PETROMYZON (SEA LAMPREY)

Contents hide

1) Introduction

2) Classification of Petromyzon (Sea Lamprey)

3) Geographical distribution

4) Habit and habitat

5) Comments on Petromyzon

6) Ecological Importance

7) Conservation Status

8) Special features

9) Identification

Introduction

Petromyzon, commonly known as the sea lamprey, is a jawless fish belonging to the class Agnatha and family Petromyzontidae. It is one of the most primitive vertebrates, showcasing ancestral traits that provide significant insights into vertebrate evolution. Resembling an eel in appearance, Petromyzon lacks jaws, paired fins, and scales, features that distinguish it from more advanced fishes.

Sea lampreys are known for their parasitic lifestyle during the adult phase, where they attach to the bodies of fish using their sucker-like mouths, feeding on their blood and bodily fluids. Despite being parasitic, they play an essential role in aquatic ecosystems, contributing to nutrient cycling and acting as indicators of water quality.

Classification of Petromyzon (Sea Lamprey)

Phylum :- Chordata (Dorsal tubular nerve cord, notochord and gill-slits present.)
Group :- Acraniata (No head, cranium or brain)
Sub phylum :- Vertebrata (Vertebral column present.)
Division :- Agnatha (Jaws and paired appendages absen)
Class :- Cyclostomata (Mouth circular, suctorial, without jaws)
Order :- Petromyzontiformes (Mouth with funnel, without tentacles. Nasopharyngeal pouch blind. Gills 7 pairs, open independently to exterior. Branchial basket well developed)
Family :- Petromyzontidae
Genus :- Petromyzon

Geographical distribution

Petromyzon marinus is found in world-wide sea waters, coastal regions, streams and lakes of North America, Europe, West Africa, Australia, Chile, Japan, New Zealand, Tasmania.
Native to the Atlantic Ocean and its associated freshwater systems in Europe and North America.
Also found in the Great Lakes, where it is considered an invasive species.
Prefers temperate zones and migrates between marine and freshwater habitats

Habit and habitat

Petromyzon is found both in salt and fresh-water. They lead an ectoparasitic life on other fishes, attaching to the body of host by buccal funnel and secreting an anticoagulant for continuous flow of blood. They are also anadromous i.e., ascending river for spawning. Carnivorous and predators.

Habit:
- Anadromous: Spends its adult life in saltwater but migrates to freshwater rivers and streams to spawn.
- Parasitic during the adult phase, feeding on the blood of host fish.
Habitat:
- Found in marine and freshwater environments, including rivers, streams, and coastal waters.
- Prefers clean, oxygen-rich waters for spawning.

Comments on Petromyzon

Commonly called as sea lamprey
Body is eel-like, measuring about 90 cm, and differentiated into head, trunk and tail. First dorsal fin, second dorsal fin and caudal fin confluent.
Skin is without scales, slimy, green, brown and with strong metallic lusture.
Head contains mouth but no jaws. Mouth is surrounded by a large, ventral, suctorial funnel with numerous horny teeth. The ‘tongue’ is toothed and piston-like.
Dorsal nasal sac and mouth are unconnected. Paired eyes are present behind nasal-aperture.
Gill-slits are 7 pairs and branchial basket is well developed.
Sexes are separate. Female with large anal fin. Male with urinogenital or copulatory papilla. The development includes ammocoete larva which is very important phylogenetic ally as it is regarded a connecting link between Amphioxus and cyclostomes.

Ecological Importance

Nutrient Cycling: As detritus feeders during their larval phase, they help recycle organic material in freshwater ecosystems.
Food Web Contribution: Serve as prey for larger fish and aquatic predators, supporting biodiversity.
Indicator Species: Sensitive to water pollution and habitat changes, making them a valuable indicator of ecosystem health.
Economic Importance : (i) Lampreys have very little food value, (ii) They injure and destroy fishes by sucking blood and causing secondary infection, (iii) Larval lampreys are used as bait for sport fishing and commercial fishing.

Conservation Status

Native Populations: Generally stable but locally affected by habitat destruction, water pollution, and barriers to migration (like dams).
Invasive Populations (e.g., Great Lakes): Managed through control programs due to their negative impact on local fish populations.
Not globally threatened but requires habitat preservation in native ranges.

Special features

Lampreys are the lowest jawless vertebrates and their nearest allies are the ancient ostracoderms of Silurian and Devonian periods. There are no fossil representatives of this group to indicate their course of evolution.
Sucker-Like Mouth: Equipped with numerous teeth and a rasping tongue, enabling it to attach to host fish and feed.
Ancestral Characteristics: Lacks jaws, paired fins, and scales, resembling early vertebrate ancestors.
Larval Stage: Lives as filter-feeding larvae (ammocoetes) buried in sediment for several years before metamorphosis.
Reproductive Strategy: Dies after spawning, contributing nutrients to the ecosystem.
High Resilience: Adaptable to varying salinities due to its anadromous nature