Spawning season at KAC

KAC tanks

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.

Spawning Season at Gloucester Point

spawning_resized

Individual families are kept in their own mini-downwellers before moving out to the nursery when they reach 1-2mm.

Our spawning season at ABC gets off to a later start than for commercial hatcheries.  But when we do, the scope of work is intense for about three months, until the slate of crosses is complete for the year.  For a while, I used to think of the hatchery as the center of operations for our breeding work, as in, it defined us.  But that notion has changed.

The hatchery is only one of our tools in the breeding process.  Sure, the crosses start here, but really they only stick around for 5 weeks before they are out in the nursery and, then, only in the nursery for about the same amount of time before they are in the field.  Ten weeks out of about 90 (the total length of time from spawn to selection) for any given cohort (a cohort is a group of spawns that were done at the same time).  Of course, what defines a breeding program is the number spawns in a cohort as well as the number of cohorts overall.

For example, first up this season was the founding population of families for our new family breeding approach.  It consisted of making 130 families (a mating between one male and one female) about three weeks ago, and then a re-spawn to fill in the families that were going less well than we wanted – another 44 crosses.  In the end we ended up with 115 individual cultures that made it to setting.  Our first cohort, then, was 115 low salinity families.  These families will be deployed to two low salinity sites in the early Fall.

Next up, our line spawns.  We continue to produce our bread and butter lines – DBY, XB, Lola, and hANA – even while we are starting our new families.  For lines, a cohort will consist of three lines from each of our test sites, York, Lynnhaven, and Kinsale.  Three lines from York will be one cohort, three lines from Lynnhaven – another, etc.

Finally, while the larvae from the lines are still growing, we do the final set of high salinity families – another 130 or so of them.  At the peak of the season, we might have about 150 individual, albeit small scale, spawns running simultaneously.  During “drops” (water changes) 6 microscopes will be in use examining the larvae.

All these crosses make for a flurry of activity in the hatchery.  The starting date is dictated by the arrival of our OAT (Oyster Aquaculture Training program) participants in about mid-April so we have sufficient help for the glut of spawns.  The end date is dictated by the deterioration of water quality for growing larvae in mid-July.  Overall, about three months of hatchery activity determines the scope of work for field tests in the following year.

Next up – Spawning Season at KAC.