On the Pituitary Remnant in “Cobalt” Variant of Rainbow Trout

Abstract

Histological investigations were made to clarify whether the pituitary gland was completely absent in the “cobalt” variant of rainbow trout and the following results were obtained: 1) The pituitary remnant adherent to the base of the brain was detected in three fishes among nine examined. The other six fishes were devoid of the remnant. 2) In all the fishes investigated, the detached pituitary remnant was found, located in the region ventral to the optic chiasma and dorsal to the upper pharynx. 3) The detached remnant was mostly composed of follicular cells. These follicular cells suggest the secretion of prolactin, because the cells are similar in their histological appearance to the prolactin cells of the normal pituitary gland in rainbow trout.