Tidal and circadian patterns of European eel during their spawning migration in the North Sea and the English Channel.

Technological advances in tracking methods enable the mapping of anguillid eel migration routes from continental habitats to their spawning sites in the ocean. However, the behaviour and orientation abilities of anguillids are still poorly understood, and have only rarely been studied on the continental shelf. Here we present the results of a study into the vertical and horizontal movement behaviour of 42 European eels (Anguilla anguilla L.) tagged with electronic tags that migrated through the North Sea and English Channel towards and into the Atlantic Ocean during their spawning migration. We used actograms, periodograms and linear mixed effects models to determine the periodicity and significance of the timing and pattern of vertical movement and activity. Overall, eels had a complex behavioural repertoire that included classical diel vertical migration (DVM), reverse DVM and vertical movement behaviours that synchronized with tidal patterns. All of the eels that were tracked showed one or more of these behaviours during their time at liberty, and many exhibited all of them. We also observed that the eels had a higher horizontal migration speed when the current in the favourable direction was stronger. This, together with the vertical movement synchronized with the tides, suggests the eels adopt selective tidal stream transport. Finally, tracked eels had a higher vertical movement range at night compared to daytime. We hypothesize that these behaviours are driven by bio-energetic efficient movement, navigation and predator avoidance.

Spinal cord compression secondary to extramedullary haematopoiesis in transformed polycythaemia rubra vera.

Polycythaemia vera (PV) is a clonal proliferative disorder of the bone marrow characterised by autonomous haematopoiesis, which results in a panmyelosis in the peripheral blood. It is typically characterised by an acquired mutation in JAK-2 V617F. Progression to myelofibrosis (MF), characterised by worsening cytopenias and the development of constitutional symptoms, is seen in up to 10% of cases. Extramedullary haematopoiesis (EMH) in the spleen is a common finding in myelofibrotic transformation, but elsewhere in the body it is extremely unusual. We report the case of a 69-year-old male whose PV progressed to secondary MF and who presented with compression of the thoracic spinal cord directly as a result of EMH. Cytogenetic and molecular findings in the bone marrow were in keeping with evolving myeloid disease. He was managed by surgical laminectomy with an excellent outcome. Extramedullary haematopoiesis may be seen in both PV and on transformation to MF. This very rare complication should be borne in mind when managing patients with myeloproliferative disorders.