A milestone in aquaculture research has been achieved at the Seawater Laboratory of the Division of Marine Studies at the University of the South Pacific.
Larvae of the Monkey River Prawn Macrobrachium lar have been for the first time ever in captivity successfully reared through the planktonic larval phase of their lifecycle to metamorphosis into the post-larval stage, a development that has taken humanity a step closer to realising the species' potential for farming.
This species, also known locally as uradina, is indigenous to Fiji and a number of other Pacific Island countries including the Solomon Islands and Vanuatu; and is the basis of significant inland fisheries, the catches of which currently dominate the sales at local markets.
Macrobrachium lar has been a focus of research to assess its potential for aquaculture for a number of decades, with the hope that it will be farmed much like its cousin the Malaysian Giant Freshwater Prawn Macrobrachium rosenbergii whose annual production value in Asia alone is estimated at around one billion US dollars.
The Monkey River Prawn has a number of favourable characteristics for aquaculture, which include its large size, wide acceptance amongst local communities as a delicacy, and the fact that it is able to survive out of water for short periods of time.
Another important characteristic of the species is that it is indigenous to many of the Pacific Island countries where there is interest in developing freshwater prawn farms. If research on M. lar culture techniques allows for the easy breeding and rearing of the species, then the introduction of an exotic prawn species would no longer be necessary to establish freshwater prawn aquaculture in the Pacific islands.
A major drawback to further research into the suitability of M. lar for culture - until now - has been the inability to grow young prawns known as Post-larvae or PL in the laboratory after hatching from the egg. This meant that PL for any research work had to be sourced from the wild, which proved to be time consuming and tedious. This was also a barrier for future farming operations involving the species as the easiest way to produce the large numbers of PL required for farming is in a hatchery.
The earliest published attempts at growing the larvae of M. lar in the laboratory all the way through to the post-larval stage was by a researcher named Wilbert Kubota in 1972 at the University of Hawaii, followed by John Atkinson in 1977 at the same institution. More recently at USP, Mr. Satya Nandlal has recently completed his PhD thesis in Marine Science on the aquaculture of M. lar, including extensive field trials and attempts to rear the species to the PL stage. Unfortunately, all studies were able to grow larvae up to a certain point until all larvae died prematurely.
The success of this study in reaching PL can be attributed for the most part to the development of a suitable feed which meets the nutritional requirements of the larvae in addition to culture at its preferred salinity level in an appropriate rearing environment.
Another finding of this study is that the larvae of M. lar develop through approximately 13 stages in the ocean until they change into post-larvae. After they become post-larvae, the animals migrate landward and eventually settle in high-elevation freshwater streams far inland. A total of five post-larvae were able to be produced in the current study, metamorphosing after 77, 78, 85, 101 and 110 days of culture respectively.
The current research at USP is funded by ACIAR (the Australian Centre for International Agricultural Research) in collaboration with the Secretariat of the Pacific Community (SPC).
The study was undertaken by Master of Science student Monal Lal and supervised by Mr. Johnson Seeto of USP and Dr. Timothy Pickering of SPC. A new technique for rearing prawn larvae developed by JICA (Japan International Cooperation Agency) Senior Volunteer Mr. Tomohiro Imamura while at USP was instrumental in achieving this outcome.
There is scope for much more research into this species, and the work done has demonstrated that the larval rearing of M. lar in the hatchery is technically feasible, which is an important step towards further developing and refining techniques for its culture.