As I carefully wash a thousand larvae down into the corner of a mesh screen, sized to catch tetraploid eyed larvae, I think about how ridiculous this must look to anyone who has cultured larvae before. A thousand? Really? A thousand spills on the floor of a commercial hatchery when someone sneezes. Welcome to the game of tetraploids, where no number of larvae is too small.
The arena for the game of tetraploids is located in Topping at the Kauffman Aquaculture Center (KAC), conveniently down the road from Merroir at RRO, where, if the numbers of larvae get too small, I can drown my disappointment in Oyster Stout. The role of KAC in ABC operations has morphed considerably over the years, but has always been crucial. Built during the “era of ariakensis” exploration, it is no longer a quarantine facility per se. It really has two principle functions for us now: i)conditioning brood stock for spawning and then holding them back once ripe, and ii) the arena for the game of tetraploids – our hatchery away from the hatchery. As such, we operate it seasonally. The latter activity includes not only propagation of the next generation of tetraploids destined for industry distribution, but also R&D on tetraploids, including the generation of experimental families and, for the last two seasons, a site for experiments for NSF REU students working with me on tetraploid related issues.
For example, last year Joseph Matt looked into the fate of di-haploid sperm from mosaic tetraploid versus non-mosaic (i.e., “pure” tetraploids). This is a timely question insofar as the majority of tetraploids used for making triploids are mosaics (a combination of triploid and tetraploid cells). (It seems to be a feature in C. virginica tetraploids.) We found no differences in early larvae attributable to mosaics. This year, Brittany Peachey will look into more effective ways of making tetraploids from triploids using an alternative means of induction.
The game of tetraploids is one of those long duration games requiring patience. To get to the tetraploid state, you must first pass from diploid to triploid, and then from triploid to tetraploid. The latter step is not fun, requiring one to find triploid females that can be used in the very special cross that obtains to tetraploidy. In this step, I have carefully coaxed as few as a couple of dozen larvae into the corner of a screen for setting.
The good news (sort of) is that once you have your first generation of tetraploids, you can cross them to each other – 4n x 4n à 4n. The bad news (sort of) is that even this cross has “issues.” Once in a while, a 4n x 4n cross will be really good, which means average for any other kind of larval culture. But most of the time, the loss of larvae leaves you with a few thousand that reach setting size. Average hatching rate for a 4n x 4n cross, for example, is less than 20%. The one I did today was 6%.
KAC is an excellent place to do this work, however, partly because it is a hatchery away from the cacophony of the Gloucester Point hatchery, partly because it has a modicum of air conditioning (something absent at Gloucester Point), and partly because I get to choose the music – literally and figuratively. I guess you could say it’s my hobby hatchery – the oyster equivalent of a busman’s holiday.