LST in Chachoengsao Province has an ambitious plan for genetic improvement of the Thai strain after developing SPF broodstock and hatchery rearing for high survival and uniform all-male post larvae
By Zuridah Merican
Lukkungsetthi Company, or LST, in Amphoe Ban Pho, Chachoengsao Province, is the only broodstock multiplication centre and hatchery in Thailand able to consistently supply all-male giant freshwater prawn Macrobrachium rosenbergii post larvae for grow-out farms. At the AIT-organised international conference on the giant freshwater prawn, Giant Prawn 2023 (GP2023), in November, Somprasong Natetip, LST Founder and Director, described his journey since 2017. Next is to expand on his closed biosecure system for the genetic improvement of the Thai strain of this crustacean in terms of phenotype.
In Thailand, similar to other Southeast Asian countries, the giant freshwater prawn sector faces issues with supply of post larvae due to several failings, either because the larvae do not reach post larvae stages or there is a delay. Common too are the non-uniformity in post larvae size, low survival rates and incidences of white tail disease.
Challenges in grow-out ponds
Grow-out using the conventional post larvae will result in different proportions of the morphotypic stages of the male prawn: 5% blue claw, 20% strong orange claw and orange claw and 25% small males. Some 50% of the population are females, which grow slower than male prawns. This combination usually results in growth by hierarchy behaviour, low survival rates, slow growth and low average daily growth, high feed conversion ratios (FCR) and more females with lower growth rates than males. Some of these have poor market prices. Khun Somprasong also added that there is a demand for prawns with big tails, short heads and small and orange claws in Thailand.
Consequently, farming an all-male population is preferred. Males generally exhibit faster growth rates and are 2–3 times bigger and heavier than females of similar age. The traditional practice is manually selecting males for culture during the grow-out, but it is labour-intensive and generally unsuccessful in producing an all male prawn monoculture.
Commercialisation of all-male technology in Thailand
In 2006, Dr Wikrom Rungsin at the Department of Zoology, Faculty of Science, Kasetsart University, developed the technology to produce all males of the Thai strain of M. rosenbergii using a neo-female technology. This is ablation of the androgenic gland in 45-day post larvae (PL45). The androgenic gland is essential for sexual differentiation in prawns and the development of male primary and secondary sexual characteristics (Tan et al., 2020). Done at the right time, this delicate procedure causes the post larvae to develop into neo-females with chromosomes ZZ. Neo-females are mated with local males to produce all-male progeny theoretically. Neo-females are males functioning fully as females.
As part of the “Talent Mobility” program of Kasetsart University, National Science Technology and Innovation Office of Thailand, LST is commercialising this technology. Dr Wikrom acts as a consultant at LST. Following a market survey and developing a vision for the freshwater prawn hatchery segment in Thailand, the company developed a prototype hatchery in 2017. However, for Khun Somprasong, it was not just adopting the process. It was more to do with the genetic improvement of the species.
It has developed closed biosecure systems for a breeding program, targeting the production of fast-growing all-male post larvae from specific pathogen-free (SPF) broodstock. Since 2019, LST has a nucleus centre comprising separate facilities for quarantine, maturation, spawning and genetics selection and breeding. Then, there is a broodstock multiplication centre and hatchery. Nursery and grow-out ponds complement these facilities to conduct field trials.
Samples were collected as founder stocks. One might think that large broodstock are required for good post larvae, but Khun Somprasong said, “It is only necessary to have a broodstock, even though small, which has been through the reproduction process until fertility is complete.”
The criteria for SPF status required assurance of the absence of 5 major pathogens over a two-year period. These included white spot syndrome virus (WSSV), yellow head virus (YHV), Macrobrachium rosenbergii nodavirus (MrNV) and extra small virus (XSV), both causative pathogens for white tail disease. There is also the monitoring for decapod iridescent virus 1 (DIV1) which has not been recorded in Thailand but is on the Department of Fisheries Thailand (DOF) monitoring list. “We cannot use live feeds for broodstock maturation to prevent contamination from pathogens,” said Khun Somprasong.
Essentially, the game changer for Thailand’s M. rosenbergii industry is the closed biosecure facilities to keep pathogens away and control rearing conditions.
Quality and uniform post larvae production
During a post-conference visit for GP2023 participants, LST hatchery staff explained some practices. At the pre- spawning stage, each male and female broodstock is held in one cubicle. In the mating tank, there is one male to 10 females. After moulting, prawns will mate very quickly; within a 15-minute interval, the females will allow entry of spermatozoa. Following hatching, nauplii are transferred into the closed indoor hatchery.
“We have developed the precise standard operating procedures to mass produce post larvae. We are proud that we can harvest nauplii daily, reach the post larvae stage in 14-15 days and complete in 4 days much faster than conventional post larvae produced with undomesticated broodstock. Our post larvae are of uniform sizes without going through a selection process. Post larvae are pathogen-free, and for every batch, larvae develop to post larvae well. We do not need to use antibiotics,” said Khun Somprasong.
In the hatchery, there is a well-controlled feeding regime. LST produces its own pathogen-free instar 1 artemia (500µ) which can be kept in ice for 48 hours. The first feeding of nauplii is with this artemia at 100g/million nauplii. In later weeks, larvae are fed egg custard (300µ) with added astaxanthin and artemia, alternated at specific intervals to prevent water pollution. The hatchery team discussed the sources of artemia available in Thailand with participants and their pros and cons. They also indicated that when using GSL artemia, each gram contains 250,000 to 260,000 cysts.
Post larvae are fed pelleted feeds. After PCR testing (PL4), they are sold to farmers and cultured in nursery ponds to gather growth performance data as feedback for the genetic improvement work.
Success rate in an all-male production
In the case of LST, the current success ratio is > 90% male progeny. In his presentation, Khun Somprasong showed how for some post larvae the delicate ablation procedures can fail, indicated by a white shadow in the gland of the head (Figure 1).
“In the pond, one can find this combination: >90% males, higher survival rates, fast growth with low FCR and ultimately higher profit margins with lower costs of production.”
Nursery and pond grow-out
Harvests at nursery level and grow-out ponds justified the progress with LST’s post larvae. In Table 1, Khun Somprasong explained the growth of PL4 in outdoor nursery ponds compared with conventional stocks of post larvae available in Thailand. While LST’s stocks grew to size 120-125/kg, conventional stocks grew 34% slower to reach only size 170-200/kg after 60 days when stocked at 19 PL/ ha (Table 1)
Field trials
Khun Somprasong described experiences in the field in the monoculture of his post larvae. This started with a nursery phase of 2 months to grow to 4g or 200-300 juveniles/kg. In the grow-out phase, the stocking was 7,000 to 10,000 juveniles/rai (1600m2). This translated to 5-6 juveniles/ m2. At days of culture (DOC) of 80-100 days, and after three times culling, the production totalled >2 tonnes/ha. (Related article: Polyculture of vannamei shrimp and giant freshwater prawn in Chachoengsao Province pages 22-23)
Into the future
In 2020, LST worked on increasing production, from 50 million post larvae in 2017 to 300 million post larvae in 2020. In 2021, in cooperation with Kasetsart University, the plans included building up more farms. Khun Somprasong is now looking at a corporate image for the company, increasing production and reducing production costs, in parallel to developing a full-fledged genetic centre for Thailand’s M. rosenbergii and investing around THB 100 million (USD 2.85 million). It already has the permit from DOF to export post larvae. Meanwhile, the R&D cooperation with Kasetsart and NRTC will continue.
References:
Kianann Tan, Huigong Jiang, Donghuo Jiang, Weimin Wang, Sex reversal and the androgenic gland (AG) in Macrobrachium rosenbergii: A review, Aquaculture and Fisheries, Volume 5, Issue 6, 2020, 283-288, https://doi.org/10.1016/j.aaf.2019.11.004.
Wikrom Rungsin, Natthapong Paankhao, Uthairat Na-Nakorn. 2006. Production of all-male stock by neo-female technology of the Thai strain of freshwater prawn, Macrobrachium rosenbergii. Aquaculture, Volume 259, Issues 1–4, 2006, 88-94, https://doi.org/10.1016/j.aquaculture.2006.05.041.
Somprasong Natetip, Intensive all-male prawn seed production in closed system commercial success of an improved giant prawn strain in Thailand. Presented at Giant Prawn 2023, November 27- 29, Bangkok, Thailand.
The article was published in issue January/February2024 AQUA Culture Asia Pacific
