Detailed measurements of gill area and constituent variables (total filament length, lamellar frequency and bilateral area) were performed on both hemibranchs of all eight arches in six specimens of gilthead sea bream Sparus aurata (mean ±s.e. 49·9 ± 0·2 g). Shrinkage was also quantified and results were corrected accordingly. Filament number decreased from the first to the fourth gill arch, and average bilateral area of secondary lamellae was higher in the second and third arches. Total and mean filament length, total number of secondary lamellae and total gill area (ATG) were lower in posterior than in anterior hemibranchs of the second, third and fourth gill arches; while the opposite was observed for the first arch. Lamellar frequency was increased in posterior hemibranchs of all arches compared to that in anterior hemibranchs, especially at the fourth arch. Comparison of the actually measured ATG and constituent variables with estimates revealed that the third gill arch is the most representative for appropriate measurements and that any of its components (even one hemibranch) approximates the best ATG (within the range of 0·2–4·3%, P > 0·05) and related dimensions. Consequently, necessary measurements were restricted to the posterior hemibranch of the third gill arch, and ATG and dimensions (y) were estimated in 21 specimens (23·5–217·6 g) and correlated to body mass (M) according to the allometric equation y = aMb. As fish increased in size, ATG (b= 0·664), total (b= 0·425) and mean (b= 0·323) filament length, total number of filaments (b= 0·103) and secondary lamellae (b= 0·377), as well as average lamellar bilateral area (b= 0·288), increased, while the opposite was observed for lamellar frequency (b=−0·049) and mass-specific area (b=−0·336). Data obtained are discussed in relation to S. aurata activity and living ethology.
Department of Applied Hydrobiology 2:
Department of Anatomy and Physiology of Farm Animals, Faculty of Animal Science, Agricultural University of Athens, Iera Odos 75, 118 55 Athens, Greece