Morphological comparison of the detailed structure of gill rakers from three different feeding habits of marine fish species

Abstract

The feeding habits and habitat of different fish species influence the morphology and functions of their gill rakers. This study used gross anatomy and scanning electron microscopy to investigate the morphological features of the gill rakers in Siganus luridus, Boops boops, and Pagrus pagrus. The gill rakers appeared as medial and lateral rows in all studied fishes. Except for Pagrus pagrus, which had a unique gill rakers arrangement in which the medial row of the 4th gill arch had the most gill rakers, the longest and most gill rakers were on the 1st gill arch in all studied fishes. The gill rakers of Siganus luridus were smooth, with various spine-like shapes, such as spine-like gill rakers, which were bifid or trifid spines, or duck toe-shaped gill rakers. According to SEM of the Siganus luridus' gill rakers, the trifid end gill rakers resembled caterpillars, and the duck toe-like gill rakers had three or four finger-like spines connected by inter-spine tissue. The Boops boops had long conical gill rakers with pointed ends on the lateral sides of the 1st gill arch, and the remaining rows had short gill rakers. According to SEM of the Boops boops' gill rakers, the long gill rakers were semi-conical and only had needle-like spines on the medial surface. The short gill rakers were projected as a boat and had three different shapes based on spine distributions. Gill rakers include those with a median crest and long spine laterals, those with only lateral spines, those with usually dorsal spines, and those with long wedge-shaped spines. Pagrus pagrus’ gill rakers were short, with fine-needle spines covering their tops. By SEM of the Pagrus pagrus' gill rakers, they appeared as a cylindrical elevation with spines on top. The spines were conical in shape with pointed curved or straight ends. The maximum value of the gill rakers’ lengths was discovered in the lateral row of the 1st gill arch, while the minimum value was in the medial row of the 4th gill arch. As a result, this is the first study of the three fish species' gill rakers. In the studied fishes, the morphological characteristics of gill rakers demonstrated unique structural specifications in feeding behavior.