Aquaculture: Broodstock Development and Genetics

The Broodstock Development and Genetics Group embraces a diversity of research projects on the population, evolutionary and aquacultural genetics of marine invertebrates. Principal activity funded by the California Sea Grant Program is devoted to controlling the reproductive cycle of lobsters so that a large scale selective breeding program can develop in step with the commercial cultivation of this species. A major breakthrough in this effort has been the discovery that ovarian development and egg extrusion are synchronized in groups of lobster females experiencing a transition from short day to long day photoperiods. Moreover, the conditions for and extent of mutual interference between growth and reproductive processes are now being documented. Since growth rate can be regulated by temperature and ovarian maturation by photoperiod, the implication of this research is clearly that it will be possible to control the entire life cycle of lobsters in captivity and manipulate reproductive cycles to yield seed for lobster farms on a year-round basis. Current research is aimed at better understanding the critical durations of certain photoperiod-temperature regimes needed to complete the lengthy reproductive cycle of Homarus. The European lobster (H. gammarus) frequently spawns annually in the laboratory, but most American lobsters (H. americanus) require about l8-20 months. Some exceptional annual spawnings by American lobsters have occurred, however, and we are hopeful of routinely shortening the cycle by photoperiod-temperature manipulation. In the meantime hybridizations between the European and American species of lobsters continue to bear fruit. We are anxious to test the fertility of the hybrids as the next step in assessing what intrinsic reproductive incompatibility, if any, separates the two described species of Homarus. Many of these Fl hybrids are approaching maturity, have received broodstock ID numbers, and several have been mated. One Fl female matured earlier this year, was mated to an Fl hybrid male and extruded a complement of F2 hybrid embryos. These eggs were unfortunately lost, a problem also encountered with other broodstock: research on the causes of egg loss, including the role of diet, has begun. Chemically mediated growth inhibition among juvenile lobsters has been discovered. An experiment has recently been completed on this growth inhibition as a function of flow rate through a linear array of compartments: the results should help discriminate between two alternatives, that the inhibitor is continuously produced or that it is intermittently secreted or excreted perhaps as a component of urine. Other studies on the species specifically of the inhibition and the role of body size differences are planned or in progress. An electrophoretic study of abalone was completed for Sea Grant to assess the extent of genetic differences among isolated populations in view of planned hatchery release programs. Several protein polymorphisms were found, but the frequencies of alleles did not differ dramatically among Channel Island and mainland localities. A three-year study of genetic divergence among oysters of the Crassostrea virginica group was initiated with NSF support. A field trip in Mexico last March allowed collection of live oysters from both the Gulf of Mexico and the Pacific coasts. Electrophoretic analyses are currently being made. A comprehensive review of all aspects of the genetics of crustaceans was completed for Academic Pressâ forthcoming Biology of the Crustacea, Vol. l. Student projects in this laboratory during the past year have included thesis research by Nicole Okazaki and Pat Gaffney, both of UCD, on the brine shrimp Artemia (funded by Jastro-Shields grants