TWO METHODS FOR DETERMINING THE FERTILITY STATUS OF EARLY-STAGE AMERICAN LOBSTER, HOMARUS AMERICANUS, EGGS

The American lobster (Homarus americanus Milne Edwards, 1837) is the focus of the most important commercial fishery in New England, which relies on a variety of biological monitoring programs and surveys to guide the development of appropriate management plans. One key piece of information provided by these surveys is the number of females that are carrying eggs (ovigerous) that will subsequently contribute new recruits to the fishery. A major assumption is that all eggs carried by ovigerous females are fertilized and will thus result in viable recruits. However, because some lobsters extrude, and briefly carry, unfertilized eggs, this assumption needs to be re-evaluated. In particular, it is important to determine the approximate proportion of newly extruded eggs that are either fertilized, or not. The major goal of this project was to develop reliable methods for determining if early-stage lobster eggs (live and preserved) were in fact fertilized. One method involved using a nucleic acid stain to visualize egg DNA, after pretreatment of eggs with a proteolytic and collagenolytic enzyme solution to facilitate stain penetration through the egg membrane. With this method multi-nucleated (fertilized) eggs could be clearly distinguished from unfertilized eggs. A total of 20 egg clutches were tested to determine their fertility status using this method. Of these, 16 clutches (80%) were fertilized while 4 were not fertilized (20%). Of the 16 clutches with fertilized eggs, two had a mix of both fertilized and unfertilized eggs. A second method, using fluorometry to obtain measurements of total egg DNA, was also developed. There was a significant difference between the total DNA concentration in unfertilized control oocytes and early-stage fertilized eggs (P < 0.001), and the total amount of DNA gradually increased as eggs developed (r = 0.961, P < 0.0001). Both of these methods will make it possible to make a more accurate assessment of the proportion of female lobsters that will actually contribute new recruits to the fishery.