Between 1706 and 1712, Klein travelled through England, the Holy Roman Empire, and the Dutch Republic in an educational journey, before returning to Königsberg.

Influenced by Johann Philipp Breyne, his works dealt with matters of zoological nomenclature, and he set up his own system of classification of animals, which was based on the number, shape, and position of the limbs.

Inspired by Johann Phillipp Breyne, Klein developed an interest in science as early as 1713 and began publishing in 1722.

The first part (1740), dedicated to the Royal Society, focused on understanding the auditory capacity of cartilaginous and spinose fishes.

Aristotle claimed, in his "History of Animals," that fishes possessed no evident auditory organs, but believed that nonetheless they must hear.

In section of the essay titled De Lapillis, eorumque Numero in Craniis Piscium (roughly translated as “The bones, their number in the skull of Fish”) Klein considers what parts of the head of fish serve as the organ of hearing, and by what passages the sensation of sound is communicated to them.

Klein also suggested that one could determine the age of fish by analysing the number and thickness of the Laminae and fibres of these bones.

[2] The name of the genus Kleinia was given to the plant family of Compositae (Asteraceae) by Linnaeus in honour of Klein's works.

[3] Although well respected by his colleagues,[2] Klein was nonetheless accused by some contemporaries of being unscientific, alleging that he based his beliefs on the hearsay and the claims of ‘credulous’ people.

Collinson accused Klein's assertion as being “contrary to nature and reason,” and provided observations of Marine officers, such as Sir Charles Wager, to further his claim.