New possibilities in triploid oyster farming

In Denmark, as in many other EU countries, the aquaculture sector has grown very slowly due to restrictions and red tape. This contrasts with the rest of the world where aquaculture is in healthy growth providing jobs and food security.

The sh farming sector in Denmark has been in steady decline, but farmed mussel production has increased from 1,000 tonnes in 2009 to 10,000 tonnes production in 2022.

e increase in mussel farming is due to a more positive regulatory framework where it was possible to get permits. e seaweed cultivation sector has seen much interest, but only nine tonnes have been harvested in total so far despite investments of more than EUR15m in di erent seaweed farming development projects. Now, interest is building in a novel species for Danmark—the triploid Paci c oyster (Crassostrea gigas). Due to the triploidy the farming of this alien species is risk free for the environment, where feral Paci c oysters are already abundant all over the country. It has taken more than 10 years to process the permit to farm triploid Paci c oysters, but now the Danish Environmental Protection Agency seems to be ready to issue permits for farming.

Pacific oyster is a high value species

e reason the triploid Paci c oyster is a potential candidate for aquaculture is that it commands a high price; the farmgate price for Paci c oysters in the EU is EUR4.7/kg (Eurostat) and the price for Paci c oysters imported to Denmark is EUR7.5/kg (Statistics Denmark). In contrast, mussels are EUR0.5/kg. In addition, the Paci c oyster is resistant to diseases like bonamia, a parasite that can cause lethal infections in shell sh, that has been wreaking havoc among companies trying to farm at oysters. Lastly, the growth is nothing less than spectacular—the market size of 100 g is reached within two summers, while the slower growing at oyster takes four years to reach same size.

In Denmark there are no tides. e traditional way to farm oysters in France and Ireland on tables in the tidal zone is not possible in Denmark. Instead, cultivation must be in oating bags that can be prone to storm damage, or lantern nets that need frequent pressure washing to keep them clean. e cost of labour in Denmark is very high making production that involves much manual work economically unviable. To cut costs, production using bottom-culture has been trialled with very encouraging results in selected areas in Denmark. is method removes the need for manual

The advantages of triploids

labour because it is possible to mechanise to a large degree the harvest and care of the oysters. ey oysters are re-laid in deep water at 10 g in spring and grow to 100 g by the autumn. e meat quality is decent and losses from predation by brown crabs and star sh are acceptable at 10-20.

Sector struggles with opposition from affected communities e authorisation system in Denmark for mussel and oyster farming has been put on hold for the last three years while the Fisheries Agency mulls how to deal with the tidal wave of NIMBYism that torments the regenerative aquaculture sector. How long it will actually take to process applications to farm triploid Paci c oysters, among other species, remains unknown.

Johan Wedel Nielsen Partner Aquamind +45

22 37 43 90

jn@aquamind.dk

Danish shellfish farmers can look forward to growing triploid Pacific oysters once applications to cultivate this species are approved.

Triploid oysters have three sets of chromosomes and are attractive for the commercial aquaculture industry because of their potential for fast growth, superior meat quality (also in the summer period), year-round harvestability, and low environmental pressure on wild populations due to their sterility.