Ultrastructure of the glandular epidermis on the fins of male estuarine triplefins Forsterygion nigripenne

Abstract

Male estuarine triplefins Forsterygion nigripenne develop enlarged fin tips during the breeding season. Using light microscopy and scanning and transmission electron microscopy the fins of males and females were compared. Tall columnar cells proliferated in the fin epidermis of males but were absent in females. The columnar cells were packed with proteinaceous granules that were bound by a double membrane. Three stages of development of columnar cells could be distinguished; the most mature expanded and ruptured to release its content. The function of the glandular epidermis is unknown but behavioural observations suggested that the secretion was applied to the egg mass and thus may protect it from infection.