Table 2 Freshwater fish studies on varied fish families, feeding types, number of the gill arches and gill raker, and the references supported that

Oreochromis niloticus

Cichlidae

Herbivorous

4

Semilunar in shape, the gaps between the gill arches were generally narrow. The gill rakers of the medial row were directed dorso-medially, while those of the lateral row were directed dorso-laterally. The gill rakers appeared as relatively short and wide-based processes with tuberous ends.

[29]

Chrysichthys auratus

Claroteidae

Omnivorous

4

The gill arch was semilunar in shape.

[29]

The gill rakers had two rows; the medial row was directed ventro-medially, while the lateral row was directed ventro-laterally. The gill rakers appeared as relatively short and broad-based processes with segmented tuberous ends.

Clarias gariepinus

Clariidae

Omnivorous

4 and additional 5th rudimentary

branched bulbous dendritic structures originating from the second and fourth-gill arches. The gill rakers were presented in three rows: medial, intermediate, and lateral. The medial and lateral row gill rakers were numerous with long processes, while those of the intermediate row were few and short. The medial row was found only in the third and fourth gills, while the intermediate row was found in the four main gills,

[29, 46]

Bagrus bayad

Bagridae family

Carnivore

4

Absent medial rows of gill rakers at the first and second gill arches, the number of gill rakers ranged from 14 to 16. The first gill arch carried well-developed long gill rackers, while the gill rackers on the following rows were short. Crescentic outlines with a wide interbranchial septum,

[3]

Nile tilapia

Cichlid

Changed to Omnivorous from herbivorous with an increase in size

4

The length of the gill rakers increased from the first to the fourth gill. The number of the gill rakers was variable in the different gills: they were 28 in the first gill, decreased to (25) in the second and third gills, but increased again to reach a maximum value (38) in the fourth gill.

[29, 46]

Tilapia Zilli, redbelly tilapia

Cichlid

Herbivorous

4

Each gill arch carried two rows of the small, short, wide-spaced gill rakers: lateral and medial. The gill rakers on each row were nearly the same in size, except the lateral gill rakers of the first-gill arch were longer. The gill rakers of the adjacent gill arches were interdigitated with each other. The lateral gill rakers on each gill arch were directed dorsolaterally, while the medial ones were directed dorsomedially.

[48]

Common carp (Cyprinus carpio)

Cyprinidae

Omnivorous

4

The medial edges of four gill arches with zippers have the potential to interlock. A significant reduction in gill arch length was observed from the first to the fourth, with the second and third gill arches having the greatest number of gill rakers (2nd (25.38 to 29.00) and 3rd (25.87 to 28.62). The length of gill raker increases from the first to the fourth gill arch.

[49]