Captive Care Notes: Northern Lampreys (Family Petromyzontidae)
If you want to observe lampreys close-up, ammocoetes and adults will live in the home aquarium. If caught at the right moment in their life cycle they will also spawn in captivity. However, the lamprey's secretive or parasitic tendencies prevent them from being more than just an aquarium novelty, better suited for study aquaria than the average commuity tank.
The best time to collect adult lampreys is during their spawning runs. Spawning lampreys have one thing on their mind -- sex -- and are oblivious to anything else. You should be able to scoop them up quite easily. Nonspawning adult lampreys can be collected as you would darters or sculpins, that is, by snorkeling with a handnet, or kick seining across the stream bottom. Ammocoetes, however, must be extracted from the river substrate. With a small plastic bucket, scoop up some mud or sand, dump it on the bank, then carefully finger through it looking for the wiggling larvae. Biologist Neal Mundahl reports good luck finding ammocoetes around submerged logs, where slow eddies apparently concentrate lamprey foods. Sifting through the muck with a dipnet also will occasionally produce ammocoetes, but they will usually slip through wider meshes before you realize what you have. If you live on the East or Gulf coasts, it's possible you will net some young American eels and mistake them for lampreys. Take along a filter box or some other clear container and fill it with river water to inspect what you catch. If you see a head with eyes and a mouth, then you're looking at an eel.
Ammocoetes are easy to keep in the home aquarium, but youšll seldom see them since they usually remain buried in the sand or gravel, feeding on microorganisms and particulate detritus. For this reason, make sure they are kept in a mature tank with a biologically active substrate, or with sand collected from their habitat. A recommended food for ammocoetes is moist Brewer's yeast, fed twice a week at a ratio of 105 grams per square meter of tank bottom. I've kept single ammocoetes in unfiltered 2.5-gallon aquariums containing a thin layer of sand. To check on them, I view the tank from underneath with a flashlight or hold it over my head under a light, whereupon I can see the lamprey larvae moving in the sand. Once I placed ammocoetes into a community tank with a gravel bottom. I never saw them until I broke the tank down, but the occasional sound of gravel being displaced assured me they were alive and well.
Biologists studying the metamorphosis of American Brook Lamprey (Lampetra appendix) maintained ammoceotes in a 77-gallon fiberglass tank with three inches of sand; lights were on 15 hours a day, water temperature seasonally fluctuated between 16-21C (61-70F), and the larvae were fed baker's yeast weekly at a rate of 1 gram per ammoceote per week. Metamorphosis began in easly July and immature adults began to appear in December.
Several biologists have kept and spawned various lamprey species in laboratory aquaria. The trick is collecting them at the right time. Aquarist and photographer John Brill (1985) published a superb account of his experiences with the Least Brook Lamprey for the NANFA publication American Currents. John placed two adult males and one adult female into a planted 10-gallon tank with coarse river gravel, undergravel filtration, and water temperature between 14.4-15.5C (58-60F). Within a day (and less than a week after capture) the males started fanning out a nest by attaching themselves to glass and thrashing their bodies about wildly. The female pitched in a day or two later. After three days John began to notice eggs (1 mm in diamater) in the nest. He also found the female's vent areas red and swollen, her mouth bloody, and presumably near death. John removed the adults (they would die shortly anyway) and left the eggs where they were. With the undergravel filter providing a beneficial flow of water across the eggs, they began to hatch eight days later. Opaque and white, the newly hatched larvae were boomerang-shaped and looked more like maggots than anything fishlike. None of them survived, however, perhaps because they were living in gravel rather than their preferred soft mud substrate.
If you wish to keep adult parasitic lampreys during their feeding period, then be prepared to feed them living, freshly dead, or thawed frozen fish. However, one aquarium publication reports that the Ohio Lamprey (Ichthyomyzon bdellium) usually accepts chunks of spinach and chopped beef heart. When it comes to fish, lampreys are not finicky, but one aquarium experiment with Silver Lamprey (I. unicuspis) showed they would rather just hang on carp and black crappie than eat them. In that same experiment the lampreys did 81.5% of their feeding at night. Captive Sea Lamprey, however, are more active during the day. Eventually, healthy parasitic lampreys will give in to their natural urges and start to fast in preparation for a spring spawning. Becker (Fishes of Wisconsin, 1983) reports that Silver Lamprey can fast up to six months in aquaria, during which they decrease 4-22% in length and 52-57% in weight.