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On the structural peculiarities of the pituitary in some clupeoid fishes with a note on their probable evolutionary significance

1963; Wiley; Volume: 146; Issue: 2 Linguagem: Inglês

10.1002/ar.1091460204

1097-0185

A. G. Sathyanesan,

Fish Ecology and Management Studies

Abstract Hilsa ilisha has a well developed sella turcica comparable to that of Polypterus and Epiceratodus. The persistent orohypophyseal duct and parasphenoidal foramen of adult Hilsa ilisha may represent the retention of embryonic features such as those seen in Salmo trutta, Chanos chanos and Elops saurus. Since this duct is considered to be the persistent base of Rathke's pouch, its presence in adult Hilsa ilisha is an archaic feature which may be considered as the repetition of the condition observed in Polypterus , Calamoichthys and Latimeria. The presence of discontinuous orohyphyseal duct in the fry and fingerlings of Engraulis telara and Gadusia chapra suggests that it may be the remnant of an open buccal connection present during the embryonic condition. In all the specimens used in this study the hypophyseal cavity is in the form of a “tube system” restricted to the rostral pars distalis and it is formed by the constricted and separated portion of the diverticuli of the orohypophyseal canal. It is better developed in the adult Hilsa ilisha and Gadusia chapra than in Engraulis telara. This reduction in the prominence of the duct tends towards the reported condition in the “primitive teleosts” the trout and the eel. Though basically the pituitary of the clupeoid fishes described are of the typical teleostean type, the orohypophyseal duct and the hypophyseal cavity in the form of a “tube system” are distinctly chondrostean features. The presence of these features in different degrees of expression in these forms and the expression of ductile and tubular structure in the fry of Chanos chanos, Salmo trutta and Elops saurus together apparently provide a continuous range of variations from the typically chondrostean to that of the higher teleostean type where cavities and ducts are totally absent.