Artificial propagation of bivalves:
Techniques and methods
UNDP/FAO REGIONAL SEAFARMING DEVELOPMENT AND
DEMONSTRATION PROJECT (RAS/90/002)
National Inland Fisheries Institute
Kasetsart University Campus
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LIST OF FIGURES
LIST OF PLATES
2.3.1 Seawater system
2.3.2 Tanks and vessels
2.3.3 Sieves and plungers
3.0 ARTIFICIAL PROPAGATION
3.1.2 Collection sites
3.1.3 Transport and handling
3.2 Conditioning of broodstock
3.2.2 Supplemental feeding
3.2.3 Gonad maturation
3.3.1 Mass spawning
3.3.2 Individual spawning
3.3.3 Gametocyte suspension
3.5 Determination of egg numbers
3.6 Placing the egg in culture vessels
3.8 Larval development
3.9 Culture vessel management
3.9.1 Culture medium changes
3.9.2 Density control and grading
3.11 Rearing of early spat
3.11.1 Up-welling system
3.12 Preparation of spat for on-growing
3.12.1 Nursery plots
3.12.2 Outdoor up-welling system
4.1 Larval diseases
4.4 Disease treatments
4.4.1 Ultraviolet light sterilization
4.4.2 Antibiotic treatment
4.4.3 Chemical sterilization
4.5 Disease prevention
5.0 PRINCIPLES AND TECHNIQUES OF PHYTOPLANKTON CULTURE
5.1 Algae species
5.2 Principles of culture growth
5.3 Media preparation
5.4 Culture system configuration
5.5 Monitoring culture growth
5.6 Large volume cultures
1 (A) Sub-sand seawater extraction and (B) surface seawater intake for hatchery use.
2 Home made hatchery sieves and plunger.
3 Oyster broodstock holding facilities. (A) Net cage seed and (B) pearl net. Both structures are used to hold oyster broodstock in their natural environment, either suspended from a floating structure or (A & B) or raised above the sea bottom on a rack system (A).
4 Bivalve molluscs flow-through conditioning unit. (A) Seawater header tank, (B) broodstock holding troughs, and (C) water drainage unit.
5 Collection of gametes for determining the ripeness of bivalve broodstock. (A) The selected specimen is either sacrifized or the (B) hole-method is applied to avoid killing the bivalve. (Source: Castagna and Kraeuter, 1981).
6 Preparation of a sperm and/or egg suspension. (Source: Castagna and Kraeuter, 1981).
7 Collection and determination of the number of fertilized eggs by evenly suspending them through the up-and-down motion of the plunger. (Source: Castagna and Kraeuter, 1981).
8 Developmental stages of an oyster larva: (1) fertilized egg, (2) early cleavage, 4-cell stage, (3) Morula stage, (4) ciliate trochophore, (5) Veliger and (6) Straight-hinge larva. (Source: Castagna and Kraeuter, 1981).
9 Seawater change of a bivalve larval culture vessel. (Source: Castagna and Kraeuter, 1981).
10 Separation of bivalve larvae by size. The larvae are rinsed through a descending sized series of sieves. (Source: Castagna and Kraeuter, 1981).
11 Indoor fibreglass up-welling tank. (A) Seawater reservoir vessel and (B) up-welling tubes.
12 Schematic drawing of an up-welling tube (A) with a meshed bottom (B), water outlet (C), and water flow control valve (D). The up-welling tubes are contained in a fibreglass tank usually placed above the reservoir tank (E).
13 (A) Lantern net and (B) pearl net typically used for the intermediate culture of scallop spat.
14 Land-based nurseries for rearing of juvenile bivalve spat. (Source: CNEXO, 1983).
15 Passive flow (A) and active flow (B) up-flow systems. (Source: Manzi, 1985).
16 Schematic diagram of the Milford and wells-Glancy methods of bivalve larval culture. (Source: Manzi, 1985).
17 (A) Typical growth curve of a phytoplankton culture, and (B) the relationship between number of cells in the inoculum and Lag time.
1 Oyster broodstock conditioning tanks. Visible in the foreground are two troughs placed in parallel and in the background one header tank and two tanks filled with algae.
2 Oyster larvae rearing tanks. Bivalve hatchery at the Brackishwater Station in Prachuab Khiri Khan in Thailand.
3 Oyster broodstock holding netcage.
4 Oyster broodstock holding pearl nets.
5 Histological sections of mature gonads of a (A) female and (B) male carpet clam, Tapes semidecussatus. (Source: Lovatelli, 1985).
This technical paper was prepared as part of the Mollusc-Shellfish Culture Course of the 7th NACA Training Course for Senior Aquaculturists in Asia and in the Pacific. This 12 month course commenced in March 1988 and was held at the NACA Regional Lead Centre of the Philippines in Tigbauan, Iloilo.
The aquaculture industry among developing Asian and Pacific countries has been growing considerably within the last decade, particularly in the mollusc culture sector. Asia is the most important continent in the world in terms of mollusc landings from culture practices followed by Europe and North America. The landings for the three continents in 1985 were 2,094,913 MT, 591,476 MT and 176,810 MT respectively, which accounted for 72.6%, 20.5% and 6.1% of the year's total production.
The bivalve groups which are widely harvested from natural fisheries or cultured in the region belong to the families Ostreidae, Mytilidae and Arcidae, and compared to the above, only few gastropods are important, mostly collected from natural fisheries. Among the latter group, abalones are certainly the most important, as they are highly valued as a food item and therefore highly priced.
The shellfish industry, in particular the shellfish culture sector offers great potential in many countries in Asia and Pacific for increasing domestic consumption and foreign exchange earning from export. In order to realize this potential, developmental programmes have been launched in several countries and some have achieved good results in terms of species cultured, production and export. However, the industry is facing a number of problems and constraints which vary in magnitude and severity according to area and country. The problems affecting the development of this industry may be categorized into three major groups: 1) environmental, 2) biological and 3) social.
* Mollusc Expert, FAO/UNDP Regional Seafarming Demonstration and Development Project (RAS/90/002), Kasetsart University Campus, Bangkhen, Bangkok, Thailand.
Environmental constraints include naturally occurring phenomena (e.g. salinity, temperature fluctuations, etc.) or those related to the direct or indirect effects of man's activities. Generally, the most evident and rapid factor causing environmental deterioration is pollution from either inorganic or organic substances. Typically the most fertile grounds for both capture and culture mollusc activities are intertidal areas, estuaries and shallow areas along the coastline. Unfortunately, these are the areas which are often more affected seriously by environmental pollution due to land runoff or direct discharge.
Biological constraints are numerous and variable. In mollusc culture one major constraint is the lack of seedlings, as well as the limited suitable culture grounds. Another serious problem which occasionally affects the industry is the occurrence of red tides which renders mollusc inedible due to the accumulation of toxic substances. Other problems may be related to adverse weather conditions which can cause serious losses to both capture and culture fisheries.
Social and institutional constraints which are affecting the industry are also numerous and vary from country to country. The lack of trained personnel in some countries is at present the major problem even though potentially the country has rich natural resources. The limited demand of a commodity, like molluscs in general, due to culture-related preferences as well as health considerations is also a limiting factor in the development of this industry.
From a survey conducted by the Regional Seafarming Project in 1988 (Working Paper NACA-SF/WP/88/4 entitled “Status of mollusc culture in selected Asian countries”), the limited seed supply appears to be the most serious constraint, followed by the lack of trained personnel and poor quality control. All the listed constraints are interrelated and in order to aid the development of this industry a multi-disciplinary approach needs to be adopted.
In order to further expand the mollusc culture industry in the region in the future it will be necessary to solve the problem of limited seed supply. This can be tackled either by artificially producing spat through hatcheries or by improving the techniques aimed at the collection of spat from the wild.
The present Working Paper covers various technological aspects of bivalve artificial propagation. Information on hatchery design and equipment, broodstock management and conditioning, spawning techniques, larval and spat rearing, disease prevention and treatment, as well as on the principles and techniques of phytoplankton culture is provided.
For further detailed information the list of References on page 50 should be consulted. The papers by Manzi (1985) and Castagna and Kraeuter (1981) are particularly relevant.