The general distributions of Petromyzon marinus, and Lampetra fluviatilis and L. planeri in Europe are similar and include much of the west and north, whereas Lethenteron japonicum occurs only in the north. The larvae of all four species occupy areas of shaded silt (optimum particle size: 180–380 µm) in parts of streams where current velocities are about 0.4 m/s. The gradients of streams in which they occur range from 1.9 to 5.7 m/km. Though differing in small details, the life cycles have much in common and spawning occurs usually in the spring or early summer. Both males and females spawn only once and die after reproduction. After hatching, the small larvae drift downstream to suitable silt beds. Larval life is variable and may last from 3 to 5 yr or even more. Larval metamorphosis and downstream migration occur during spring and summer and takes place mainly at night. The larvae of all species feed on fine particulate matter — mainly microorganisms and detritus. Adult L. planeri do not feed, but those of the three other species grow and mature in the sea where they are parasitic on a variety of marine and anadromous teleosts. There are considerable differences among the fecundities of the four species — related very much to the size of the adult females. Relatively few data are available on the population dynamics of any of the species. |
