對蝦養殖的棘手難題科普實踐

對蝦養(yang) 殖的棘手難題

Collaboration article with Stony_Brook

對蝦是一種美味的高蛋白海鮮，養(yang) 殖規模大，在甲殼類水產(chan) 養(yang) 殖中占據首要地位，也備受消費者的喜愛。凡納濱對蝦（Penaeus vannamei）、羅氏沼蝦（Macrobrachium rosenbergii）和斑節對蝦（Penaeus monodon）是世界範圍內(nei) 產(chan) 量最高的三種優(you) 質對蝦。其中，凡納濱對蝦富含蛋白質、礦物質和不飽和脂肪酸，並且含有多種對人體(ti) 有益的生物活性成分，是一種質量優(you) 良、營養(yang) 均衡的食源性營養(yang) 源。因此，凡納濱對蝦在保健品、醫藥、化妝品、食品添加劑以及水產(chan) 養(yang) 殖等方麵都具有廣闊的應用前景，有較高的經濟價(jia) 值和醫用價(jia) 值。

Shrimp, a delicious seafood high in protein, currently plays a leading role in crustacean aquaculture production with a fast-growing market and farming size. Penaeus vannamei, Macrobrachium rosenbergii, and Penaeus monodon are known as the three best-quality shrimps with the highest production rates in the world.Penaeus vannamei in particular, is especially rich in proteins, minerals, unsaturated fatty acids, and contains functional biological components that have various beneficial effects for the human body. Overally, it is a high-quality and balanced source of nutrition. Therefore, this kind of shrimp has broad applications in health products, medicine, cosmetics, food additives, and aquaculture, and has a high economic and medicinal value.

凡納濱對蝦還具有生長速度快，抗病能力強，易粗養(yang) 易運輸以及產(chan) 肉量高等優(you) 點。隨著中國經濟的發展和人民生活水平的提高，目前的對蝦產(chan) 量已不能滿足快速增長的市場需求。凡納濱對蝦的產(chan) 量和養(yang) 殖規模在中國蝦蟹類人工養(yang) 殖業(ye) 中均居首位。根據《中國漁業(ye) 統計年鑒》的數據，在2013年至2020年間，中國對蝦產(chan) 量總體(ti) 呈上升趨勢，到2020年達到630.73萬(wan) 噸。目前全球對蝦產(chan) 量超過800萬(wan) 噸，由此可見，在中國乃至全世界，對蝦已經成為(wei) 一種交易量很大的海鮮。

Penaeus vannamei has the advantages of fast growth, strong disease resistance, easy rough culture and transportation, and high meat yield. With the development of China's economy and the improvement of people's living standards, the current yield of shrimp is unable to satisfy the fast-growing market demand. Among the artificially cultured shrimp and crabs in China, the yield and culture of Penaeus vannamei rank first. According to the data from China Fishery Statistical Yearbook, Chinese shrimp production showed an overall upward trend from 2013 to 2020, reaching 6.3073 million tons (MT) by 2020, while the whole world currently exceeds 8 MT of high value. This proves that shrimp has emerged as a highly traded seafood product in China and around the world.  

水產(chan) 養(yang) 殖業(ye) 在亞(ya) 洲甚至是全球水產(chan) 行業(ye) 中占據主導地位，但目前正麵臨(lin) 著嚴(yan) 峻的考驗。據世界糧農(nong) 組織估計，由疾病造成的經濟損失每年超過90億(yi) 美元，約達世界魚類和貝類養(yang) 殖行業(ye) 產(chan) 值的15%。疾病的威脅不僅(jin) 阻礙許多水產(chan) 養(yang) 殖業(ye) 的發展，甚至導致一些養(yang) 殖企業(ye) 倒閉。一些國家的對蝦產(chan) 業(ye) 也因病害而遭受重創。

Aquaculture dominates aquatic food production both in Asia and globally, and is now facing a significant challenge. In this industry, economic losses due to disease outbreaks have been estimated by the Food and Agriculture Organization (FAO) to be over $9 billion per year, which is approximately 15% of the world's farmed fish and shellfish production value. The threat of disease has become a barrier that prevents numerous aquaculture industries from developing, and has even led to the collapse of some. Because of this, shrimp production has been seriously damaged in several countries.

例如對蝦急性肝胰腺壞死病（AHPND），最初被稱為(wei) 早期死亡綜合征（EMS），對對蝦養(yang) 殖業(ye) 就造成了毀滅性的打擊。這種疾病發病快，從(cong) 放養(yang) 後約8天開始傳(chuan) 染，在20-30天內(nei) 對蝦出現大量死亡（死亡率高達100%）。據估計，疾病死亡率每增加1%，經濟損失每公頃增加25.5美元，損失概率增加1.4%。

Acute hepatopancreatic necrosis disease (AHPND), originally known as early mortality syndrome (EMS), has a devastating impact on the shrimp aquaculture industry. This disease develops quickly, starting about 8 days post-stocking, with severe mortalities (up to 100%), occurring within 20-30 days. It is estimated that these losses raised prices by $25.5 per hectare, and loss probability raised 1.4% for every 1% increase in disease mortality. 

對蝦急性肝胰腺壞死病自2009年首次暴發以來，迅速在世界各地蔓延，不僅(jin) 導致對蝦大量死亡，給對蝦養(yang) 殖業(ye) 造成嚴(yan) 重經濟損失，也對食品安全構成了威脅。自2013年底南亞(ya) 國家的養(yang) 殖行業(ye) 崩潰以來，該疾病危險性不斷升級。在2017年，世界動物衛生組織（OIE）通過了修正提案，在《水產(chan) 守則》和《養(yang) 殖指南》中為(wei) 該疾病設立了專(zhuan) 門的章節，進一步強調了該疾病的嚴(yan) 重性。

Since the outbreak in 2009, AHPND has spread rapidly around the world, causing massive shrimp mortality and severe economic losses to the shrimp farming industry, as well as posing a threat to food safety. Moreover, it escalated in late 2013, when the industry collapsed in South Asian countries. In 2017, the World Organization for Animal Health (OIE) adopted amendments to create a specific chapter in both the Aquatic Code and Manual for AHPND, which demonstrates that the authorities have acknowledged its seriousness.

對蝦急性肝胰腺壞死病的主要病原是一種攜帶pVA1質粒的副溶血性弧菌（Vibrio parahaemolyticus），該質粒編碼靶向蝦的肝胰腺細胞的PirA和PirB二元毒素。這些毒素會(hui) 結合對蝦的肝胰腺上皮組織並造成穿孔，最終導致細胞的死亡。

The major pathogen of AHPND is Vibrio parahaemolyticus which carries a unique plasmid, pVA1. The plasmid encodes the binary PirA and PirB toxins which target the digestive gland of shrimp. These toxins bind with hepatopancreatic epithelial tissue, forming pores and leading to subsequent cell death.

pVA1質粒可從(cong) 副溶血性弧菌轉移到其他菌種，如朋氏弧菌（V. punensis）、哈維氏弧菌（V. harveyi）、歐氏弧菌（V. owensii）、坎貝氏弧菌（V. campbelli）、希瓦氏杆菌（Shewanella sp.）等，這使宿主病菌具有更強的致病能力。致病菌傳(chuan) 播後會(hui) 定居在對蝦的消化道內(nei) ，對組織造成嚴(yan) 重破壞。感染AHPND的對蝦的主要臨(lin) 床症狀是食欲減退、嗜睡、生長緩慢、外殼軟化和空腸。由於(yu) AHPND的發展迅速，一旦發病，就將導致無法挽回的大規模對蝦急性死亡。

The pVA1-type plasmid can also be transferred from V. parahaemolyticus to another species, such as V. punensis, V. harveyi, V. owensii, V. campbelli, and Shewanella sp., giving the host bacteria a stronger pathogenic ability. The bacteria then spread and colonize the shrimp's digestive tract, causing severe damage to tissues. Moreover, the primary clinical AHPND symptoms in infected shrimps are anorexia, lethargy, slow growth, soft shelling, and empty digestive tract. Due to the rapid development of AHPND, once the disease occurs, it will cause an irreparable large-scale acute shrimp death.

傳(chuan) 統AHPND的防治方法存在收效甚微或者治療效果不可持續的缺點。例如，將抗生素添加進對蝦飼料或養(yang) 殖水體(ti) 中是對抗對蝦細菌感染的有效方法之一，但使用抗生素會(hui) 對公眾(zhong) 健康和環境構成嚴(yan) 重威脅。在對蝦養(yang) 殖場中，抗生素的持續使用將促進抗生素耐藥細菌（ARB）菌株的發展，從(cong) 而使這些藥物漸漸不再有效。ARB菌株更加耐受溫和的熱處理方法，如食品加工中的巴氏殺菌法，這將嚴(yan) 重威脅到食品安全。此外，由於(yu) 微生物組多樣性對宿主健康有顯著影響，而競爭(zheng) 排斥原理認為(wei) 腸道微生物多樣性越高，病原菌定植的可能性就越低。在孵化場和養(yang) 蝦場使用抗生素會(hui) 破壞腸道微生物的動態平衡，因此這也可能導致情況惡化。

The conventional approaches for preventing and curing AHPND either have limited success, or are unsustainable in the long-term. Mixed in the shrimp diet or added to rearing water, antibiotics are used as powerful medicines to fight bacterial infections in shrimp production. However, their use presents a serious threat to public health and the environment. Additionally, there is growing antibiotic resistance which is curbing the effectiveness of these drugs. Continuous application of antibiotics by shrimp farms facilitates the development of antibiotic-resistant bacterial (ARB) strains. Antibiotic-resistant strains can be more tolerant to mild heat treatments, such as pasteurization in shrimp processing, which will threaten food safety. Further, it has been proved that microbiome diversity significantly impacts host health. The competitive exclusion principle, which is also known as Gause's law of competitive exclusion, states that the higher gut microbial diversity, the lower the possibility for pathogenic colonization. The application of antibiotics at hatcheries and shrimp farms would disrupt the microbiota homeostasis.

減輕養(yang) 蝦場弧菌感染的另一種方法是改善水質。由於(yu) 弧菌感染是概率性事件，而對蝦對致病菌的敏感性往往受到有利於(yu) 疾病爆發的水質條件的影響，因此對對蝦養(yang) 殖場的水質進行監管以防止大規模感染是很重要的。

An alternative strategy to mitigate the effects associated with Vibrio infections in shrimp farms, is to improve water quality. As Vibrio species are opportunistic, the susceptibility of Vibrio infection to shrimp is often affected by water conditions that favor a disease outbreak, which raises the urgency to manage the water quality of shrimp farming to prevent mass infection.

此外，維持池塘和對蝦胃腸道中藻類和細菌之間的生物平衡也是減少AHPND感染影響的有效途徑之一，使用益生菌可以抑製對蝦的某些細菌感染。然而，實際上益生菌或其天然產(chan) 物是否真的抑製了水產(chan) 養(yang) 殖池塘中的某些諸如弧菌的病原菌目前尚不清楚，具體(ti) 的抑製途徑與(yu) 機理也有待進一步探究。而關(guan) 於(yu) 不同益生菌在水產(chan) 養(yang) 殖中對對蝦的協同保護作用也尚不清楚。

Besides, maintaining the biological balance among algae and bacteria in ponds and the gastrointestinal tract of shrimps is also one of the ways to reduce the effects of AHPND infection. The use of probiotics to inhibit certain bacterial infections in shrimps and enhance water quality has proved to be valid for aquaculture purposes. However, it is unclear whether the actual probiotics or their natural products actually inhibit certain pathogenic bacteria like Vibrio in aquaculture ponds. There is limited knowledge on the synergistic protective effects of different probiotics on shrimp in aquaculture.

最近的研究發現，對蝦免疫係統會(hui) 對AHPND作出響應，分泌抗菌肽（AMP）（如penaeidin和crustin）。此外還發現多種免疫相關(guan) 因子在對蝦體(ti) 內(nei) 具有抗菌作用，注射這些因子的重組蛋白可以有效預防AHPND。同時，一些植物提取物以及噬菌體(ti) 也可作為(wei) 潛在的抗菌劑來抑製副溶血性弧菌的生長。它們(men) 已經被應用到對蝦飼料中，以最大程度地減少病原體(ti) 的影響，提高對蝦的存活率。

Recent research has found that, in response to AHPND, the shrimp immune system expresses antimicrobial peptides (AMPs) such as penaeidins and crustins, which provide some protection against AHPND-causing V. parahaemolyticus. Several immune-related factors have been discovered to be antibacterial in shrimp, and the injection of recombinant proteins of these factors can be an effective treatment to prevent AHPND. While some plant extracts and phages (bacterial virus) can serve as a potential antimicrobial agent to inhibit the growth of V. parahaemolyticus, they have also been successfully utilized as feed supplements in the shrimp diet to minimize the effect of pathogen and improves the survival of shrimp species.

盡管與(yu) AHPND相關(guan) 的研究取得了許多進展，但PirA/B引起AHPND的潛在機製仍不清楚。pVA1毒力質粒的關(guan) 鍵信息，包括每個(ge) 細菌細胞內(nei) 的質粒拷貝數的變化及其對AHPND發病機製的影響仍是未解之謎。因此，AHPND的發病機製還需要進一步的研究。

Despite the progress in AHPND-related research, the potential mechanisms of PirA/B that cause AHPND in shrimp remain unknown. Although many reports related to the pVA1 virulent plasmid, the critical information remains a mystery, including variability of the plasmid copy number per bacterial cell and how this influences the pathogenesis of AHPND, indicating further investigatory for the pathogenesis of AHPND is also needed.

目前AHPND的診斷主要通過觀察患病對蝦的臨(lin) 床症狀，此外也有對病原菌利用包括PCR擴增檢測、分子診斷工具等方法進行檢測。但目前尚無可用於(yu) 現場檢測且有效快速的檢測方法。綜上所述，我們(men) 仍然迫切需要針對該病的有效的診斷、治療、預防和管理手段，以應對未來可能出現的大規模疾病暴發。

The current diagnosis of AHPND includes the examination of the affected shrimps through the clinical symptoms of AHPND, PCR amplification detection, molecular diagnostic tools, etc. However, effective methods, used on-site and in-time, have not been established to help diagnose AHPND. In summary, effective prevention, treatment, diagnosis, and management of this disease are still in urgent need to take precautions and deal with further outbreaks.