The Nucleus Size and Possible Paedomorphosis of the Pituitary in the Goby, Rhinogobius flumineus

This study offers an example of the attempts to correlate the shape of an organ to the nucleus size. The pituitary glands of gobiid teleosts are partly embedded in the hypothalamus in contrast to those of non-gobiid teleosts. The pituitaries of the embryonic smelt, catfish, and guppy are partly embedded in the hypothalamus as in the embryonic and adult goby, Rhinogobius flumineus. The nucleus size of cerebellar granular cells, that may represent the genome size, is variable in gobies (16 species studied) as in non-gobiid perciforms (63 species studied). However, the ratio of the nucleus size of cerebellar Purkinje's cells to that of granular cells is consistently low in gobiids compared with non-gobiid perciforms. This ratio is a sort of peramorphic (morphologically advanced) index, and the low value may represent paedomorphosis (juvenile morphology). The gobiid pituitary gland partly embedded in the hypothalamus may be the result of paedomorphosis that could be reflected in the relatively poor increase rate in the size of Purkinje's cells as against the genome size.