Click on the timeline to see descriptions of each event.

Spawning

Background

Excellence in Unnatural Acts: The spawns were executed at VIMS’ Gloucester Point oyster hatchery in an “unnatural” fashion. In nature, oysters are broadcast spawners. This means the oysters release sperm and eggs into the water column upon environmental cues (changes in water temperature, tide, food availability), the eggs fertilize in the water column and further develop. The method of “unnatural” spawning used is called strip spawning. For this method, the oysters first need to be conditioned. This process lasts approximately six weeks and involves manipulating the water temperature in holding tanks to simulate seasonal change as well as intensely feeding at regular intervals. These are cues to the oyster to prepare gonad (sperm and or egg) resources. Once the gonad region is fully developed, the oysters are ready for spawning . Strip spawning consists of shucking the oysters, identifying the sex (by examining a sample of gonad region under a microscope), choosing one or more females with healthy looking eggs and one or more males with healthy, active sperm. The sperm and eggs are then stripped from the oyster, mixed in a beaker and monitored for egg fertilization.

Larval Development to shelled oysters: The fertilized eggs are placed in larvae tanks where they divide and mature into larvae. The larvae are fed algae and the developmental stages monitored by viewing animals under a microscope. The larvae swim freely for several weeks before they are ready to set permanently. To avoid oysters setting on the inside of the tanks, they are sieved onto a screen when in the final stage of development (just before setting called the eyed larvae stage). The eyed larvae are then treated with a chemical (epinephrine) that triggers the setting mechanism. At this point the larvae are no longer swimming and are moved to a post set system of downwellers in densities up to approximately 300,000 animals per downweller. It is in this system where the individual larvae begin to put on shell. The chemical setting produces fewer numbers of oyster clusters and more single oysters which is essential for aquaculture.

Compliance to the Permit

In compliance with one of the provisions for the VSC trial set by the Army Corps of Engineers Permit, the sperm from the tetraploid males was certified di-haploid and the larvae certified 100% triploid at 2 and 4 days and at eyed stage (using flow cytometry).

See initial ploidy data.