Exe Shipping: All five 'Fluvius' ships appear in the Amasus online fleet and, I think, carry their logo.
FLUVIUS AXE/PLYM/OTTER are owned by one-ship UK companies and managed by Exe Shipping. Those three companies probably have Amasus investment as there is an Amasus appointed director, Arend-Jan Rozema
FLUVIUS TAMAR/TAW are owned by Quay Marine Services BV, apparently an Amasus subsidiary
However, the owners of Exe Shipping (Simon & Pauline Lyon-Smith and David Mason) also own Quay Marine Services Ltd - and David & Helen Mason own Quay Shipping Ltd. So I wouldn't be surprised if they are also involved in Quay Marine Services BV