Bernheim’s streams are home to at least 23 species of fish, and spring is one of the best times to see many of them. One of the first signs of spring is the spawning season of the least brook lamprey (Lampetra aepyptera). It is not an eel, nor is it a parasitic lamprey. It is nonparasitic fish, meaning it doesn’t feed on animals unlike other species of lamprey. It only feeds in the larvae stage by filter feeding in ripples and gravel of creeks. Adult lampreys do not feed since they do not have functional intestines.
In spring, adults can been seen creating nests and spawning in creek ripples. The lamprey create nests by using their disc-shaped mouths to move pebbles to form shallow depressions in medium and small creeks. Once the nests are created, multiple lamprey will spawn within the depressions and deposit their sticky eggs in the nests on the gravel and sand. Spawning usually occurs when males attach to the back of the female’s head while she is attached to a rock and wraps his tail around her body. They shake vigorously for a few minutes to release their gametes and to partially burrow their eggs.
The larvae lamprey will remain in the nest for a month then move to slow moving water where they will burrow and start to feed. The larvae will feed for 3 to 7 years on microscopic plants and animals and detritus in these sandy areas before beginning metamorphosis in late summer through the fall preparing for adulthood. Adult lamprey will only live for four to six months, when they die after spawning. Spawning usually occurs in March and April when the water temperature is between 10 to 16⁰ C (about 50 – 60 f).
The least brook lamprey is the most common species of lamprey found in Kentucky and can be found in almost everything with major drainage. The best time to see them is during spawning season in March and April. They prefer clean, clear gravel riffles and runs of small to medium streams. They are considered secure in Kentucky and are a welcome sight here at Bernheim Forest.