Technology and innovation are capable of increasing aquaculture production efficiency. In spite of this, the farming of giant freshwater prawns remains underdeveloped compared to the technology used for marine prawns. The causes behind this gap include the lack of suitable seeds and sites, small-scale and individualistic farming, as well as non-uniform growth. The latter in particular can be most commonly ascribed to gender, as female giant freshwater prawns grow at a slower pace than the males of the species.
Therefore, it is expected that the production of all male seeds will overcome the problem. Researchers at FRI Pulau Sayak, Kedah have moved forward in conducting this pioneering programme.
But what are the advantages that come with using all male seeds? Male giant freshwater prawns are usually culled manually after they have spent between two and three months in growout ponds. However, this method is vastly time and resource-consuming. The introduction of all male seeds will allow farmers to circumvent this stage of the process.
The acquisition of all male seeds begins with creating neo female, or “artificially male”, strains – a lengthy and complicated procedure. Such strains originate from male prawns that are sex-reversed via the elimination of androgenic glands (AG). These neo female candidates are selected from a crop of postlarvae, which have been left to mature for 45 to 60 days. At this point, many of the postlarvae’s external attributes, otherwise known as genopore complexes (GC), can be observed. The chosen few will then be brought to the lab to undergo minor surgery to remove the AG.
These glands are akin to factories “manufacturing” hormones that control sex differentiation, with the male traits of these prawns forming on the fifth walking legs. The candidates are next bred in tanks over a three-week period for a second assessment of male characteristics. This time, the fifth walking legs and second swimming legs are respectively evaluated for the presence of GC and an appendage known as appendix masculinae. The earlier surgeries are deemed a success should these two features be absent. Only then can it be determined that the giant freshwater prawns have become neo female.
Neo female prawns are subsequently kept until they reach a mature size of five to eight months. Here, the crustaceans will display elements of adult female giant freshwater prawns like short chelae (pincer-like organs) and enlarged egg sacs. Their ovaries are intermittently checked for progress.
Those with mature ovaries will be crossed with normal male strains. Results have shown that sex-reversed giant freshwater prawns, or neo females, are able to spawn larvae. These cross-bred larvae, which are all male, will be reared to the postlarvae phase before being released into ponds. In this regard, all male seed production technology brings immense economic benefits to farmers, thereby increasing the yield of giant freshwater prawns in Malaysia.