Gary F. Newkirk

Evaluation of phytoplankton as diets for juvenile Ostrea edulis L.

Of 16 phytoplankton species tested as juvenile oyster diets, those superior to the reference diet Isochrysis galbana clone T-iso emerged with the following descending ranking: Chaetoceros gracilis Schutt, C. calcitrans Takano, Skeletonema costatum (Grev.) Cleve, Chaetoceros simplex Ostenfeld, Rhodomonas sp., and Thalassiosira pseudonana Hasle & Heimdal. The daily oyster growth rate with Chaetoceros gracilis was 1.5 to 1.8 times that with Isochrysis galbana clone T-iso. Biochemical analysis on some of the good and poor algal diets provided insight into the nutritional requirements of Ostrea edulis (L.) juveniles. Level of the essential fatty acids 20: 5ω3 and 22: 6ω3 and carbohydrate level are important factors in a good algal diet for O. edulis juveniles. Variation in the amino-acid composition among the seven algal diets analysed was small and did not explain the observed differences in oyster growth response with the diets. There was no clear trend between the protein level of the diet and the growth response of the oysters.

Growth of juvenile Ostrea edulis L. fed Chaetoceros gracilis Schütt of varied chemical composition

The chemical composition of Chaetoceros gracilis Schutt was altered by varying the nutrient conditions of the culture. The protein content of cells cultured in the complete f/2 nutrient medium (control) and the silicate-limited medium was similar, but cells from the nitrogen-limited medium contained ≈ 60% less protein. There was little change in amino-acid composition of cells from the three culture regimes. The lipid content of silicate-limited cells was more than twice that of either the control or the nitrogen-limited cells. The predominant fatty acids in the cells from all three nutrient treatments were 14:0, 16:0, 16:1ω 7, and 20:5ω3. The content of the essential fatty acid, 22:6ω3, in the control, silicate-limited, and nitrogen-limited cells was 0.23, 0.08, and 0.10 μg · (106 cells)−1, respectively. The carbohydrate levels of the silicate-limited and nitrogen-limited cells were, respectively, 1.6- and 3.2-fold higher than the control. The growth responses of Ostrea edulis (L.) juveniles fed the three cultures of Chaetoceros gracilis were a function of feeding ration. At high feeding ratios the highest oyster growth rates were obtained with the control C. gracilis diet. The relatively high level of the 22:6ω3 fatty acid in this diet is suggested as a possible explanation. At the lowest feeding rations, C. gracilis grown under silicate-limited conditions yielded the highest oyster growth rate of all three diets. When the growth responses of juvenile oysters fed various mixtures of the three C. gracilis cultures were examined, the highest oyster growth rates were obtained when 25% of the control algal cells was replaced with an equal number of nitrogen-limited cells. The results indicate that higher oyster growth rates are possible with additional carbohydrate, provided that adequate protein and essential fatty acids are supplied.

Review of the genetics and the potential for selective breeding of commercially important bivalves

Abstract The domestication of species used in aquaculture will not be complete until we have control over all aspects of their biology including their genetics. For virtually all shellfish, we are at present far from having that control but significant advances have been made in the past few years towards understanding many aspects of their genetics. In this paper will be presented a review of recent advances in, and an assessment of the state-of-the-art of shellfish breeding. Breeding here is meant to imply that we are concerned with the genetic control, manipulation and improvement of traits of commercial interest. The ultimate objective of the breeder is to produce strains which are genetically improved. There are several studies which give us an indication of the potential of such selective breeding both through heritability studies and experimental selections. These studies indicate that there is the expected potential and that what is needed next is a major commitment to develop selected lines. The various aspects of bivalve genetics such as Mendelian genetics, population genetics and quantitative genetics will be reviewed in the light of their roles in breeding for the improvement of the economic value of shellfish.

Response to within family selection for body weight in Nile tilapia (Oreochromis niloticus) using a single-trait animal model

Within-family selection for improved growth at 16-weeks was undertaken on Nile tilapia (Oreochromis niloticus) from 1986 to 1996. Data from 12 generations of selection were analyzed by a single trait Restricted Maximum Likelihood fitting an animal model. The heritability in the base population was estimated as 0.385. A genetic response for body weight was found with an expected mean increase in body weight per generation of 2.2 g or about 12.4%. A realized heritability estimate of 0.14 was obtained based on the regression of mean breeding values on cumulative selection differentials after 12 generations. The inbreeding coefficient was 6.3% after 12 generations with an average inbreeding of 0.525% per generation. The family rotational mating used to propagate the families was effective in keeping the inbreeding rate to a minimum even at high selection intensities. High selection intensities and the relatively high heritability for body weight at 16 weeks resulted in substantial response using the within-family selection method.

Selection for growth rate in the European oyster, Ostrea edulis: Response of second generation groups

Abstract A selective breeding program for increased growth rate in the European oyster, Ostrea edulis , produced second generation selected groups in 1979. The offspring were evaluated in 1981 for size and survival. Performance was compared to first and second generation unselected control groups. Although the selected offspring were on average consistantly heavier than the controls, the only statistically significant difference was in improved survival. The improvement in growth rate does not equal that of the first generation selected stocks. Evidence from the two types of controls suggests that inbreeding depression may be limiting the improvement through selection.

Genetics of shell color in Mytilus edulis L. and the association of growth rate with shell color

Abstract A number of crosses were made with individual mussels, Mytilus edulis L., which varied in shell color. The results confirm a previously published report that variation in shell color is predominately determined by a simple genetic mechanism. A study of several year classes from two separate populations shows that: (a) there is a substantial difference in the frequency of color morphs; and (b) within each population and each year class the brown morphs are 10–20% smaller than the blue morphs. These results have implications for the commercial culture of mussels.

Power from the people : a documentation of non-governmental organizations' experience in community-based coastal resource management in the Philippines

Community-based coastal resource management projects facilitated by non-governmental organizations (NGOs) in the Philippines have explored approaches to decrease poverty-driven over-exploitation of coastal resources. There has been little reporting and analysis of such activities until recently. Nine case studies have recently been published and this paper presents a brief summary of these, along with an analysis of the trends and themes identified. Though diverse and covering the Philippines from Mindanao to Luzon, the case studies highlight the value of community commitment and participation in decisions regarding, and in the implementation of, resource management in ways that consider not only the bio-physical aspects of resource management but the social, economic and legal implications. Experience in working with local government has been both successful and limited. Successful projects raise hopes for further progress through education and organization of communities to improve livelihoods and protect coastal resources.

Polyculture of scallopChlamys farreri and kelpLaminaria japonica in Sungo Bay

Several polyculture models of scallopChlamys farreri and kelpLaminaria japonica currently employed in Sungo Bay and other parts of northern China are described in this paper. Economic benefits of different polyculture models are analysed based on the growth rate, culture density and market price. In addition, site selection, critical environmental conditions and polyculture problems are discussed in detail.

Phenotypic analysis of the european oyster Ostrea edulis L.: Relationship between length of larval period and postsetting growth rate☆

Abstract Individually tagged oysters ( Ostrea edulis L.) from two year classes were monitored from day of setting to a mean size of 61 and 73 mm. The length of larval period (LLP) was measured as the numbered days from release to setting. In some spawning groups, the LLP was found to be negatively correlated with the size of individuals during the first season (mean size of 14 to 23 mm). However, in subsequent seasons, the correlations become close to zero and, at last measurement, the effect of LLP had disappeared completely. Although culling of slow-growing larvae will have no impact on improving growth to market size, it may be important in improving the economics of intensive nursery culture.

Genetics of growth rate in the American oyster: Absence of interactions among enzyme loci

Abstract Heterozygosity at seven enzyme loci explains about 4% of the variance in body weight (hence, growth rate) of 1-year-old American oysters ( Crassostrea virginica ). The various electrophoretically-detected loci affect body weight independently of each other, and there is not much gametic phase disequilibrium among loci in the natural population that was sampled. Thus, there is considerable evidence for overdominance (interaction of alleles at the same locus) but little evidence for epistasis (interaction of alleles at different loci). As a result, we predict a large dominance component in the variance of growth rates in natural populations, and expect that most of this component will be explainable by the one-locus effects. The independence of enzyme loci increases their value as markers in a selection programme. As more loci are examined, additional information is obtained about possible genome components affecting growth rate, which would not have been true if there had been strong epistatic interactions. This result is valid regardless of whether there is a cause-effect linkage or an associative linkage between the electrophoretic markers and the genes affecting growth rate. In principle, this search is limited only by the number of loci whose products can be detected by electrophoresis or other biochemical techniques, and by the number of loci which are polymorphic in the base population.