Bivalve Hatchery Research Articles

Bacterial Population Association with Phytoplankton Cultured in a Bivalve Hatchery

Bacterial populations association with phytoplankton cultures used as food for bivalve larvae were enumerated and identified from their partial 16S rDNA gene sequences. Microalgae were provided from different European hatcheries during the larval production season. Average concentration (direct counts) of bacteria ranged from 1.3 x 10(5) to 5.3 x 10(8) mL(-1) while culturable bacteria represented from 10% to >60% of total bacteria. In most cases, three to six representatives of each type of colony were collected on solid medium. The identity of isolates from the same colony type was checked by two different randomly amplified polymorphic DNA (RAPD) typing methods, after which the 16S rDNA gene of one to three isolates by colony type were partially sequenced. Algae harbored a large spectrum of bacteria belonging to the alpha-Proteobacteria, beta-Proteobacteria, gamma-Proteobacteria, Cytophaga- Flavobacterium- Bacteroides (CFB) group, Actinobacteria, and Bacillus. Members of the Roseobacter clade and CFB group were the most abundant. In the majority of cases one strain constituted 50% or more of the culturable bacterial flora. About half of the isolates were common to two hatcheries or at least two microalgal cultures. Several isolates were closely related to bacteria associated with harmful dinoflagellates in culture. Thus, the algal cultures seemed to favor certain bacterial species which belonged to distantly separated groups. As some of them could disturb the development of bivalve larvae, the control of bacterial populations would undoubtedly make it possible to reduce larval losses in bivalve rearing.

Comparison of Three Culture Methods for the Intensive Culture of Northern Quahog Seed, Mercenaria mercenaria

AbstractA number of approaches have been utilized for growing bivalve hatchery seed (1 mm) to a size suitable for field planting (< 8 mm) but few have been directly compared. This study evaluated the growth and survival of northern quahog seed in three different culture systems and two different stocking densities. The three systems were: 1) a stacked‐tray unit with downward water flow; 2) traditional upweller culture units with water flowing upward without seed bed expansion; and 3) upweller culture units with water flowing upward at fluidization velocities to provide seed bed expansion. The two stocking densities were 1.0 and 3.0 g whole wet weight clam/cm2 respectively. During each trial period the seed clams were fed a 1% daily ration (% dry weight algae per wet weight clam per day) of the cultured diatom Chaetoceros muelleri. After 14 d of culture at the 1.0 g whole wet weight/cm2 stocking density, seed clams (4.4 ± 0.6 mm initial shell length) under fluidized‐flow condition exhibited better growth (0.54/d), and a greater final shell length (5.9 ± 1.0 mm). At the high density stocking conditions, after 28 d of culture, seed clams (4.2 ± 0.6 mm initial shell length) in the fluidized‐flow culture conditions again exhibited better growth rate (0.031/d) and a greater final shell length (6.0 ± 1.0 mm). The preliminary evaluation of fluidized‐flow for seed clam culture in land‐based nurseries indicates its potential as a suitable alternative to raceway, downwelling, or traditional forced‐flow culture methods.

Toxicity of bacteria towards haemocytes of Mytilus edulis

Haemocytes of Mytilus edulis, allowed to attach to the plastic surface of a tissue culture plate in the presence of haemolymph, were observed by time-lapse video recording. When bacteria were added at concentrations of 10 or 50 bacteria per haemocyte, certain bacterial strains caused rounding of the cells within 2–3 h. Haemolymph was necessary for the rounding to occur; if bacteria were added in sterile seawater there was no significant difference in the number of rounded cells between control and bacteria-treated cultures for up to 4 h. The haemolymph factor required for this activity was active at 1/64 dilution in seawater, was sensitive to trypsin treatment, and activity was halved on heating at 56 or 100 °C for 30 min. For the most toxic bacteria tested, Vibrio alginolyticus NCMB 1339 and Vibrio anguillarum A7, haemocyte cell rounding appeared to be induced by a very small number of bacterial cells. Bacteria-free culture supernatant of V. anguillarum 2981 induced rounding of haemocytes in a dose-dependent manner, with 50 % of cells being rounded at a dilution of approximately 1/500 of the culture supernatant. In a survey of 226 bacterial isolates, those isolated from incidents of disease in a bivalve hatchery were significantly more toxic towards haemocytes than bacteria isolated from hatcheries without disease or from turbot hatcheries.

Culture of Juvenile Atlantic Surfclams, Spisula solidissima solidissima and Spisula solidissima similis, in Forced‐Flow Upwellers in a Bivalve Hatchery in Coastal Georgia

AbstractFour experimental growth studies for juvenile Atlantic surfclams, Spisula solidissima solidissima and Spisula solidissima similis, under hatchery conditions were conducted in 10‐cm diameter forced‐flow upweller units. Experiments were designed to determine optimum food ration (2%, 5%, and 8% g dry weight of algae/g wet weight of clam), water culture temperature (20, 25, and 30°C), flow rate (2, 4, and 6 Lpm), and stocking density (7, 14, and 21 g wet weight of clams) for rearing juvenile clams in upweller units. Each experimental trial was performed for a 14‐d period. Nested Analysis of Variance showed that juvenile surfclams Spisula solidissima similis grew significantly faster at a temperature of 20°C and food rations of 5% and 8%. In all four experiments, clam mortalities were not observed except in the temperature experiment, where total mortality occurred for clams cultured at 30°C. Clam growth in biomass and size decreased significantly with increases in culture temperature. For Spisula solidissima solidissima, clam growth was significantly reduced in terms of size and biomass at a flow rate of 6 Lpm. No difference in size or biomass was determined between clams grown at a flow rate of 2 or 4 Lpm. Surfclams at the lowest stocking density of 7 g wet weight significantly increased more in net biomass compared to those at higher stocking densities. Clams were significantly larger in shell length when grown at the two lower stocking densities compared to those at the highest stocking density. Hatchery‐rearing protocol for juvenile surfclams is discussed.

Evaluation of microalgal clones for mass culture in a subtropical greenhouse bivalve hatchery: growth rates and biochemical composition at 30 °C

Eleven microalgal clones were screened for their ability to grow at temperatures of 30–35 °C as a preliminary test of their suitability for greenhouse mass culture in a bivalve hatchery located in the southeastern United States. Five potential candidate clones, Isochrysis aff. galbana (TISO), Isochrysis sp. (CISO), Chaetoceros muelleri (CHAET10), Tetraselmis suecica (TETRA1), and Ellipsoidon sp. (ELLIP1), were further characterized for growth rates and biochemical composition (particulate organic carbon and nitrogen, chlorophyll a, total protein, total carbohydrate, and major lipid classes) at various stages of batch culture at 30 °C. Experiments were conducted under two light regimes, which represent the approximate range of daily irradiance that can be achieved in the greenhouse mass culture facility. Only clone CHAET 10 showed good growth at 35 °C. Other clones may be suitable for mass culture at temperatures up to 32–33 °C. Total protein at 30 °C was highest for TISO and CISO. Changes in the relative proportions of protein, carbohydrate and lipid between batch culture phases were minor for the Isochrysis clones, while the proportion of carbohydrate increased in CHAET10 and TETRA 1 from exponential to stationary phases. Lipid production in clone ELLIP1 was strongly influenced by growth irradiance, with substantial production of triacylglycerols under higher light. The biochemical composition of microalgal clones, and hence the diet supplied to larval and juvenile bivalves, may be manipulated to some extent by control of the growth irradiance and the stage of batch culture at which the cells are harvested.

The economics of producing algae and bivalve seed in hatcheries

A computer program to estimate variable production costs in a bivalve hatchery was developed by using data from a working hatchery and from current literature. The empirical analysis focused on estimating algae costs to produce Atlantic oyster seed, because data on the algae process were more readily isolated from other hatchery processes and because feeding costs are recognized as a large proportion of total costs. Twelve simulations were made using different values for important parameters. Feed costs per bivalve were sensitive to the alternative specifications of feed cost functions, but not to assumptions about survival rates. To explore the implications of these feed cost simulations for the marketing of bivalve seed, total costs of production per bivalve were estimated on the basis of estimates of the proportion that feed costs are of total costs from an economic engineering study. Under optimistic assumptions, bivalve seed can be produced and marketed profitably. Within a given scenario, the “break-even” marketing period varied only by a week or two across the diverse assumptions made about the fraction that feed costs are of total costs.

Improvement of sea water quality by physical and chemical pre-treatment in a bivalve hatchery

The development to the veliger stage of fertilised ova of the Pacific oyster, Crassostrea gigas, was compared in raw natural sea water and in sea water pre-treated with various substances. Significantly higher veliger yields were obtained when the water was pre-treated with 1 mg l −1 EDTA. Combinations of EDTA and 20 mg l −1 sodium metasilicate, or 20 mg l −1 alumina, or 50 mg l −1 magnesium trisilicate or 150 mg l −1 Fuller's earth also enhanced development.

Bacteriological and physico-chemical analysis in a bivalve hatchery: Techniques and preliminary results

The bacteriological and physico-chemical methods used in the survey of a bivalve hatchery are presented and the preliminary results discussed. It was concluded that food, through its contribution of nutrient salts and bacteria, had a major influence on larval culture. The physico-chemical characteristics of sea water were not modified by heat or filtration treatments. The bacteria were not always eliminated from sea water by filtration and were sometimes more numerous after treatment. In effect, the larvae were raised in an artificial environment subject to marked fluctuations which had mechanical and biological origins. This survey must be complemented by a qualitative bacteriological study and the establishment of critical values for the physico-chemical parameters involved in the culture of these bivalve larvae.