AQUATIC BIOLOGY Aquat Biol Vol. 18: 59–62, 2013 doi: 10.3354/ab00488 Published online February 14 INTRODUCTION The sea lamprey Petromyzon marinus L., 1758 is an anadromous species that, after several years in fresh- water habitats as larvae (Beamish & Potter 1975, Hardisty 1979, Quintella et al. 2003, Taverny et al. 2005), undergoes metamorphosis that allows young postmetamorphic lampreys to migrate to the sea and begin hematophagous feeding (Youson 1980). In the River Ulla (NW Spain), metamorphosis is completed between October and November, and downstream mi- gration occurs between October and May (Silva et al. 2013). After an unknown time at sea, individuals return to spawning areas in the river to reproduce. Upstream migration in the River Ulla occurs between December and May, and spawning occurs between May and July (Silva et al. 2013), which is similar to the timing of these events in Portuguese rivers (Quintella et al. 2004). At present, only the freshwater part of the biologi- cal cycle of the sea lamprey is partially known and, as is often the case with diadromous fish species, knowledge of biology and distribution during the marine portion of the life cycle is practically non- existent (OSPAR 2009). The overall picture of the distribution, growth and duration of the marine stage has been inferred from ca. 100 specimens from sporadic and isolated captures (Beamish 1980, Halliday 1991). Based on data obtained from these specimens, Beamish (1980) proposed a hematopha- gous feeding period of 2 to 2.5 yr, whereas Halliday (1991) suggested the possibility of a reduced feed- ing period (1.5 yr). Previously, using interspecific comparisons, Hardisty & Potter (1971) proposed that all the large anadromous lamprey species, including sea lamprey, have a hematophagous feeding period of at least 2.5 yr. © Inter-Research 2013 · www.int-res.com *Email: sergio.silva@usc.es NOTE Life cycle of the sea lamprey Petromyzon marinus : duration of and growth in the marine life stage Sergio Silva 1,2, * , María J. Servia 3 , Rufino Vieira-Lanero 2 , Sandra Barca 1,2 , Fernando Cobo 1,2 1 Universidad de Santiago de Compostela, Departamento de Zoología y Antropología Física, Campus Vida, 15782 Santiago de Compostela, Spain 2 Estación de Hidrobioloxía ‘Encoro do Con’, Castroagudín, 36617 Vilagarcía de Arousa, Pontevedra, Spain 3 Universidad de A Coruña, Departamento de Biología Animal, Biología Vegetal y Ecología, Facultad de Ciencias, Campus da Zapateira, 15008 A Coruña, Spain ABSTRACT: Little is known about the marine life-history phase of the anadromous sea lamprey Petromyzon marinus. The most widely accepted hypothesis suggests a hematophagous feeding phase of 2.5 yr. We captured and tagged (individually numbered T-bar anchor tags) 408 postmeta- morphic sea lampreys during the onset of the hematophagous feeding phase in the River Ulla and its estuary (NW Spain). One marked sea lamprey was recaptured during its spawning migration (total length: 895 mm, weight: 1218 g). This individual had been marked 13.5 mo before recapture, and had measured 218 mm and 20 g. Our results suggest that at least a portion of the sea lamprey population can reach adult size in 1 yr of hematophagous feeding. This further suggests a period between completion of metamorphosis and reproduction of 1.5 yr (18 to 20 mo). KEY WORDS: Growth · Adult · Feeding · Anadromous · Hematophagous · Estuary Resale or republication not permitted without written consent of the publisher