A US$1,000 prize on the road to 300,000 tonnes

16 November 2026

Part 8 of 18 · A history of the giant freshwater prawn

On 9 October 2013, in Paris, a professor from Israel’s Ben-Gurion University was handed a plaque — and a full US$1,000 cash prize. His trip to the conference was paid on top of that. For solving one of the biggest problems every prawn hatchery knew: someone had to sort the juveniles by sex, by hand.[1][2]

Why sort them at all? Because in a mixed pond, the males slow the females down. In a cage study published in 1986, prawns stocked as all males produced 473 grams per square metre in 150 days; all females, 248 grams; a mix of the two, 260. Females raised with males grew worse, while the males hardly noticed the females.[3] Before Sagi’s method, the way to stock a pond of males was to pick them out of the hatchery batches one young prawn at a time, looking for the appendix masculina, a tiny appendage only males carry.[4]

Sorting by sex was only the newest in a line of workarounds the industry had built around the prawn’s uneven growth. Farmers sorted young prawns by size before stocking them. Through the season they harvested the biggest males again and again, and the smaller ones, freed from their bosses, grew on: the promotions of the office pond, used as a harvest plan.[5]

On practices like these, production grew from about 17,000 tonnes in 1993 to about 195,000 tonnes in 2002.[6] It grew despite the one problem the industry could not work around: disease. In the mid-1990s, a hatchery in Guadeloupe, in the French West Indies, reported a new one, white tail disease, caused by a virus and a smaller satellite virus that depends on it.[7] It has since been reported from Martinique, Taiwan, China, India, Thailand, Malaysia and Australia.[7] In a hatchery tank, it often kills every larva within two or three days of the first signs, and in India it probably arrived with prawn seed imported from Taiwan and China.[8]

The 2013 prize took the newest of the workarounds, sorting by sex, and built it into the hatchery. Amir Sagi’s group had spent twenty years studying the gland that makes a male a male. What came out was a way to breed batches of young prawns that were all male, using a temporary treatment that switches a gene off for a while, with no hormones, no chemicals and no genetic modification.[1][2]

It did not end the aquatic office politics. In an all-male pond, the males still sort themselves into bosses and juniors, and farmers still grade and harvest.[9] In one American trial, all-male ponds ended the season with more orange-claw males than mixed ones.[10] What changes is the maths. In Indian ponds, all-male stocking produced 30 per cent more prawns than a mixed pond, and 62 per cent of them reached a size worth selling, against 47 per cent.[4] In Israeli ponds, all-male prawns reached market size sooner, so the partial harvests could start earlier.[11] By 2021, the industry was producing about 300,000 tonnes a year.[12]

The industry arrived there without answering the question this series keeps returning to: how one prawn slows another’s growth, whether by contact, as the bosses do, or through something in the water, as the experiments of the 1980s suggested. Grading, harvesting and single-sex seed all act on the pond, not on the prawn. As far as I can tell, that is the quiet achievement of the industry, and also the reason the question is still open.

Picking this topic up again in 2026 means going back to the papers of the 1980s, and reading them by the standards of today.

Sources

1. World Fishing & Aquaculture (2013), Aquaculture award. Amir Sagi, Ben-Gurion University: the inaugural Novus Global Aquaculture Innovation Award for all-male Macrobrachium rosenbergii through temporal RNA interference; no chemicals, hormones or genetic modification; presented at GOAL 2013, Paris, 9 October; 16 entries from 11 countries; chosen because it addressed manual sorting of juveniles by gender. worldfishing.net
2. Global Aquaculture Alliance (2013), Ben Gurion University professor wins inaugural aquaculture innovation award. Twenty years of androgenic-gland research; a plaque, a US$1,000 cash prize and an expense-paid trip to GOAL 2013. globalseafood.org
3. Sagi, A., Ra’anan, Z., Cohen, D., Wax, Y. (1986), Production of Macrobrachium rosenbergii in monosex populations: yield characteristics under intensive monoculture conditions in cages. Aquaculture 51: 265–275. 473, 248 and 260 g/m² in 150 days; females inhibited by males, males hardly influenced by females. cris.huji.ac.il
4. Production potential of early segregated all-male population of Macrobrachium rosenbergii (de Man) in tropical earthen pond condition (2009). Indian Journal of Fisheries 56(3): 195–198. Sexes segregated by hand by the appendix masculina; all-male production 30% higher; 62.3% against 47.1% marketable. epubs.icar.org.in
5. New, M. B. (2002), Farming freshwater prawns, FAO Fisheries Technical Paper 428, Annex 8, Size management. Grading; selective harvesting of the largest prawns. fao.org
6. FAO (2009), Cultured aquatic species fact sheet: Macrobrachium rosenbergii. Global production, 1993 and 2002. fao.org
7. White tail disease of freshwater prawn, Macrobrachium rosenbergii, Indian Journal of Virology 23(2): 134–140 (2012). First reported from Guadeloupe, then Martinique, Taiwan, China, India, Thailand, Australia and Malaysia; MrNV and XSV. pmc.ncbi.nlm.nih.gov
8. Sahul Hameed and colleagues (2007), on white tail disease in India (PubMed 17928085): mortalities often reaching 100% within two or three days; probable origin in seed imported from Taiwan and China. pubmed · OIE (WOAH) aquatic animal disease card, white tail disease (2007). woah.org
9. Nguyen, D. M., et al. (2026), feminisation of all-male postlarvae of the giant freshwater prawn. Fishes 11: 252. The male hierarchy and the transition of orange-claw males still produce size variation at harvest. mdpi.com
10. Production characteristics of all-male and mixed-sex giant river prawns, Macrobrachium rosenbergii, grown in earthen ponds in Kentucky and Mississippi, USA (2015). More orange-claw males in all-male ponds; heavier final weights. agris.fao.org
11. Cohen, D., Sagi, A., Ra’anan, Z., Zohar, G. (1988), The production of Macrobrachium rosenbergii in monosex populations. II. Israeli Journal of Aquaculture – Bamidgeh 40(2): 57–63. Market size reached earlier; partial harvests from three months. cris.bgu.ac.il
12. Pillai, B. R., Panda, S. (2024), estimates of global production for 2021, about 300,000 t. journalofaquaculture.com

Part 8 of 18 · A history of the giant freshwater prawn · Previous: Part 7, Scampi for Europe · Next: Part 9, Diving into the research archives · SHRMP.bio’s strategy behind it: shrmp.bio/strategy.html