Petromyzon marinus

Inquiries: contact Adam P. Summers at UMASS – Amherst, Department of Biology, Amherst, MA 01003.

There are three classes of vertebrates that are considered fishes: bony fishes, cartilaginous fishes and the jawless fishes. This last group, also called agnathans, has both marine and freshwater representatives. The most common and well understood agnathan is the sea lamprey. This species is parasitic as an adult. Mode of life of the adult lamprey is as follows: The round mouth sucker is applied to the skin of the prey, and the flesh is rasped off by the protrusible toothed "tongue." The catfish illustrated shows scars due to former attacks from lampreys.

In contrast, the larval lamprey feeds on detritus and benthic invertebrates.

The adults are often used as the fish dissection in comparative anatomy classes. 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 lamprey is one of several anadromous species of the Connecticut River. 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. Last year over 40 thousand adult lamprey were seen on their upstream migration as they were lifted past the Holyoke Dam.

Lamprey breed in the Connecticut River's tributaries in late May and early June. Spawning takes place in stretches of streams where the bottom is stony or pebbly. Working in pairs, a male and a female make depressions 2 to 3 feet in diameter and about 6 inches deep in the streambed by dragging away stones by means of their oral discs, leaving the stones in a pile downstream. Stones as large as a baseball may be moved. The female now secures herself by means of her oral disc to some large stone near the upstream end of the nest. Her mate attaches himself in the same way near her and wraps himself partly round her; then both stir up the sand with vigorous movements while eggs and milt are simultaneously deposited. Sand grains stick to the fertilized eggs and the larvae develop in the stream's sediments. After spawning the parents die. The larval or ammocoete stage lasts from 3 to 5 years, during which time the larvae live under stones or in the mud and subsist entirely on microscopic organisms filtered from the water. When the larvae reach 4 to 5 inches in length, they undergo transformation to the adult form and migrate downstream to the sea. (To see lamprey nests, visit the Fort River in Amherst, MA, under the bike path bridge in early June).

References:

Bigelow, H.B. and W.C. Schroeder. 1948. Cyclostomes In:

Vol 1, pp. 85-125. Academic Press, London.