam through the Directorate of Fisheries, sees the benefit for smallscale farmers using nurseries to increase production without increasing land use.
Farmers setting up shrimp nurseries should focus on using high quality diet and feed supplements that are specially designed to be used at this stage of shrimp production. There is an increased cost associated with this, but an increase in volume at harvest will more than recover the initial extra cost for using nurseries. Keep in mind that many farmers today do not make it past 30 days of culture due to disease.
Biosecurity is of crucial importance for the industry, both to deal with current diseases, and also to be ready for new and emerging diseases. We cannot predict what new diseases will be, but many of the critical control points and biosecurity measures are likely to target transmission routes of new diseases as well. In order to deal with the ‘new normal’ in shrimp farming, of which shrimp diseases will definitely be a part of, the industry needs to adopt biosecurity measures at farm level and to apply management practices that include a focus on quality feed and supplements.
This article was originally published in Aqua Culture Asia Pacific, 2016, Volume 12, Number 4.
1. EU portal RASFF 2016: Available at: http://ec.europa.eu/food/ safety/rasff/index_en.htm
2. NACA 2016: NACA’s quarterly aquatic animal disease report October –December 2015 (www.enaca.org).
3. OIE 2013: Technical Fact Sheet on Acute Hepatopancreatic Necrosis Disease: Aetiology Epidemiology Diagnosis Prevention and Control References.
4. Shinn et al. 2016: Counting the cost of aquatic disease in Asia in Aqua Culture Asia Pacific Jan/Feb Volume 12 Number 1 pages 14-18.