To establish and maintain pearl oyster hatchery involves a considerable amount of time and money both into equipment and staff. At present, pearl oyster hatchery requires monospecific unicellular algal cultures because of the herbivorous filter feeding mechanism of the animal. Pearl oyster hatchery requires practical knowledge and experience both in handling target animals and micro-algae culture, which can normally be achieved through many years of painstaking training processes. This short-term demonstration and training project was conducted for the officers of the Ministry of the Kingdom of Tonga between 6th April and 18th May, 1999. The aim was to offer basic knowledge on micro-algae culture for pearl oyster hatchery operation, as well as hatchery operation of the blacklip pearl oyster, Pinctada margaritifera, and the Mabe pearl oyster, Pteria penguin. The emphasis was particularly placed on how-to simplify procedures and minimise time spent on micro-algae production whilst enabling larval and spat rearings to be conducted with a minimum number of personnel. The TOR given for this consultation is attached as Appendix 3.1.
The pearl oyster hatchery production manual was presented together with various memos and notes prepared for the demonstration and training. Refer to Part II for the manual.
Refer also to Travel Diary (Appendix 3.2) which summaries a detailed daily activity during the present work performance in Tonga.
This demonstration and training project was funded by the FAO South Pacific Aquaculture Development Project II (SPADP). The author would like to express his sincere thanks to Mr. Hideyuki Tanaka, Chief Technical Adviser of SPADP and Mr. Ulunga Fa'anunu, Officer-in-charge, Nuku'alofa, Ministry of Fisheries for their invaluable support throughout this project. Also, support from the staff of the Ministry of Fisheries was greatly appreciated.
There was an infrastructure at the Fisheries Division, Nuku'alofa, which had not been designed specifically for the pearl oyster seed production, and most of the necessary equipment and materials for the pearl oyster hatchery had not been prepared before the arrival of the consultant. Therefore, certain modifications of the system, customizing equipment and alternative methodologies were needed to carry out the present work for pearl oyster hatchery demonstration and training. Shortage of equipment and materials were compensated by available materials, mainly temporary use of ongoing JICA Project, and day-to-day careful handling. Schematic diagrams of the pearl oyster seed production system at the Fisheries Division are shown in Figures 1, 2 and 3.
Three rooms at the Fisheries in Nuku'alofa were modified and were temporarily used for the demonstration and training, one of which was airconditioned and was designated as a micro-algae culture room. The spawning room of the ongoing JICA Project (green snail) was temporarily assigned as the room for the spawning and larval rearing of the pearl oysters and thus required the following modification:
Seawater supply system was modified from the existing supply line, installed an additional filtration system (ie. 25μ, 1μ and 0.5μ cartridge filters, UV sterilizer, and further 0.5μ filter) for micro-algae culture, spawning induction and larval rearing of the pearl oysters (Pinctada margaritifera and Pteria penguin).
Figure 1. Schematic diagram of pearl oyster seed production system (spawning and larval rearing room) at Fisheries Division, Nuku'alofa.
Figure 2. Schematic diagram of pearl oyster seed production system (preparation room)
Figure 3. Schematic diagram of micro-algae culture system at Fisheries Division, Nuku'alofa
The air supply system was diverted from the existing air supply line of the JICA Project. Freshwater was supplied from a rain water tank, pressurized by pump and passed through a 1μ cartridge filter before use for washing and rinsing of laboratory equipment and larval rearing tanks.
The floor of the room was covered with plastic mesh sheet to protect polycarbonate tanks and to avoid contamination without direct contact with the existing cement floor.
All the tanks and most of the laboratory equipment, such as a UV-steriliser, autoclave, filter housings, filter cartridges, airhose and other laboratory equipment, were temporarily borrowed from the JICA Project.
The preparation room was modified from an equipment storage room between the micro-algae room and spawning room, accommodated a work bench with microscope and other laboratory equipments, drying bench, washing bench and sink, and an autoclave.
When the consultant arrived with the micro-algae stock culture at the Fisheries Division, the construction of micro-algae culture room was still in progress and it took another 10 days to become operational for the demonstration and training. Certain modification and alternative methods were applied for the preparation. Micro-algae culture room was airconditioned to maintain the room temperature at 21–22°C artificial lighting with control 12L - 12D light-dark period was used for the synchronous micro-algae culture. All the culture media were sterilized with an autoclave for aseptic monospecific culture. Sterilized plastic syringes with cotton were used as an alternative for bacterial air vent for each aerobic culture. All the stock culture were supplied by the Micro-algae Section of the Fiji Fisheries. Some species had died shortly after arrival in Tonga and some were mislabelled with wrong species, particularly one of the Cheatoceros species had been labelled as Pavlova lutheri. In addition, all the stock culture had no certification of axenic culture and had also been badly contaminated, making it unsuitable for aseptic stock culture When stock culture was actually commenced, only 3 species were selected for the present demonstration and training (i.e. Cheatoceros mulleri, Tahitian clone of Isochrysis sp. and Tetraselmis suesica). Refer to Figure 3 for a schematic diagram of the micro-algae culture room and also refer to the micro-algae culture section of the hatchery production in Part II.
It should be noted that most of all the laboratory equipment, including glassware, microscope, culture tanks, water filters, seawater and air supplies, mesh screen and autoclave were temporarily borrowed from the JICA's ongoing project.
Practical techniques of micro-algae culture for pearl oyster hatchery, including culture media and equipment preparation, aseptic monospecific techniques for stock culture, high density culture and mass culture, sampling and counting of micro-algae, estimating cell density, and computing feed amount for pearl oyster larvae, were demonstrated for the officers of the Fisheries Department. “Hands-on” micro-algae culture training was conducted for the two Fisheries officers and other participants during the assignment in Tonga. The culture technique was also demonstrated to a member of Japan Overseas Cooperation Volunteers (JOCV) of the Vava'u Fisheries who participated later in the training. Before commencing the training, the system modification and construction for micro-algae culture were also demonstrated. Refer to the travel diary (Appendix 3.2) for detailed training schedule and activity. In addition, a manual of micro-algae culture for pearl oyster hatchery production was presented to the participants, of which emphasis was placed upon a practical technique for micro-algae culture in tropical island conditions. During the construction of the micro-algae room, nutrient media preparation was also demonstrated and concept and techniques of micro-algae culture for the pearl oyster hatchery purpose were explained to the fisheries staff. A simplified inoculation chamber (laminar-flow chamber) was also set up for stock and high density culture.
Transportation techniques, including preparation of equipment, packing and handling of broodstock, were demonstrated. In order to collect the broodstock of pearl oysters (Pinctada margaritifera and Pteria penguin), the consultant headed for Vava'u on 21st April and returned to Nuku'alofa on 23rd April with 30 broodstock (15 each male and female of Pteria penguin) by air. All the broodstock had been kept at experimental farm of the Vava'u Fisheries in Neiafu. However, there were no blacklip pearl oyster (P. margaritifera) kept at the Fisheries, and thus only “Mabe” pearl oysters (P. penguin) were available from Vava'u for this demonstration and training. During the stay in Vava'u, selection, sexing, handling and transportation of the broodstock were demonstrated on-site for the Vava'u Fisheries staff and other participants (e.g. JOCV). A plastic container (801 cooler box), which was borrowed from the JICA Project, was used for transportation of broodstock with ice pack to maintain the temperature at around 23–25°C inside the container. The broodstock were wrapped with wet towel to maintain saturated humidity inside the container. A total duration for the transportation from packing at Vava'u Fisheries to the broodstock holding tank at Nuku'alofa Fisheries was 5 hours.
On 24th April, 30 broodstock of Pinctada margaritifera were transported from a private pearl farm in Nuku'alofa by the ongoing JICA Project survey boat. Same container was used with same method without the ice pack. A total transportation time was 2 hours from the farm to the holding tank at Nuku'alofa Fisheries.
No mortality, except for those two species of pearl oysters sacrificed for artificial maturation and in vitro fertilization trials, has been observed until the end of the present work (18th May) after the transportation. Also, refer to the transportation of spawners section of the hatchery production manual (Part III section 2.2).
Various spawning techniques, including standard induction techniques, gonad stripping technique, artificial maturation of immature ova, artificial activation of non-mortile sperm, and in vitro fertilisation techniques, were demonstrated. Furthermore, incubation and counting eggs, collecting and counting newly hatched larvae, computation of feed amount, feeding techniques, and handling larvae were also demonstrated. Equipment making and preparation for the larval and spat culture were also demonstrated to the training participants. The participants were; 2 Fisheries officers, 1 JICA expert and 1 commercial pearl farm from Nukua'lofa, 1 Fisheries officer, 1 JOCV and 1 Vava'u Pearl Farming Association from Vava'u, and 2 Fisheries officers from Ha'apai). Refer to spawning and in vitro fertilisation section and larval rearing section of the hatchery production manual (Part III, section 3).
A small microalgae culture room was established at Fisheries compound in Sopu, Nukua'lofa, which proved to produce good quality micro-algae species for a small-scale pearl oyster larval rearing.
A high quality seawater supply system was set up for a continuous aseptic microalgae culture.
Basic knowledge of aseptic micro-algae culture for pearl oyster hatchery was acquired by the participants, and one of the Fisheries officer is now maintaining the algae and can prepare larval food for the pearl oysters.
Practical knowledge of spawning induction and in vitro fertilization techniques for pearl oysters were demonstration to the Fisheries officers.
The larvae of the both blacklip (P. margaritifera) and Mabe (P. penguin) pearl oysters were produced for the first time in the South Pacific during the outside spawning season, from the artificial maturation of eggs and artificial activation of sperm program.
A small-scale larval rearing system using 100 1, 200 1 and 500 1 tanks were set up for the demonstration and training.
Basic technique for the larval and spat rearing of the pearl oysters were acquired by the Fisheries officers.
It is not appropriate to conduct practical demonstration and training for the pearl oyster hatchery without completing larval and spat rearing program. It was difficult to conduct the demonstration and training smoothly without its own project equipment. (i.e. almost all the necessary equipment were temporarily borrowed from the ongoing JICA Project, which was a constant nuisance for this project and the JICA Project as well.)
It was not appropriate to perform practical training for Fisheries participants without positive motivation for the pearl oyster hatchery operation. Some participants from the outer islands seemed to join this demonstration just because of assignment from the Fisheries or seemed to be just for a holiday occasion, who did not join this program from the start date (8th April).
It is not appropriate to apply this kind of project for realization of commercial-scale hatchery spat production without proper planning (i.e. master plan, feasibility studies, pilot plan) and preparation (resource survey, equipment and material availability).
It seemed that there was a basic misunderstanding about pearl oyster hatchery operation. Lack of self-awareness of hygiene and daily equipment maintenance and preparation, and without strong motivation or dedication towards the work were the most fundamental problems here. The Pearl oyster hatchery operation is considered to be some of the most difficult aquaculture species for those who engage on-site, which involves not only basic aquaculture skills and knowledge but also requires delicate handling for algae culture and larval rearing, self-dedication, foresight, and flexible thinking. Without roster, overtime work, goal-oriented management, it was difficult to conduct day-to-day algae and larvae maintenance for the continuous demonstration and training.
Extensive resource survey for the pearl oysters (Pinctada margaritifera and Pteria penguin) should be done before planning commercial-scale hatchery operation. This is because hatchery operation requires constant supply of at least 100–200 broodstock (ideally 500 oysters) for the spawning induction program, and the assessment of resource (spawners) availability is essential to determine the scale of hatchery operation. Target locations will be Ha'apai Atoll, reef areas of Vava'u and Tongatapu.
It is not practical to establish a pilot hatchery within the compound of the Fisheries at Sopu because of various inconveniences as follows:
Water quality is not suitable for pearl oyster hatchery; contaminated with heavy silt and thus required a sediment/settlement tank and a high performance filtration system; water is pumped up from the shallow near shore lagoon area and adversely affected (rapid fluctuation of salinity and temperature) by the weather (i.e. rain).
Winter (from May to September) water temperature (22–17°C) in the rearing tanks is too cold to conduct pearl oyster larval rearing, which requires seawater heating system such as solar heating, heated water storage tank, or broad heaters with thermostat.
Seawater and air supply system had not been designed for the purpose of pearl oyster hatchery production but specifically designed for the giant clam, trochus and green snail programs (JICA Project). This indicates the need of additional seawater and air supply system. Seawater should be pumped up far away, at least 50m from the low tide mark, introducing to a silt settlement tank (20t ~) before leading to a storage tank. Air pump should be non-oil high pressure (e.g. “The Pump - 100 Outlets” capacity) for larval and spat culture system. A separate air pump should be installed in the algae culture system. Freshwater (rain water) tank is necessary with at least 5t capacity for single hatchery operation. The hatchery production will require a total maximum use of around 70t/day (20t/day for larvae, 30t/day day for spat and 20t/day for spawner conditions). Also, additional pressure pump will be required to pressurize seawater supply during the larval work.
Aquaculture section of the Fisheries is in use of ongoing projects (JICA project and Seaweed project) both outdoor, undercover and indoor areas. The indoor area requires extensive renovation for deteriorating ceiling and new water and air supply system. The two rooms used for the present demonstration is usually occupied by the JICA project's spawning and preparation rooms. The room set up for micro-algae culture training is not suitable for practical pearl oyster hatchery production because of small working space (only accommodates maximum of 4 × 30 1 mass culture tanks). Extensive renovation will be needed for ceiling (dust free ceiling), wall (complete separation from microscope room), air supply system (proper piping and separate air pump), culture shelves with stronger structure and water proof material or cover. A laminar-flow chamber should be renovated by new paint and surface cover and clean UV light fittings. The existing outdoor and undercover area is fully occupied by the JICA Project.
Almost all equipment belong to the ongoing JICA Project. The rest of the available materials and equipment can not be used permanently for the pearl oyster project. Additional new equipment and materials (refer the equipment list for the Vava'u pilot hatchery plan in 1998) will be needed. For the production of 50,000 ~ 100,000 spat (2–5mm size) from a single spawning run, at least 6×1,000 1 (or 12 × 500 1) larval and spat tanks will be required together with additional algae culture tanks (e.g.16 × 30 1, 4×200 1, 4×500 1). Also, 2~3 × 2t raceway tanks are to be designated as conditioning/holding tanks for spawners.
If there is no other choice but to establish pilot pearl oyster hatchery here, only available empty space is between the Fisheries Building and Training/Workshop Building. A new building structure would be needed to construct an undercover hatchery for spawning and larval rearing section with shade cloth enclosure. The concrete floor with good draining groove, new seawater and air supply system are also required. The area must be kept out of unnecessary entry by other staff, dogs and other animals.
It is the best to establish a pilot hatchery in Vava'u for hatchery spat production and staff “on-the-job” training.
For pearl farming prospect in the long run, the Mabe (P.penguin) pearl oyster is the best option for Vava'u by collecting natural spat. Also, the economical value of high quality Mabe is greater in future than that of the blacklip pearl oyster. It is imperative to conduct spat nursery culture training for establishing better management technique from the spat to the “mother-of-pearl” oyster. The hatchery production of the Mabe spat will be considered as a supplement to natural spat collection program depending on the demand from local Mabe pearl farms. If spawners of the silverlip pearl oyster are obtained, it will be worth to undertake hatchery operation to create a new pearl farming program.