Question

Statement (S): Marine lampreys migrate to rivers for spawning.
Reason (R): Marine lampreys return to sea water after spawning.
A. Both S and R are correct but R is not the correct explanation to S
B. Both S and R are correct R is correct explanation to S
C. S is wrong but R is correct.
D. S is correct but R is wrong.

Answer 1

Hint: Migrations are a regular occurrence in many species of animals. Animals migrate for food, reproduction and many other reasons. Fishes migrate regularly. They swim across vast distances on either a daily basis or annually. They migrate to reproduce or in search of food.

Complete answer:
Marine lampreys, also known as sea lampreys, lamprey eels or lampreys belong to the species Petromyzon marinus Linn. They are scale-less and have an eel-like body. Their skeleton is made up of cartilage instead of bones. They possess seven functional gill openings behind their pair of eyes. Sea lampreys unlike other aquatic animals do not have a pair of fins rather they have single ventral and dorsal fin folds. They are distinguished based on the presence of suckers instead of a mouth. The sucker is a wide oral disc with sharp teeth arranged in consecutive circular rows. They use these suckers to latch onto their prey and feed off them. Adult sea lampreys can grow up to 47 inches and weigh around 2.5 kilograms. They are brown-yellow or olive in colour on their dorsal and lateral parts and have a lighter colour on their belly.

Sea lampreys are indigenous the Connective River Basin in the United States. They can also be found along the shores of Europe and North America in the northern and western Atlantic Ocean, the Black Sea, in the western Mediterranean Sea and the shores of the Great Lakes.

These species like any other aquatic species participate in migration. There are some particular types of migration. Anadromous migration in which fish migrate from sea to freshwater to spawn, and catadromous migration in which adult fish migrate from freshwaters to sea. Sea lampreys live in sea habitats and migrate to rivers for spawning. Therefore, they participate in anadromous migrations. Spawning refers to the process of depositing eggs and sperms into the water followed by external fertilization by aquatic animals and in this case the sea lampreys. The male sea lampreys dig up a nest with the help of a female sea lamprey. The female lampreys deposit its eggs in this nest. During spawning, the adults save up energy and halt other activities such as eating. The female lays eggs between 35,000 to 100,000. This is usually followed by the death of the adults due to the deterioration of their intestines. The larvae are blind and do not have teeth like the adult lampreys. They burrow in the sand and move towards downstream away from spawning areas. They feed on planktons and detritus and bear very little resemblance to adult lampreys. They transform into adults three to four years later.
In conclusion, sea lampreys do migrate up to rivers for spawning but they do not return to sea as they die after spawning. Their bodies provide food to smaller vertebrates and insects.
Therefore the statement is correct but the reason is wrong.

Hence, the correct answer is option (D).

Note: Lampreys are considered to be the Earth’s oldest inhabitants. Their fossils date back to 450 million years ago which is considered to be twice as old as dinosaurs!