The larvae that needed the sea

05 November 2026

Part 1 of 17 · A history of the giant freshwater prawn

A newly hatched giant freshwater prawn is just under two millimetres long, and it swims tail first, upside down.[1] What a giant to be.

It hatches where the river meets the sea. A female carries her eggs, between 5,000 and 100,000 of them, in a brood chamber under her tail for about three weeks, and travels downstream to the estuary to release them.[1] There, in brackish water, the larvae pass through eleven stages, growing to almost eight millimetres, before they change into postlarvae: small prawns that swim forwards and the right way up, having worked out, at last, which way is up. Then they head back upriver. Where the water recedes, they walk, over wet stones, up small waterfalls and weirs, even across land.[1] Quite an adventure, and not one you might expect.

For anyone trying to farm the species, that journey was the problem. People could catch young prawns in rivers and raise them in ponds. And they did, long before anyone could breed them.[2] But the larvae need the brackish water of the estuary. In fresh water, they die.[3]

The man who worked it out was Shao-Wen Ling, an expert working for the UN’s Food and Agriculture Organization at the Fisheries Research Institute in Penang, Malaysia, where the prawn was already prized as udang galah.[3] He took up laboratory experiments that Ariya Sidthimunka had begun in Bangkok in the 1950s.[5] In 1961 he found that the larvae of this freshwater prawn need brackish water, a mix of fresh and sea water, to survive. In 1962, rearing them in it, he succeeded. By 1963 he had enough young prawns to stock culture ponds.[4] Modern farming of the species starts there.[1]

It mattered far beyond Penang. In 1962, the marine shrimp the world already traded could not yet be bred in hatcheries at any commercial scale, so a large prawn that could be raised in a tank looked like the obvious route to farming crustaceans.[2][6]

Hatcheries still follow Ling’s water. Larvae are usually reared at about twelve parts per thousand of salt, roughly a third as salty as the sea, and most turn into postlarvae after about a month.[1]

In 1965 and 1966, Takuji Fujimura’s team took thirty-six prawns from Malaysia to a research centre in Honolulu.[7][8] Aloha.

Sources

1. FAO (2009), Cultured aquatic species fact sheet: Macrobrachium rosenbergii (text by M. B. New). Larval size and stages, swimming and walking, eggs, hatchery salinity and timing. fao.org
2. New, M. B. (1987), Freshwater prawns: status of global aquaculture. FAO. Wild young grown on in ponds; the state of marine shrimp breeding; Hawaii 1965–66. fao.org
3. Ling, S. W., The general biology and development of Macrobrachium rosenbergii (De Man). FAO. Udang galah; larval stages require brackish water. fao.org
4. FAO Bay of Bengal Programme, freshwater prawn hatchery manual (BOBP/MAG/13). 1961 discovery, 1962 success, 1963 pond stocking. openknowledge.fao.org
5. Singholka, S., New, M. B., Vorasayan, P., The status of Macrobrachium farming in Thailand. FAO. Sidthimunka’s 1950s experiments, taken up by Ling. fao.org
6. Fujinaga (Hudinaga), M., Kuruma shrimp (Penaeus japonicus) cultivation in Japan. FAO. First laboratory rearing 1933; large-scale commercial rearing by 1967. fao.org
7. Genetics and Molecular Biology (SciELO), on the introduction of the giant river prawn: Fujimura’s team took prawns from Malaysia to Honolulu in 1965. scielo.br
8. University of Southern Mississippi, microsatellite study of cultured giant freshwater prawn: 36 prawns introduced to Hawaii from Malaysia, 1965 and 1966. aquila.usm.edu

Part 1 of 17 · A history of the giant freshwater prawn · Previous: Prologue, The giant prawn Australia hasn’t farmed (yet) · Next: Part 2, The hatchery that gave its prawns away · SHRMP.bio’s strategy behind it: shrmp.bio/strategy.html