“We shifted out of paddy in the 1990s as the area, being low lying, was prone to flooding during monsoon. Initially we opted for fishing but then moved to shrimp in a big way after the Vannamei variety became popular," explained Raju.

Nellore, another Andhra Pradesh town down south, was the shrimp capital of India until recently. At the time, Black Tiger prawns, a large species of marine shrimp, were in demand. Around 2006, the world began shifting to Vannamei or pacific white prawns, for reasons more economic than the taste.

Vannamei requires less or almost zero salinity to farm. This means that they can be raised farther from the sea-Bhimavaram is located about 25 kilometres inland. This species also allows higher stocking. A farmer can raise as many as 100,000 shrimp on an acre-sized pond as against 25,000 in the case of Black Tiger prawns.

Also, Vannamei requires just 90-120 days of cultivation. Black Tiger prawns, on the other hand, have to be grown for up to 180 days.

In short, Vannamei was more attractive for the entire ecosystem. Lower farming time meant farmers could do three crop cycles a year, exporters could scale up their operations and retail chains had an assured supply. Today, Vannamei accounts for 90% of the shrimps raised across the world. The Black Tiger prawn's share has declined to just 9%.

A typical cycle, Raju explained, starts with sourcing of shrimp seeds from hatcheries that import the broodstock (parent shrimps) from the US.

The seeds are then grown in large ponds, each measuring five acres or more for 90 to 120 days. The challenge here is to maintain the water quality and provide the right quantum of feed.“The first 60 days are critical as the shrimp grows to weigh 100 grams," explained Pavan Nadimpalli, a cultivator with a 3-acre farm. He also operates one of the many aqua labs that dot the town. They are needed to test the water quality and health of the shrimps periodically.

At 60 days, even if disease strikes, the farmer can harvest and recover part of the cost from the unaffected stock.

A farmer gets around ₹220 per kg for '100-count', which is about 100 shrimps, and that is a break-even price at current costs, he added. The price increases as the count drops. A '30-count' (30 shrimps make up 1 kg) fetches a price of ₹400 per kg. For that, the shrimps have to grow for more than 90 days. Once the shrimp is harvested, it is frozen and taken for processing before export.

“We make money only if we are able to cultivate shrimp for a longer duration. That is possible only if there are no diseases. If disease strikes before 60 days, the crop is totally lost," said Krishnam Raju, another Bhimavaram farmer. In recent cycles, he and his fellow farmers have struggled to farm shrimp beyond 60 days.

The latest incidence of disease is alarming, admitted Balasubramaniam of the Prawn Farmers Federation of India. What is more alarming is that the pathogen that is causing the disease and spreading like wildfire is yet to be identified.“The disease typically strikes 45 days after the seed is purchased. Within a week 10% of the crop is lost. In four weeks, if not harvested, 50% is gone," he added.

Diseases have killed the aquaculture sector in South East Asian countries such as Thailand and Taiwan in the past. If not tackled on a war footing, Indian shrimp output could fall sharply, he warned.

The increase in cases of disease has cast doubts on India's approach to genetic selection. The government follows a pathogen exclusion approach. It allows import of pathogen-free broodstock (parent animals), which are then mated in India by hatcheries to produce eggs. This approach, scientists say, has worked well so far, causing shrimp production and exports to grow rapidly. But the rise in pathogens from water and soil is testing this model. Calls have been made to adopt the pathogen exposure approach that countries such as Ecuador follow.“In Ecuador, they constantly expose the shrimps to various pathogens and build their immunity. Their success rate, as a result, is as high as 85%," said Balasubramaniam.

The long-term solution, both farmers and exporters agree, is developing an indigenous broodstock that can handle local conditions and pathogens better.“Vannamei has been around for more than a decade. The scientific community should have looked into this much earlier," rued Kumar from the Seafood Exporters Association.

Though India exports shrimp to over 90 countries, the bulk of the volumes goes to the US, China and the EU. Exporters love the US market as it takes up huge volumes at premium prices. Other markets are not that attractive. China, the second-biggest market, is very price conscious and prefers smaller sizes. The EU, where each of the 27 nations has different tastes and rules, is a compliance nightmare.

But India's reliance on the US market faces another challenge apart from Trump's high tariffs. A couple of senators have proposed 'The Indian Shrimp Act', which if passed, will impose an anti-dumping duty of up to 40% over and above the existing tariff. Their grouse: India is dumping shrimp in the US at cheap prices. The US currently has an anti-dumping duty of 2.49% and a countervailing duty of 5.27% on shrimp, taking the effective tariff to 58%. Experts opine that such efforts have been made in the past but have failed. Nevertheless, there is fear within the industry because of the prevailing political environment in the US.