The present work was carried out to study the gill histology and ultrastructure of the seabass, Dicentrarchus labrax; and to compare between these structures in fish specimens inhabiting waters with different salinities. Fish specimens of the sea bass (D. labrax) were collected from Gholion Pond at Kafr El-Shiekh Governorate (Salinity: 18-20 ‰); Timsah Lake at Ismailia Governorate (salinity: 35-37‰) and Bardawil Lagoon at Al-Arish, North Sinai Governorate (Salinity: 64 ‰).
Histological examination showed that the chloride cells in brackish waters are located within the epithelium of the inter-lamellar regions and secondary lamellae, but in marine and hypersaline waters they are located within the primary epithelium of the inter-lamellar regions. The flat elongated pavement cells of secondary lamellar epithelium in hypersaline specimens are more flattened than those in brackish and marine waters. The ultrastructure examination showed that chloride cells in specimens of brackish water are large; polygonal and ovoid in shape with a little population of mitochondria. While the chloride cells in specimens from marine and hypersaline waters displayed more rich populations of mitochondria. In marine and hypersaline specimens, each lamellar epithelium mostly consists of one layer of flat elongated pavement cell, while it consists of two layers in brackish water specimens.





Results of statistical analysis to gill characteristic counts and measurements of D. labrax inhabiting waters with different salinities revealed that there are statistically significant differences between groups for most counts and measurements as well as their ratios, except that of the pillar system diameter. Generally, most of the multiple comparisons (brackish versus marine; brackish versus hypersaline or marine versus hypersaline) are significantly varied