Breeding oysters is a core task at the new state-of-the-art hatchery at DTU Aqua in Nykøbing Mors. During spring, European flat oysters have been collected for breeding and for research. What does it take to breed oysters?
This spring, breeding oysters in the new hatchery at DTU Aqua in Nykøbing Mors serves a very specific purpose: Regenerating biogenic reefs - a task that is part of different marine restauration projects driven in collaboration with external partners.
During spring, Senior Researcher Camille Saurel and her crew have collected mother oysters in the Limfjorden that is right outside the hatchery, and lately the oyster larvae started to come alive – how is it going with these small creatures?
"To breed oyster, the most challenging part is the biosecurity and maintaining stable conditions in the hatchery including temperature, flow rate, feeding"
Camille Saurel, Senior Researcher, DTU Aqua
“We have had many swarming in the hatchery from the different broodstocks. The larvae have been kept in the larvae area and some have already been transferred for settlement,” says Camille Saurel.
Camille Saurel is in charge of the breeding in the hatchery and follows the development of larvae closely:
“When the larvae are released by the mother oyster, they are tiny and less than 200 µm length. Larvae take between 10-20 days before they are ready to settle and metamorphose to a pediveliger stage. At that point, they are bigger than 300 µm and have a black spot on their shell, black eye spot, and a small foot to settle.”
Spat-on-shell
“We place them in a settlement tank with micro-cultch which is crushed oyster shells, or larger substratum such as oyster shells to produce spat-on-shell that will be deployed in the wild for restoration-repopulation purpose.”
The process around breeding oysters – from collecting mother oysters over the spat-on-shell until some day they are suited for deploying at a seabed site to generate biogenic reefs – demands a keen eye on selection," Camille Saurel explains:
“In order to breed oysters and produce spat-on-shell, adult oysters are fished from the wild. At DTU Aqua, we select oysters that do not have Bonamia disease, hence all the fished oysters are screened for the disease.”
“Selected adults are then placed together in a breeding tank. We choose the number of tanks and number of breeding oysters taking into consideration their genetic diversity, to ensure that the released oyster population is genetically diverse.”
Ready for leaving home for their real home
“The larvae and spat produced are tracked, to follow the lineage of each batch which can be then monitored after restoration. Once the spats are bigger than 5mm they can be released in the wild and can leave our hatchery,” says Camille Saurel.
The art of breeding oysters relies on a steady and close attention. But, what is the most challenging thing about breeding oysters?
“To breed oyster, the most challenging part is the biosecurity and maintaining stable conditions in the hatchery including temperature, flow rate, feeding,” says Camille Saurel.
And what is the status of the European flat oyster in the Limfjorden in terms of Bonamia right now?
“The Limfjorden used to have a yearly monitoring for detecting Bonamiosis and Marteiliosis diseases. Marteilia sp. has never been detected in Danish water. The monitoring stopped in 2018, hence the current status of the flat oysters in Limfjorden in terms of Bonamia is not known.
DTU Aqua will over the next five year project period create biogenic reefs in the North Sea or Kattegat, and the breeding of horse mussels and flat oysters is the fundamental part of that work.
Photo: Tiny oyster larvae, by Camille Saurel