When the temperature drops sharply continuously and especially when it rains, it is necessary to prevent the diseases of shrimps caused by stress. Those diseases include red leg, red tail, red feelers, broken feelers, red gut and stomach, red shrinking hepatopancreas and EMS, etc.
Why the dropping temperature or rain causes stress to shrimps? The following are the possible reasons.
1. Large amount of fresh water pours into the pond when it rains, which causes the salinity drops sharply
2. Large amount of fresh water pours into the pond when it rains, which causes the pH drops sharply
3. Large amount of fresh water pours into the pond when it rains, which causes the temperature drops sharply
4. Large amount of fresh water pours into the pond when it rains, which causes the separation of fresh water and sea water, and the dissolved oxygen at the bottom of the pond is reduced
5. Due to sharp changes in salinity, pH, and temperature, the balance between algae and bacteria is broken. Algae in the water body may die, beneficial bacteria may die, pathogenic bacteria may multiply and a large number of terrestrial bacteria may be brought into the pond.
6. The strong wind may cause big waves in the pond and as a result, the hydrogen sulfide, ammonia nitrogen, residual bait, animal and plant corpses, excreted feces and other harmful substances at the bottom of the pond are stirred, causing worsening of water quality and increasing biological oxygen consumption, which makes the bottom water quality even worse.
7. Strong wind and big wave may frighten the shrimps and cause stress.
Dropping temperature and rain are the main causes of shrimp diseases
The effects of dropping temperature include:
One, dropping temperature causes stress on shrimps and causes liver problem and soft shell problem. Two, dropping temperature may cause death of algae and thus influence the water quality. Therefore, it is important to prevent stress caused by low temperature and protect the algae and water quality.
Usually after rains and storms, the water quality is getting worse. The dissolve oxygen and pH will be decreased, which causes stress on shrimps and is the main cause of shrimp diseases.
1. Yellow and Black Gill
After the rain, the temperature difference in the water body causes the death of large amount of algae, producing more organic particles in the shrimp pond, which are likely to adhere to and block the gills, in addition to the effects of reduction in dissolved oxygen and pH, bacteria, polycondensation insects, etc, impairing the functionality of the shrimp gills (swollen gills), so after the rains, yellow or black gills often occurs to shrimps, causing breathing difficulties, body poisoning, poor health and eventually unsuccessful molting and death.
2. Separation of water layers & Jumping shrimp
After rains, if the water body is not stirred, the salinity of water will be reduced, the temperature will be different between layers. Because the dissolved oxygen at the bottom is insufficient, it is very likely to have jumping shrimps. Even in some areas in the water body, shrimps may die due to lack of sufficient oxygen in molting process.
3. Organic Pollution
When there is too much organic pollution at the bottom of the pond, once the temperature changes sharply, in case of water convection, the hazard articles at the bottom of pond will be spread to other areas of pond, for which, the content of ammonia nitrogen, nitrite, hydrogen sulfide and other harmful substances will rise to excessive level and cause outbreak of EMS and other diseases of shrimps.
4. Red Body Disease
Continuous rains are very likely to cause the fast reproduction and growth of vibrio and other pathogens. Once infected with those pathogens, it will be very common to see red feelers, red body and even red feet of shrimps. thus causing enteritis, liver atrophy or erosion, anorexia, and even death. Soft shell and red body are very common after unsuccessful molting process and the shrimps will die very soon.
Treatment with Stress on Shrimps in case of dropping temperature and rains
Anti-stress activities consume a large amount of energy. The immunity of shrimps will be reduced after anti-stress activities and thus shrimps are very likely to be infected by hazardous bacteria. Therefore, it is necessary for the aquaculture farmers to pay more attention to the diseases caused by stress on shrimps.
What-to-do in case of rains
First of all, during storms and rains, the water body will be separated into different layers for different temperature and salinity, which cause great stress on shrimps. Therefore, the aerator should be turned on and keep working to supply oxygen and accelerate the mixing speed of rain and pond water to avoid separated layers for different temperature and salinity, which may cause lack of oxygen in water body, death of algae and stress on shrimps.
During heavy rains, in order to prevent anaerobic reactions at the bottom of the pond, which will produce toxins, it is recommended to use granular oxygen, calcium peroxide powder and other slow-release aeration products. In severe cases, a small amount (usually 100-150 grams per acre area) of sodium hydrogen persulfate tablets (used when pH higher than 8.0) or potassium ferrate tablets (used when pH lower than 8.0) can be used to oxidize the oxygen consumption factors at the bottom of the pond to reduce oxygen consumption in the water body . All the operations mentioned above can be carried out before the rain.
Next one is about the drug use. During rains, the shrimps have to adapt to the salinity changes by adjusting the internal osmotic pressure. In this process, a large amount of energy will be consumed. Once the energy supply is insufficient, the shrimps will suffer serious stress and even cause hepatopanceas diseases. Therefore, during this period, the feed should be controlled rather than stopped (generally, the feeding rate can be reduced by 3-5% according to the impact of rain on the shrimps). At the same time, some anti-stress products, e.g. bile acids should be added to effectively improve the physical fitness, protect hepatopancreas health, improve the anti-stress ability of shrimps) and polysaccharides and marine red yeast etc. to provide energy. When the physique of shrimps is poor, or the water quality of pond is bad, the above-mentioned drugs can be sprayed to protect the health of shrimps and prevent shrimps from diseases.
What-to-do after rains
What-to-do after rainstorms is the key to decide whether the whole pond of shrimps can survive the rainstorm period safely and whether the shrimp can return to normal status quickly after the rain, and resume feeding and growth.
First of all, the rains will cause the change of salinity, which may stimulate continuous long-term molting, causing soft shell, double shell, edema and other diseases. And once there is a heavy rain during this period, it is required to the use of trace elements, calcium supplement products and fully water-soluble multivitamins (mainly water-soluble vitamin D) to treat those problems except for some more serious conditions. Those medicines are usually used at night. If the physique is obviously getting worse due to continuous molting, or shrimps lost vitality and become unable to jump, bile acids are recommended to use.
The pH of the water body must be checked immediately after the rain stops. A sudden drop in pH after rain will reduce the absorption rate of dissolved oxygen in the blood of the shrimp and cause functional hypoxia for which, aeration will not help. When the pH≤8.0, it can be adjusted with slaked lime (mainly calcium hydroxide) or weathered lime (mainly calcium carbonate) 30-60 kg per acre. If the water bubble is significantly reduced while the pH is low, and the water quality becomes sticky and slippery, it is possibly that the soluble organic matter in the water or at the bottom of the pond is increased and it is required to splash 600 grams of potassium powder or chlorine dioxide powder per acre, to oxidize the organic matter in the water body, once every 8-12 hours if the situation is serious. After continuous oxidation, the bacteria will be decomposed the next day to reduce the oxygen consumption of the organic matter in the water body. Liver diseases, usually red liver, or even worse, white liver and liver atrophy, it is recommended to use bile acids immediately, 3g mixed with 1 kg of feed. And it only takes 7 days to restore the health of the shrimp liver.
對蝦應激出現紅腿紅尾、肝腸發紅、萎縮，偷死，如何防治？
持續降溫外加雨水助攻，養殖戶要謹防對蝦應激紅腿紅尾、紅須斷須、腸胃發紅、肝胰臟發紅萎縮，偷死等情況。要如何處理？
1、因為降雨，大量淡水注入池塘，引起池水鹽度急劇下降
2、因為降雨，大量淡水注入池塘，引起池水pH急劇下降。
3、因為淡水大量注入池塘，引起水溫下降較大。
4、因為淡水大量注入池塘，引起海淡水分層現象，使池塘底部水層溶氧下降。
5、因鹽度、pH、溫度急劇變化，引起池塘水體原來平衡的藻相、菌相失衡。原來水體的藻類可能死亡，有益細菌可能死亡，病原菌可能大量繁殖，大量陸地細菌可能被帶入池塘
6、因大風引起池塘湧浪，大浪淘底，使原來沉積在池底的硫化氫、氨氮、殘餌、動植物屍體、排洩糞便等有害物質被淘起，引起水質敗壞，生物耗氧量上升，特別是使池塘底層水質更差。
7、因大風、湧浪使對蝦受到驚嚇，引起對蝦應激反應。
降溫主要的影響在於兩個方面：一是使水溫下降，此時對蝦容易應激反應，肝臟病變、出現軟殼等症狀，二是溫度下降導致藻類突然死亡，腐化，影響水質。因此要做好防凍抗應激以及保藻穩水質兩方面工作。
雨後對蝦出現各種異常現象是由於陰雨天、雷陣雨或暴雨後，蝦池水質發生較大變化，特別是水中溶解氧含量和pH降低，是導致蝦產生應激反應、誘發蝦病的主要因素。
1、 黃黑鰓病
雨後由於水體出現溫差造成泛底加上藻類大量死亡導致蝦池水中有機顆粒較多，容易粘附堵塞在的鰓部，加上溶解氧、ph的下降造成蝦鰓功能性損傷（腫鰓），此外還有細菌、聚縮蟲等附著，所以雨後對蝦經常出現黃鰓或黑鰓，引起對蝦呼吸困難、體內中毒、體質差而出現蛻殼不遂陸續死亡。
2、水分層與暗浮頭、蝦跳
降雨後若無強力攪動水體，容易造成水體鹽度、溫度及溶解氧分 層。往往出現底層氧氣不足，會出現對蝦暗浮頭，常見對蝦潛遊在池水的中上層一有驚動就出現蝦跳現象，甚至出現無氧死角導致蛻殼缺氧死亡。
3、泛池與耗底
若池底的有機汙染物過多，水溫突變時，會引起水體發生對流，導致 池底的腐殖質翻動，進而帶動池底的有害物質充斥水體中，造成池水中的氨氮和亞硝酸鹽、硫化氫等有害物質含量升高超標，發生急慢性中毒導致對蝦發病、偷死等現象。
4、紅體病
連續陰雨天，容易引起養殖水體的弧菌或其他病原菌大量繁殖。導致對蝦感染細菌、蝦病發生。雨後對蝦常出現紅須，體色微紅，嚴重時遊泳足也變紅，出現應激性腸炎、肝臟萎縮或糜爛、厭食，甚至發生死亡現象。蛻殼不遂而出現病蝦甲殼軟或硬殼、體色棕紅或鮮紅，緩慢遊塘，撈出水後即很快死亡。
「應激」消耗了大量的體能，體能下降了，免疫能力就會下降，原來潛伏在體內的隱性病害就會抬頭，有害的細菌趁虛而入，容易引起對蝦發生病害，所以應激反應是水產養殖的最常見問題，必須引起養殖從業者的高度重視。
雨時處理：
首先，暴雨時水體會出現水溫分層和鹽度分層，這些都會導致對蝦強烈的不適甚至病變。所以不管降雨大小都須馬上氧機全開，不僅是為了增氧，同時還能加快表層雨水與池水的混合速度，避免雨水形成鹽度層與溫度層，從而導致水體缺氧、藻類死亡、以及對蝦滲透應激。
暴雨期間，為預防池底發生厭氧反應，產生毒素，可潑灑顆粒氧、過氧化鈣粉等緩釋型增氧產品。嚴重的還可搭配少量（一般一畝100-150克）過硫酸氫鈉片（pH超過8.0使用）或高鐵酸鉀片（pH低於8.0使用），氧化池底耗氧因子，減少水體耗氧。當然，正如前面所說，這個操作很多時候可以在雨前就提前進行。
接下來就是用藥問題了。降雨期間對蝦要適應鹽度變化（調節體內滲透壓），必需大量能量供給肌體消耗，如果體能不足就會出現嚴重的應激反應甚至肝臟病變乃至萎縮。所以，在這期間可以控料卻不能停料（一般根據降雨對蝦的影響可減料3-5成），同時還必須添加一些抗應激產品，如膽汁酸（膽汁酸可有效提高對蝦體質，保肝護肝，提高抗應激能力）、和提供能量的（如多糖、海洋紅酵母等）。對蝦體質偏弱，池塘水質、底質不好的可全塘潑灑上述藥物保蝦防病。
雨後防控：
暴雨期間的主要工作還是雨後進行的，雨後的很多處理決定了整塘蝦能否完全安全的度過暴雨時期，決定了對蝦能否在雨後用最快時間恢復正常，恢復吃料及生長。
首先要注意的是降雨造成水體鹽度變化，嚴重的會刺激連續長時間蛻殼、引發軟殼、雙層殼、水腫等病症。而一旦這段時間出現大暴雨，你就要注意用微量元素+補鈣產品+全水溶性多維（主要是水溶性維D）化水外潑，注意除較為嚴重或對蝦狀況很差的，一般這些藥在晚上使用，若是連續蛻殼導致體質明顯變差的，趴罾無力跳彈的，可以加上膽汁酸拌料。
雨停之後必須馬上檢測水體pH，因為若出現降雨引發的pH急降，會導致對蝦血液的溶氧吸收率降低，引發功能性缺氧，這時再多的增氧也無濟於事。當pH≤8.0，可用熟石灰（主要是氫氧化鈣）或風化石灰（主要是碳酸鈣）一畝5-10斤來調節。若是pH偏低的同時出現水體泡沫明顯減少，水質變得粘稠滑膩的，這是水體或池底可溶性有機物增加的外在表現，就得趕緊潑灑過鉀粉或二氧化氯粉一畝100克，氧化水體有機質，嚴重的8-12小時一次，連續氧化之後次日補菌分解，減輕水體有機物的耗氧。肝臟疾病，常見是紅肝，嚴重的出現白肝和肝萎縮，可立即使用膽汁酸，3g拌一公斤料，7天可快速恢復對蝦肝臟健康。
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