(1) Two individuals were kept in aquaria in order reathing movementa, behaviour to study their susceptibility to infection (2) One individual was decapitated and its head boiled in water for about 20 min. (3) Five individuals were cut immediately posterior to the pectoral fins and prepared as follows a) The covers were left (1 left cover was removed (2 individual e) The gill covers of both Rides were removed (2 fishes). All 5 were then carefully washed and fixed according to BourN (4) Four individuals were anaesthetized in MS 222 in the following ways a) MS 222 (cone. 1/3000); both gill covers were left intact (1 individual) b) MS 222 1/3000; both gill covers were removed. (1 individual) c) MS 222 1/1000; left gill cover was removed (1 individual) d) MS 222 1/1000; both gill covers were removed. (1 individual). Their heads were then cut off and fixed according to BouIN. Some fishes were roughly dissected under a pre- paring microscope in order to study the general anatomy of the pharynx Whitefish of groups 3 and 4 were carefully dissected under a preparation microscope by means of scalpels styles and tweezers. The 3 anterior gill arches were cut one by one, and a horizontal cut was made in the ventral part of the pharynx. The part of the roof of the pharynx and the anterior part of the oeso phagus were then carefully The dissec- tion was made in the dorso-posterior region of the gill chamber. Photos were taken after every cut. The 2 posterior gill arches were reconstructed by using a stick, paper and preparation microscope