CL 1
ESTACION, J., SOLIS, E. and L. FABRO
A preliminary study of the effects of supplementary
feeding on the growth of Tridacna maxima
(Roding) (Bivalvia: Tridacnidae).
1986 6 pp
Silliman Journal, vol. 33, nos. 1–4, 111–116
The effects of supplementary feeding on the growth of the giant clam Tridacna maxima was studied using Isochrysis galbana, Tetraselmis sp. and a mixture of both. Juvenile clams fed with the mixed culture had significantly higher growth rates, after the second and third months, followed by Isochrysis and Tetraselmis alone. Unfed clams supplied with filtered seawater had the lowest growth.
CL 2
ALCAZAR, S.N. and E.P. SOLIS
Spawning, larval development and growth of Tridacna
maxima (Roding) (Bivalvia: Tridacnidae).
1986 9 pp
Silliman Journal, vol. 33, nos. 1–4, 65–73
Adult T. maxima were successfully induced to spawn in the laboratory using macerated gonad in December 1984 and January 1985. Spontaneous spawning occurred in February and October 1985. Spawning can be induced in the morning as well as in the afternoon. Larvae were reared to the juvenile stage in larval rearing tanks and larval development monitored. A stereotype development pattern was displayed. Less than 1% of juveniles survived from eggs. Four-month-old juveniles placed in raceways provided with continuous flow of unfiltered seawater attain a mean shell length of 38.35 mm after 8 months, with an average monthly growth of 4.1 mm +- 0.8.
CL 3
ALCALA, A.C., SOLIS, E.P. and S.N. ALCAZAR
Spawning, larval rearing and early growth of Hippopus
hippopus (Linn.) (Bivalvia: Tridacnidae).
1986 9 pp
Silliman Journal, vol. 33, nos. 1–4, 45–53
The results of rearing laboratory-spawned eggs and larvae of the giant clam Hippopus hippopus (Linn.) in the laboratory are described. Veliger larvae reared at stocking densities of 1.2 to 5/ml and fed with the unicellular algae Isochrysis galbana and Tetraselmis sp. developed into 3–4-month-old juveniles. The survival rates of 3–4-month-old juveniles from veliger ranged from 0.03 to 2.13%. For successful mariculture, larval mortality rates must be reduced.
CL 4
ALCALA, A.C.
Distribution and abundance of giant clams (Family
Tridacnidae) in the south-central Philippines.
1986 9 pp
Silliman Journal, vol. 33, nos 1–4, 1–9
A population survey of giant clams (Family Tridacnidae) was conducted in certain coral reef areas of the Central Visayas, Western Visayas, Cagayan Islands and Palawan from February 1984 to October 1985. The largest species of Tridacna (T. gigas and T. derasa) were found to be either extinct or greatly reduced in numbers probably because of over collection. The smaller species of Tridacna, although of variable densities, appear to be holding their own in general. Hippopus porcellanus may also be endangered. The status of H. hippopus is uncertain, but it occurred at some reefs in the Central Visayas, Cagayan and Palawan regions.
CL 5
ALCAZAR, S.N.
Observations on predators of giant clams (Bivalvia:
Family Tridacnidae).
1986 4 pp
Silliman Journal, vol. 33, nos. 1–4, 54–57
Giant clams are now the subject of mariculture studies throughout the Indo-pacific region. One question to be answered before large-scale culture is attempted is the extent of predation in the natural habitats. This paper presents preliminary observations on predation on five species of tridacnids (Tridacna crocea, T. derasa, T. maxima, T. squamosa and Hippopus hippopus) in the laboratory and in nature.
CL 6
GWYTHER, J. and J.L. MUNRO
Spawning induction and rearing of larvae of Tridacnid
clams (Bivalvia: Tridacnidae).
1981 21 pp
Aquaculture, 24, 197–217
A new, reliable method of inducing spawning in Tridacna maxima, using freeze-dried gonad is described. A direct induction technique useful for underwater work is also presented. The effect of food supply on larval growth and metamorphosis was investigated and larval growth in the absence of particulate food is discussed. It is suggested that inclusions visible in the larval velum are symbiotic algae, which must have been acquired at the egg stage either before or during extrusion of eggs from the adult. The role of dissolved organic matter in larval nutrition is discussed. Settlement of pediveligers onto plastic panels was tested, and the substrate found to be acceptable to larvae as well as convenient for the culturist. Methods to improve juvenile survival are suggested.
CL 7
BECKVAR, N.
Cultivation, spawning, and growth of the giant clams
Tridacna gigas, T. derasa, and T. squamosa in Palau,
Caroline Islands.
1981 10 pp
Aquaculture, 24, 21–30
Larvae of the giant clams Tridacna gigas, T. derasa, and T. squamosa were reared in the laboratory, and juveniles were cultivated outdoors in a sunlit, flowing seawater system. Gametes were obtain from spontaneous laboratory spawnings and by induction of spawning with hydrogen peroxide. No supplemental food was added to the system. Laboratory reared T. gigas reached a mean length of 2.6 cm at 10 months post-fertilization; T. derasa were 1.1 cm mean lenght at 5 months; and T. squamosa were 6.7 cm mean length at 2 years. Field growth studies on clams, 12–25 cm long, predicted high projected growth/year: T. gigas grow 8–12 cm/year; T. derasa grow 3–6 cm/year; Hippopus hippopus grow 3–5 cm/year; and T. squamosa grow 2–4 cm/year. Instantaneous growth rates decrease with increasing length for each species. Mariculture and the seeding of overharvested reefs may now be examined for their feasibility.
CL 8
CRAWFORD, C.M., NASH, W.J. and J.S. LUCAS
Spawning induction, and larval and juvenile rearing
of the giant clam, Tridacna gigas.
1986 15 pp
Aquaculture, 58, 281–295
Specimens of Tridacna gigas were induced to spawn using intragonadal injections of serotonin. Some larvae were reared using conventional bivalve rearing techniques in 500-l tanks, with up to 40% survival to settlement after 7–8 days. Other bivalves were reared extensively from eggs added directly to raceways. There was heavy mortality at or soon after metamorphosis in all groups of juvenile clams and survival of juveniles from intensive larval rearing was less than 1% to harvesting at 5 months. Similar number of clams were harvested from raceways to which 4×10(5) intensively reared pediveligers or 2×10 (7) eggs (intensive culture) were added initially, yielding a total of ca. 6000 juvenile clams. Some juvenile clams were fed cultured microalgae for several months to supplement the nutrients obtained from their symbiotic zooxanthellae. These clams showed poorer survival than unfed clams, apparently because they were more overgrown by benthic algae. The distribution of the juvenile in the raceways at harvesting was not influence by water turbulence or shading, but growth rates were reduced by shading. Growth rates and densities of juveniles were much higher on textured than smooth substrates. Mass rearing methods used for bivalve mollusc larvae are appropriate to T. gigas larvae; however, the typical methods for bivalve nursery rearing are not readily applicable to giant clam juveniles. Further research is required on these methods and on factors affecting juvenile survival and growth.
CL 9
FITT, W.K., FISHER, C.R. and R.K. TRENCH
Larval biology of tridacnid clams.
1984 15 pp
Aquaculture, 39, 181–195
This paper describes research that attempted to address aspects of the larval biology of Hippopus hippopus and Tridacna gigas with an aim towards improving larval survival. The effects of larval density and exogenous food supply on survival and growth of tridacnid larvae was emphasized. The brief trochophore stage showed high mortality, but optimal survival was found at densities between 0.2–5 larvae/ml. Survival and growth rate of veligers were found to be optimal at densities of 0.2–10 larvae/ml. Control (unfed) veligers demonstrated high growth rates during the first half of the veliger stage, after which growth rates declined to zero, and mortality increased markedly. In contrast, veligers provided with particulate food (I. galbana, Tahitian strain) had significantly higher growth rates and lower mortality than controls. Phaeodactylum tricornatum is not an effective food for tridacnid larvae. Optimal growth and survival of veligers fed I. galbana occurred with algal densities of 10(40)-10(5) cells/ml. Dissolved organic nutrients in the form of vitamins and yeast extract enhanced veliger growth and survival. Symbiotic algae are not passed from one clam generation to another. Under experimental condition, veligers take all strains of Symbiodinium microadriaticum, but symbiosis is not establish until after metamorphosis.
CL 10
HESLINGA, G.A., WATSON, T.C. and T. ISAMU
Cultivation of giant clams: beyond the hatchery.
1986 5 pp
In: J.L. Maclean, L.B. Dizon and L. V. Hosillos
(Eds). The First Asian Fisheries Forum, 53–57
The article describes methods developed over a 5-year period for culturing tridacnid clams from seed size to sexual maturity in the natural environment. Design requirements for ocean-based nursery systems are reviewed and various culture option considered. Details are given for one proven method, a bottom-based system of modular nursery cages. To date, 2000 such units have been constructed and deployed at the Micronesian Mariculture Demonstration Centre giant clam farm in Palau. The basic nursery cage is a 60-cm square, molded plastic tray with an attached lid of plastic mesh. A layer of basalt chips or coral rubble added to the floor of the tray serves as ballast and provides a substrate for byssal attachment by the clams. The units are lightweight, stable, inert in seawater, easy to mass produce and effective in excluding most crustaceans, molluscan and teleostean predators. At the same time they allow acceptable levels of light penetration and water exchange. An analysis is given on materials and labour costs, performance in field trials, biofouling and projected lifespan. Guidelines are presented for selecting appropriate tridacnid culture sites in the natural environment and for deploying and maintaining the nursery cages on the sea bottom.
CL 11
GOULLETQUER, M.N. and M. HERAL
Production de palourdes Japonaises Ruditapes
philippinarum (Adams et Reeve) en bassin semi-ferme:
approche energetique et relations trophiques.
1988 18 pp
Aquaculture, 74, 331–348
The energy budget of Ruditapes philippinarum (Manila clam) and the carrying capacity of oyster ponds (‘claires’) were monitored during a breeding cycle. Unfavorable periods with negative meat production, associated with low food availability, were found during summer. At a rearing density of 85 individuals/m2 (biomass 1 kg/m2) growth and sexual maturation were delayed. This was related to depletion of available food in a semi-closed environment. There was permanent depletion competition between the multiplication of phytoplanktonic cells and their consumption (filtration) by the clam. Primary production and production of clam biomass were then restricted.
