HATCHERY MANAGEMENT TECHNIQUES IN MARINE FISH CULTURE DEVELOPMENT
Field Document 1
PEOPLE'S REPUBLIC OF CHINA
A report prepared for the project
Development of marine culture of fish
Consultant (Hatchery Management)
This report was prepared during the course of the project identified on the title page. The conclusions and recommendations given in the report are those considered appropriate at the time of its preparation. They may be modified in the light of further knowledge gained at subsequent stages of the project.
The designations employed and the presentation of the material in this document do not imply the expression of any opinion whatsoever on the part of the United Nations or the Food and Agriculture Organization of the United Nations concerning the legal or constitutional status of any country, territory or sea area, or concerning the delimitation of frontiers.
FOOD AND AGRICULTURE ORGANIZATION OF THE UNITED NATIONS
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1. INTRODUCTION AND TERMS OF REFERENCE
2. DEVELOPMENT OF INFRASTRUCTURE AND FACILITIES
3. LARVAL FEED DEVELOPMENT
3.1 Criteria for larval feed selection
3.2 Mollusc larvae as primary feed for fish larvae
3.2.1 Mollusc larvae
4. HATCHERY MANAGEMENT
4.2 Selection of suitable broodstock
4.3 Broodstock management
4.4.1 Artificial fertilization
4.4.2 Induced spawning by hormone injection
4.5 Fertilization and incubation
4.6 Larval rearing
Appendix 1: ITINERARY AND LIST OF PERSONS MET
LIST OF FIGURES
1. Layout of hatchery
2. Water system
The Government of the people's Republic of China, assisted by the United Nations Development Programme and the Food and Agriculture Organization of the United Nations, is engaged in the project Development of marine culture of fish (CPR/31/014), whose main objectives are to develop the culture techniques including seed production of marine finfish in the coastal areas of China.
As part of the project operations, FAO assigned Mr Pinij Kungvankij as hatchery management consultant from 10 to 23 January 1988 and 29 January to 12 February 1983. The original terms of reference were as follows:
follow up and ensure the proper culture of desirable food organisms (algae, rotifers, brine shrimps, etc.) required for hatchery operations, especially for grey mullet;
acquire and ensure that a continuing supply of pure culture of the appropriate organisms (algae) is available for the station;
follow up the mass culture of desirable hatchery food organisms and pursue training of project counterparts.
ensure that the operations of the grey mullet hatchery are carried out properly;
train counterparts in the different aspects of hatchery operations;
coordinate his work closely with the other specialized consultants, in order to attain maximum efficiency in the management of the hatchery;
prepare a report of his assignment with emphasis on the operation of the grey mullet hatchery.
Although the existing hatchery and the support system for live organisms in Yantain are well developed, improvement is needed for the efficient implementation of the finfish programme, especially the mass seed production of marine finfish in the future.
Recommendations for improvement are outlined below:
a) Broodstock development tank
Modifying one 660 m outdoor concrete tank at the seafront for holding the broodstock in addition to the existing cages.
Dividing the tank into 4 equal compartments with polyethylene netting and wooden frame.
Installing one unit of 4-inch diameter pump at the edge of the tank to facilitate daily water changes at 50–60% per day.
Providing the tank with 1 unit of 2-inch air blower for water circulation and aeration.
b) Hatchery and nursery complex
The existing holding tanks in the hatchery are large (20–40 m3) and deep (2 m), and are suitable for broodstock conditioning, gonadal maturation trials and spawning tanks. Outdoor concrete tanks are suitable for live food organism production.
It is essential to develop the 150 m unused land adjoining the existing hatchery into a larvae-rearing and nursing complex, which should consist of 20 units of 1 m3, 20 units of 2 m3 and 10 units of 4 m3 fibreglass tanks for larval-rearing purposes.
The layout of the hatchery is shown in Figure 1.
c) Water intake system
Since the hatchery needs a large quantity of seawater, it should have its own pumping system.
Two types of water-intake systems are recommended:
Pumping seawater directly from the sea.
Pumping seawater through sump pit.
d) Water supply system
Although the seawater in front of the hatchery is very clear, filtered seawater is necessary for larviculture. The layout of the water system is shown in Figure 2. Unfiltered seawater will be used for the maturation and broodstock tanks and filtered seawater for larval-rearing.
One of the key factors to ensure success in marine finfish hatchery operations is the timely supply of the necessary food organisms in sufficient quantities. Ways of assuming continuous sources and mass production techniques are discussed below:.
Feeds suitable for fish larvae are characterized as follows:
they should be accepted by the fish.
the feed should be of a size which can be eaten easily by the larvae.
the feed should have high dietary value especially in highly unsaturated fatty acids (HUFA), essential to the growth and survival of the larvae.
the feed should be easy to mass-produce in large quantities.
The larvae of certain molluscs are attractive as a first feed for brackishwater and marine fish larvae because of their availability and small size. The most commonly used are the trocophore larvae of oysters and mussels.
Trials were conducted on induced spawning of green mussels and scallops. Both mussels and scallops were spawned after temperature shock treatment which resulted in the mass production of mollusc larvae for marine fish larvae throughout winter.
Many culturists engaged in the mass production of brackishwater and marine fish larvae believe that the presence of phytoplankton in the rearing tanks is beneficial to the whole rearing procedure. Apart from serving as direct feed for fish larvae and zooplankton, phytoplankton probably plays a role in stabilizing the rearing environment through the removal of metabolites or the supplementation of necessary marine vitamins or amino acids in solution. Phytoplankton apparently acts as the “conditioner” of the rearing system.
Chlorella, Tetraselmis and Isochrysis culture techniques were introduced and discussed.
The rotifer, Brachionus plicatilis, is generally used as the first food for larvae which are too small to begin feeding on brine shrimp nauplii. Brachionus plicatilis is capable of satisfying the nutritional needs of many different species primarily because it provides the developing fish larvae with a wide range of food size (approximately from 30 to 300 mm), if allowed to reproduce in the rearing tanks. Rotifers could be easily mass-produced in hundreds of millions in the hatchery using cultures of unicellular algae as food. The particular species of algae used are carefully selected to ensure the correct biochemical composition of the rotifers before they are fed to the fish larvae. The nutritional quality of rotifers fed with marine Chlorella is believed to be much better than those fed with either freshwater Chlorella or baker's yeast (Watanabe et al., 1978).
Culture methods for mass-production of phytoplankton and Brachionus culture are detailed in the “Guide to the Production of Live Food Organisms” to be issued shortly as Field Document 2 to this project; and Field Document 3 is the “Guide to Marine Finfish Hatchery Management”.
A sufficient supply of broodfish is essential for a successful induced breeding operation or artificial propagation. There are two sources of finfish broodstock: wild stock and those from ponds or cages. The disadvantages of wild stock is the uncertainty of capturing them, while the advantage of pond or cage reared broodstock is that they are already accustomed to culture conditions and consequently easier to develop into suitable broodfish.
Fish selected for broodstock should be fast-growing, active, and among the largest and strongest individuals of their age group, and free of parasites and disease.
Gonad development is affected by nutrition (food) and environmental factors indicated below:
There is paucity of information on the nutritional requirement of broodstock and suitable practical diets. Standard practices for feeding broodstock are not well documented. At present, broodstock is fed following traditional or empirical lines. The formulated feed used are generally those commercially available as feed for rearing fish to marketable size.
Data accumulated to date indicate that poor nutrition can result in poor or negative reproductive performance and that lack of a vitamin supplement can affect sperm quality. Reliance on natural food may also lead to poor or variable reproductive performance. It has been shown that fatty acids, especially in the case of ovarian lipids, tend to utilize the highly unsaturated fatty acids.
One of the factors considered of great importance to the inducement of sexual matuation and spawning is photoperiod. Photoperiod manipulation is now being employed to alter the normal production of a cultured fish species, for example, mullet, rabbitfish, rainbow trout, tilapia, carp and catfish. The greatest advantage of altering the spawning time of the cultured species is the availability of fry for stocking in ponds, pens and cages throughout the year.
Water temperature is another important factor which influences the maturation and spawning of fish. Data accumulated to date show that the functional maturity in some species of fish is directly controlled by temperature; in others, the time of spawning is regulated by the day-length cycle, and occurs at the time when temperature is optimum for survival and food supply is adequate.
Some species of fish, e.g., salmon, migrate from the marine to the freshwater environment in order to spawn, while others, such as eels, migrate from freshwater to the marine environment to complete their reproductive cycle. This definitely shows that salinity is related to maturation and spawning. Salinity may influence gametogenesis but probably does not function as a synchronizer for the timing of maturation.
- Other environmental factors
Aside from photoperiod, temperature and salinity, other less obvious factors may affect the maturation and spawning of broodstock, such as rainfall, stress, sex ratios, stocking density, isolation from human disturbance, dissolved oxygen, social behaviour of fish, heavy metals, pesticides, and irradiation.
At present, two major techniques are employed in the mass-production of marine finfish fry in Southeast Asian countries: artificial fertilization and induced spawning.
Spawners are caught in natural spawning grounds near the mouth of rivers or in saltwater lakes. The degree of maturity of the collected spawners is immediately checked.
The dry method of fertilization is normally used. The eggs are stripped directly from the female into a dry and clean container where the milt is added. A feather is used to mix the milt and eggs for about 5 minutes. Filtered seawater is added to the mixture while stirring, and it is then allowed to stand undisturbed for 5 minutes.
The fertilized eggs are then transported to the hatchery for subsequent hatching.
In induced spawning, the hormones used include the following:
SPH - acetone dried pituitary gland homogenate of coho salmon prepared by the British Columbia Research Council, Vancouver, Canada; 1 g powder contains 17.6 mg gonadotropin.
HCG - human chorionic gonadotropin, manufactured by Ayerst Laboratories, New York.
Before injection, HCG is dissolved in 3 ml of its accompanying diluent. The solution is then used to homogenize the acetone dried pituitary gland of salmon to be used for induced spawning.
Fishes with eggs of an average diameter equal to or more than 0.65 mm are induced to spawn by injecting hormones intramuscularly a few centimetres below the dorsal fin. In the first injection, the fish is given a combination of 10 mg SPH/kg body weight + 1 000–10 000 IU HCG/kg body weight. In the second injection, the fish is given a combination of 10 mg SPH/kg body weight + 2 000–20 000 IU HCG/kg body weight. Injections are administered intramuscularly a few centimetres below the dorsal fin after which the fish is completely anaesthetized by immersing it in seawater containing 100 ppm 2 - phenoxyethanol. The time-interval between injections is 24 hours for wild milkfish. This interval was selected to ensure that final maturation of eggs is completed before the fish dies or before the eyes of the breeders are completely covered with a white opaque substance.
Usually, only two injections are needed to induce both captive and wild adult fish to spawn, as long as the dosage and time-interval mentioned above are respected; however, badly injured fish may need a third injection. In such cases, the dose used in the third injection is that of the second injection. When a third injection is necessary, the fertilization and hatching rates are usually very low.
The fish that are induced to spawn by hormone injection will be ready to spawn within 9–12 hours after the final injection. The schedule of injections for subsequent spawning must be synchronized with the natural spawning time of the fish which occurs in late evening between 18.00 and 24.00 h. On the other hand, with the stripping method, it is still necessary to extract the eggs from gonads by cannulation and examine them under microscope. The fish has spawned only if at least 40% of the eggs are transparent.
Stripping is always done by gently pressing the abdomen with the thumb and forefingers, beginning to apply pressure just foreward of the genital pore. The eggs are fertilized immediately after stripping, using the dry method, the milt being hand-stripped from the hormone-treated male.
The eggs and milt are mixed gently but thoroughly using turkey feathers. After at least 3 minutes, seawater (34 ppt) is added to the mixture while stirring it. After another 3 minutes, the fertilized eggs are transferred in a scoop net (mesh size = 500 micron) and washed thoroughly with seawater isohaline in the incubation tanks. The incubators are strongly aerated to prevent the eggs from sticking together. The eggs are incubated at ambient temperature ranging from 25° to 30°C and at a salinity of 34 ppt. Six hours after the start of incubation, dead eggs are removed from time to time by stopping the aeration for about 5 minutes. Fertilized eggs float in seawater with a salinity of at least 34 ppt while unfertilized eggs sink.
Larvae of red seabream and black seabream were used to demonstrate the larval-rearing technique at the Centre.
The rearing tanks are made in plastic in a circular shape. Volume ranges from 1 to 10 m. The tanks are usually protected from sunshine and heavy rain.
Five hours before hatching, the developing eggs are transferred to larval-rearing tanks. The tanks are gently aerated. The larvae start to hatch 16–25 hours after fertilization, depending on the temperature and species. The usual stocking density of developing eggs is 100–200 eggs/litre.
Good quality seawater at 30–31 ppt is required for larval-rearing. Water temperature is also important and should range from 26° to 28°C to promote fast growth of larvae.
Larva, tanks are prepared one or two days prior to the transfer of newly-hatched larvae. Filtered seawater is added to the tanks and very mild aeration is provided. After stocking, unicellular algae (Tetraselmis sp. or Chlorella spp.) are added to the tank and maintained at a density of 8–10 × 10 or 3–4 × 10 per ml for Tetraselmis sp. and Chlorella spp. respectively. These algae serve a dual purpose: as a direct food to the larvae and other rotifers and as a water conditioner in the rearing tank.
The day following stocking, the bottom of the larvae-rearing tank should be cleaned, and every day thereafter. This is done by siphoning off unfertilized eggs, faeces, dead larvae and uneaten food accumulating on the bottom of the tank. About 20% of the tank water is changed daily for the first 25 days of the rearing period, then increased to 40–60% per day for the remaining culture period. Since seabass can also be cultured in freshwater, it is recommended to reduce the salinity of the rearing water when the larva is still in the hatchery, before it is transferred to the freshwater environment. Beginning with the twentieth day, salinity can be reduced gradually until a freshwater condition is reached on the twenty-fifth day.
The problems and prospects of programme implementation are summarized below.
The existing facilities both in Yantain and Qidong Research Station, although in need of improvement, are sufficient to implement project activities.
The main problem at Yantain is an insufficient supply of spawners. In Qidong, water supply is the major difficulty, even though the hatchery is located close to the Yellow Sea (during low tide there is about 5 km of mudflats).
Although activities on seed production of mullet are still in the experimental stage, other results have been achieved, such as establishment of fish hatchery, culture of mullet, development of a functional core staff, up-dating and modernizing the techniques through the use of new equipment.
The staff of the centre lack practical experience in commercial-scale seed-production; most of them were trained abroad but mostly at an academic level.
The implementation of the project involved many consultants all of whom visited the centres on short-term assignments. Their various suggestions and recommendations could be confusing to the local staff.
Although the immediate objectives of the project have been achieved, technical assistance should be extended. Much work is needed in the second phase to achieve the mass seed production of marine fish; the technology involved should be adapted to suit local conditions and disseminated to the farmers through training.
However, for the benefit of the Chinese Government, and to fully utilize the equipment and manpower, the project should include studies on induced breeding of other economically important finfish species, since the spawning seasons differ from one species to auother. The assignment of an international expert to work full time in the field with the local staff would be useful.
Existing facilities, especially the hatchery and nursery system, should be further improved in order to facilitate the Centre's mass production of marine fish fry. The 150 m2 unused land adjoining the existing hatchery should be developed into the nursing area to accommodate the fibreglass nursery tanks which have been ordered by FAO/UNDP.
The existing hatchery facilities will be used for maturation and spawning trials.
The 660 m2 outdoor concrete tank at the seafront should be modified to maintain the broodstock including division of the tank into four equal compartments of polyethylene netting with wooden frame. The advantage of this tank is that the fish can be reared the whole year round without risking damage by the typhoons. Broodstock of economically important species is needed to stock the tank, one species per compartment.
An inter-disciplinary and team approach should be adopted to implement the project activities instead of having one person in charge of one species. Since there are many interdependent factors, a number of parameters should be simultaneously studied, in order to obtain a valid result and to fully utilize the available facilities and manpower.
Since the project is oriented towards production, study tours and training of local staff should be emphasized only in related fields. Staff will thus become informed of the status of the industry in other countries, advances in marine finfish culture in general and marine finfish seed production in particular.
To facilitate transport a project vehicle is essential.
Fig. 1 Layout of hatchery
Fig. 2 Water system
|10 January||Departure from Bangkok for Beijing|
|11 January||Briefing FAO headquarters (Mr L.I.J. Silva, FAOR; Mr Tessel, Programme Officer; Mr Fugusho, Hatchery Management Expert, CPR/81/014). |
Meeting with Mr Jia Jiansan, Project Director
|12 January||Arrival Shen Zhen|
|13 January||Development of Marine Culture Project site, Yantain, meeting with staff, Inspection of facilities|
|14–23 January||Engaged in specified project work. Further meetings and visits in the area were arranged|
|20 January||Visit to Fisheries Research Station of China, Academy of Science and Breeding Centre of Pearl River Fisheries Research Station at Chong San|
|22 January||Participation in Tripartite meeting|
|23 January||Return to Bangkok|
|30 January||Arrival at Hong Kong|
|31 January||Meeting with Messrs Chen Foo Yen and Methew Chow|
|1 February||Meeting with Hong Kong's fish-farmers concerning broodstock of grouper, and departure of equipment procurement for Shen Zhen|
|2–6 February||Project site|
|7 February||Departure Shen Zhen for Guangzao|
|8 February||Meeting with Nanhai Fisheries Research Institute. Departure for Shanghai|
|9 February||Departure for Nan Tong, Qidong|
|9–11 February||Departure for Shanghai.|
|12 February||Departure for Guangzao|
|13 February||Departure for Hong Hong and Thailand|
LIST OF PERSONS MET
FAO Representative's Office
Mr L.I.J. Silva, FAO Resident Representative
Mr J. Tessel, FAO Programme Officer
Mr Fugusho, Hatchery Management Expert, CPR/81/014
Fishery Office, Beijing
Mr Jia Jiansan, National Project Director (NPD)
Yantain Fisheries Research Station
Mr Yu Mainyu, Deputy NPD
Mr Zhang Dan, Section chief of fish culture
Mr Lee Jia Tear
Staff of finfish culture section