Anatomy of finfish and shellfish

Unit 6 - Respiratory system in fishes

6.2.6. Lamellae (secondary lamellae)
The each gill filaments is made up of secondary lamellae which are actual seat of exchange of gases. They are generally semicircular and lined up along both sides of the gill filaments. The lamellae frequency is directly proportional to the dimension and resistance of the gill sieve. The secondary lamellae are having two sheets of epithelium which are separated by space and through these spaces blood circulates. The epithelial sheets are separated by a series of pillar cells. Each cell consists of a central body and is provided with extension at each end.