Sea Lamprey
There are many interesting anatomical features of sea lampreys.
They are eel like in shape, with 7 gill openings and an inconspicuous
median fin. This median fin becomes quite pronounced in the males as
they ascend the river in breeding condition. Though the lamprey's eyes
are small they are certainly functional. There is a third, pineal, eye
located on top of the head which functions to regulate circadian
rhythms. The entire skeleton is made of cartilage. The spinal cord is
supported by a notochord, rather than surrounded by a bony vertebral
column. Sexually mature adults average 2 to 2.5 feet in length..
The
anadromous life history strategy involves breeding in fresh waters and
migrating to the sea. At some point the seagoing adults return to the
natal streams to breed. Lamprey, like many anadromous
fishes, are
selmelparous, they come upstream once to spawn then they die. The
adults start moving up the river in late March and early April.