Pinoys have kept Ulang or Giant River Prawns for decades. Here’s why they’re more sustainable alternatives to Hipon and Sugpo, with the potential to take a larger share in the global market.

When people think of shrimp, what usually comes to mind? We’d bet a bag of Oishi most would picture Whiteleg Shrimp (Litopenaeus vannamei) or Tiger Prawns (Penaeus monodon), both of which spurred multi-billion dollar industries, making both aquaculturists and seafood lovers pretty happy.

But there’s a new shrimp on the block – and it might soon claw its way from the rivers of Asia to groceries and restaurants worldwide.

The Giant River Prawn (Macrobrachium rosenbergii) or Ulang is well-known to most aquaculturists. The eureka-ish discovery that its larvae needed brine to survive beyond five days is the stuff of aquaculture legend. But most cosmopolitan seafood consumers don’t know much about it.

It’s the largest member of Macrobrachium, a genus meaning ‘big arms’ in the order Decapoda – which include crabs, shrimp, prawns, lobsters, crayfish and other familiar critters seafood consumers crave.

The 240 or so Macrobrachium species have a tropical and subtropical distribution, inhabiting numerous rivers, ponds, lakes and streams across every continent except Europe and Antarctica.

Most species are amphidromous and require both fresh and seawater to complete their lifecycles. Eggs wash downstream to the sea, then metamorphose into juveniles which crawl as far as 100 kilometers upstream to breed and repeat the cycle.

Ulang grow much larger than any other Macrobrachium species. Females reach 25 centimeters while the larger males top out at 32 centimeters, excluding their impressive claws or chelipeds which can breach 60 centimeters.

Males are divided into three morphotypes – small males (SM) have short translucent claws, mid-sized orange claws (OC) have large yellow-orange claws as long as their bodies, while large blue claws (BC) have bright blue claws twice as long as their bodies. Blue claws dominate orange claws, while small males sit at the bottom of the heap. The presence of higher-caste males inhibits the growth and development of both males and females.

Wild Ulang live in shallow, muddy lakes and rivers with good vegetation. Able to crawl on land and even up relatively vertical surfaces like waterfalls, they are largely nocturnal – lazily spending days half-buried in mud and detritus. As night falls, they forage and hunt for worms, crustaceans, mollusks, fish and carrion. People have caught and eaten Ulang for thousands of years in Asia but modern farming began just a half-century ago.

Ulang In Aquaculture

Generations of river and lakeside communities in Southeast Asia, particularly in the Philippines, Myanmar and Bangladesh, have long stocked Ulang in pens and pools, but science-based farming began only in the 1960s. The first major Ulang aquaculture breakthrough was in 1961, when Food and Agriculture Organization (FAO) expert Shao-Wen Ling discovered that Ulang larvae required brackish water to survive beyond five days.

This finally allowed aquaculturists to produce enough juveniles for grow-out experiments in ponds by 1963. Hawaii-based fisheries biologist Takuji Fujimura followed-up this discovery with a system for commercial mass-rearing by 1972, spurring the first Ulang business ventures in Hawaii and other countries.

Research and development projects eventually sprouted in Asia, Europe, the Americas and Africa, with the United Nations Development Programme (UNDP) funding Ulang farm research in Thailand in the 1980s, helping the country produce 3000 tonnes by 1984.

By 2012, annual global Ulang production had ballooned to 220,254 tonnes, valued at USD 1.2 billion. According to FAO’s 2014 data, the top producers in 2012 were China (57%), Bangladesh (19%), Thailand (11%), Vietnam (4%), India (3%), Taiwan (3%) and Myanmar (2%), with Asia supplying over 98% of global trade.

Culture Protocol

Farming Ulang requires a bit of consideration. Commercial hatcheries take from 32 to 35 days to produce post larvae (PL) using 12% brackish water plus a mixture of live brine shrimp and egg custard for food. Hatcheries are either flow-through or use a Recirculating Aquaculture System (RAS). Pond stocking densities can range from one to four prawns per square meter in extensive systems to up to 20 prawns per meter in intensive systems. A big challenge is that males are aggressive and not only fight, but cannibalize each other, leading scientists to develop novel solutions, discussed later.

Though they can subsist on natural pond biota, five to seven months of supplemental pellet feeding are standard before harvesting. With dry pellets containing from 30% to 35% protein, an FCR of 3:1 or even 2:1 can be achieved. Polyculture systems with freshwater fish can further lower this as the prawns can subsist on detritus, leftovers and faeces.

Sorting should be done from the 5th to the 11th month to catch and sell the larger blue clawed (BC) males. When removed, the less-dominant orange clawed (OC) males in turn evolve to become BC males. Without removing the dominant BC caste, males never fully metamorphose into the latter, larger stages and the batch suffers from cannibalism. After a year, the entire pond should be drained and the remaining harvest brought to market.

Harvesting And Processing

A key step after harvesting is proper handling as processed Ulang can become a bit ‘mushy’ when their internal organs are crushed by improper harvesting, transport and storage. Ulang cannot be piled or stacked like other shrimp as their internal organs are easily prone to damage, greatly lowering meat quality. FAO recommends icing and washing Ulang in chlorinated water immediately upon harvest, right by the pond’s edge.
Post-processing after harvest is much more important for Ulang than most other types of seafood as their meat – and market value – degrades fast if not well-tended.

Why Farm Ulang?

Farming Ulang has many advantages, being highly-profitable and applicable for both inland large-scale and artisanal or small-scale aquaculture. The prawns can sell for over USD15 per kilogram, so large-scale farming can reap good returns.

Ulang are particularly suited for freshwater polyculture with carp, tilapia, barbs, pangasius and other fish as they require very little input or cost and can make unused pond substrates productive and profitable.
Throughout Asia and Brazil, it has been found that adding Ulang to ricefields is also ecologically sound – reducing the need to produce rice with pesticides. The prawns eat pests and other insects, improve soil fertility and feed on the seeds of common rice-field weeds, while the rice absorbs the nutrients discharged by Ulang, resulting in better water quality for ricefields.

The Way Forward

One of the biggest challenges is that Ulang are familiar mostly to Asian consumers, instead of a truly cosmopolitan market. Unlike Whiteleg Shrimp and Tiger Prawns, Ulang have yet to become mainstays of the global seafood industry.
A good strategy might be to better market and package the species, similar to how pangasius was globally marketed as cream dory. Possible names can be blue shrimp, blue prawn or even river lobster as an easier and more quickly-produced alternative to marine lobsters.

“The key is to enticingly ‘dress-up’ Ulang displayed in markets and groceries so they look more delectable to consumers,” says Gilbert Pang, co-founder of Asia Aquatixs. “We were quite surprised to find that buyers were willing to pay more for both live and frozen Ulang compared to Whiteleg Shrimp or Tiger Prawns. This might be because marketable Ulang are a bit larger and because public impression of Ulang is that they aren’t farmed in sprawling commercial plots like marine shrimp.”

Eng Wah-Khoo, managing director of the Sepang Today Aquaculture Center (STAC) in Malaysia, agrees. “Demand is currently greater than supply and most of our Ulang are sold live to neighbouring Singapore at very good prices – about USD15 to USD20 per kilogram.

The freshwater prawns are already replacing Tiger Prawns in some areas. “In Thailand, Ulang are now being used as substitutes for Tiger Prawns when making Tom Yam soup,” notes Dr. Maria Rowena Eguia of SEAFDEC, an international body pushing for sustainable fisheries and aquaculture.

Increased market visibility and acceptance will dramatically boost export demand, a requirement to move this species beyond subsistence aquaculture and regional consumption to a global stage.

Monosex Ulang

The next big hurdle is that dominant male Ulang are especially vicious towards each other and cannot be reared as intensively as marine shrimp. Males fight and have a strict caste system, so only a few large blue claws will lord over a mid-sized group of mid-sized orange claws, who in turn will dominate a huge number of small, clear (and frequently unmarketable) prawns in a culture system.

Current stocking levels range from 4 to 20 per square meter or lower, compared for instance with Whiteleg Shrimp, which can be stocked to as many as 150 per square meter. The strict caste system also results in highly-variable harvests – with Ulang of varying sizes produced over the same period.

Similar to tilapia, a good solution is to create monosex Ulang to raise either all-male or all-female batches. A recent report featured by Nature Magazine highlighted a scientific breakthrough to produce monosex Ulang populations of either gender using androgenic gland cell transplantation.

A 2017 study by Levy et al found that all-female Ulang batches showed better performance than mixed-sex batches in terms of survival rate, feed conversion and yield, with harvested animals of the same size. All-female Ulang are injected with suspended hypertrophied androgenic gland cells when young.

Though female Ulang are slightly smaller than the largest BC males at 25 centimeters, most Ulang in a rearing system will reach maturity and are of uniform size. All-female monosex aquaculture is a good way of hurdling the complex and cannibalistic caste-society of Ulang males while eliminating the need for constant culling and other labour-intensive harvest and management practices.

Raising all-male Ulang batches also has distinct advantages, adds Gilbert of Asia Aquatixs. “Gene-silencing is used to induce female shrimp to produce all-male offspring. The advantage of all-male batches is that males spend much less time fighting and trying to dominate each other because there are no females to impress and mate with. Most of the animals spend their time feeding instead of fighting – shortening production time while improving productivity.”

“Size definitely matters – male Ulang grow significantly larger than females and all-male batches produce fairly uniform-sized prawns which sell for more than Whiteleg Shrimp or Tiger Prawns. More and more inland farmers are switching from marine to freshwater prawn farming because of potentially higher margins.”

With a little brains and a lot of prawn, The Fish Site is excited to see Ulang finally take their place as top contenders for the global seafood industry.