Seahorses are protected by the Convention on International Trade in Endangered Species (Cites).
But they find ready markets in Vietnam and China, where they are ground up to make supposed aphrodisiacs.
In February 2015 French officials seized some 19,000 seahorses en route from Madagascar to Hong Kong.
Customs at Chilly-Mazarin, in the Paris region, said several parcels of dead seahorses had been intercepted in July and August. Sent from Conakry in Guinea, they had been stuffed into plastic bags and were bound for Hanoi.
French customs officials have seized about 2,000 dead seahorses - a protected species - in parcels from Guinea that were destined for Vietnam.