LAMPREYS: CHARACTERISTICS, FEEDING, HABITAT, LIFE CYCLE - BIOLOGY - 2025

The lampreys or hiperoartios are jawless fish, ovoviviparous, marine or freshwater, classified in the group of agnates. Externally they are characterized by a smooth skin without scales, a disc-shaped sub-terminal mouth with multiple horny and pointed teeth, a pair of eyes, in addition to a pineal eye, two dorsal fins and a tail fin and a nostril orifice.

To breathe, it has seven pairs of gill openings, which are supported by an exclusive structure of this group called the gill basket. The branchial basket consists of an elaborate network of fused cartilaginous elements that supports the respiratory tracts and tissue.

Mouth of Petromyzon marinus (lamprey) in the Maremagnum Room of the Aquarium Finisterrae (Casa de los Peces), in La Coruña, Galicia, Spain. By Drow_male, from Wikimedia Commons

Biological and physical characteristics

Skeleton

The body of these animals is not supported by bone, instead they have a skeleton composed of mineralized cartilage, a material that provides them with a resistant, light and flexible support, relevant to their lifestyle.

The central axis of support in the body is the notochord, a solid cellular cord that supports the medulla and in more complex chordates it becomes the spinal column. This persists throughout the entire life cycle.

Mimers

Starting from the sides of the body, powerful muscular layers (myomers) extend, which are what provide movement to the animal. Encapsulated by the muscles are the organs, these are small and are attached to the body walls, with the exception of the ventricles of the heart and liver, which occupy almost the entire cavity.

Sense organs

They have a well-developed sense organ system. It consists essentially of compressed neuronal pillars, innervated by nerves and elongated support cells.

These neuronal pillars extend along the lateral line, around the mouth, eyes, and nostril, as well as between the branchial clefts.

The olfactory organ is distinguished by two things: its close relationship with the pituitary (being a receptor and encoder of hormonal messages) and its odd character, unlike the other groups of fish, which have paired nostrils.

Nose

The nostril in lampreys is located well back in the cephalic region, as an extensive chamber connected to the exterior through the nasal passage.

The olfactory chamber is lined by an epithelium consisting of long support cells, flattened olfactory cells, and a nerve connection to the olfactory nerve. Next to the eyes, the olfactory system allows lampreys to locate their food.

Feeding

Two feeding methods can be observed in lampreys: the first filter-type and the second as active predators.

Larvae

The life cycle of lampreys begins with a larva (larva ammocete). During this phase, lampreys live buried in the sediment, feeding on algae and detritus through a simple filtering mechanism.

Food is captured by hair cells, then enveloped by mucus and transported to the intestinal tract for digestion.

Adult

After metamorphosis and being adults, lampreys are either predatory or do not feed at all.

When they are predatory, lampreys are strongly attached to their prey, once located, they approach it and with the help of the tongue (provided with denticles) they begin to scrape the epithelium, creating a wound to which they attach and suck, taking just the flesh of the muscles and the blood.

Parasites

Once maturity is reached, some authors point to the group of lampreys as parasitic fish. However, unlike many species of parasites, they kill their prey as quickly as they can.

Taxonomy

Chordata

The taxonomy places this group within the phylum Chordata, which in turn are part of the superphylum Deuterostomia. These two large groups frame a complex of characteristics that are key in the early stages of development of living beings.

Craniata

In systematic order, the next classification is the subphylum Craniata. The subphylum is characterized because the organisms within this category protect the brain mass with a cartilaginous or classified chamber called the skull.

In the case of lampreys the protective chamber is called the neurocranium. This covers up to a third of the body surface of the animal. The neurocranium in lampreys is not fully fused, as is often the case in cartilaginous fish species. Instead, it is fragmented, providing flexibility.

In its posterior region, the neurocranium articulates with the notochord by means of pseudo-vertebrae. Laterally, the cranial base extends serving as support and protection for the auditory chamber.

Petromyzontomorphi-Petromyzontida-Petromyzontiformes

Within the subphylum Craniata is the super class Petromyzontomorphi, containing the class Petromyzontida and this in turn the order Petromyzontiformes.

About fifty species and eight genera of Petromyzontiformes (lampreys) have been described. As for these fish, there is a lot of controversy when defining the descriptive parameters that define lamprey species, for which the real number of species varies from author to author.

When the animals go through the metamorphosis phase from larva to adult, environmental conditions have a great influence on their final appearance, and the physical characteristics may be slightly modified in adults.

Changes in temperature or sudden concentration of some reactive component in the water are the main factors that favor the appearance of varieties and physical mutations in adult individuals.

Habitat and life cycle

Lampreys are anadromous organisms, a term that refers to the habit of certain marine creatures to migrate to fresh waters to reproduce and spawn, giving the larvae and juveniles the opportunity to grow in a more sheltered environment.

The reproductive event in these animals occurs once in their life, so once they have reached sexual maturity, adults begin a one-way trip from the marine environment to rivers and / or lakes.

The reproductive process involves laying the eggs (small, yellowish, 1mm in diameter, elliptical and with holoblastic segmentation) in a nest of circular shape and delimited by pebbles.

Upon emergence, the ammocete larva spends its entire life buried in the substrate, only poking its oral opening into the water column in search of food. There is a record that during this phase lampreys are exclusive to freshwater environments.

After approximately three years, the larva is completely buried in the substrate and the metamorphosis process begins, emerging after days or months (depending on the species), as a fully formed and functional adult, being able or not to feed..

If it happens that the species has the need to feed, it will immediately look for a host to adhere to and begin to gain energy to make the trip back to the sea. Once at sea they live associated with rocky bottoms and bento-pelagic fish. Once sexual maturity is reached, the cycle of return to the freshwater body begins.

Fishing history

1. De Luliis G, Pulerá D. 2007. The Dissection of Vertebrates, a laboratory manual. Elsevier. London England. 275 pp.
2. Ziswiler V. 1978. Special Zoology of Vertebrates. Volume I: Anamniotes. Editorial Omega. Barcelona, ​​Spain. 319 pp.
3. Alvarez J and Guerra C. 1971. Study of the growth in amocetos of Tetrapleurodon. Rev. Biol. Trop. 18 (1-2): 63-71.
4. Renaud C B. 2011. Lampreys of the world. An annotated and illustrated catalog of lamprey species known to date. FAO SPecies Catalog for Fishery Purpose, No. 5 Rome, Italy. 109 pp.
5. Nelson JS, Grande TC and Wilson MV H. 2016. Fishes of the World. Fifth Edition. John wiley & Sons, Inc. Hoboken, New Jersey, USA 707 pp.