The reproductive biology of Scleropages formosus (Müller & Schlegel)

The reproductive biology of Scleropages formosus (Müller & Schlegel) (Osteoglossomorpha, Osteoglossidae) in Malaya, and the morphology of its pituitary gland
D. B. C. Scott 1 J. D. Fuller 1
1 Department of Zoology, The University, St Andrews, Scotland
Copyright 1976 The Fisheries Society of the British Isles
ABSTRACT
This is a study of the reproductive biology and morphology of the pituitary gland of the osteoglossid fish Scleropages formosus (Müller & Schlegel). The fish spawn in the Tasek Bera waterways of Pahang, Malaysia during the rainy season beginning in August. Young fish are incubated in the mouth of the male parent until free-swimming. Males mature in their 2+ year, when 30–45 cm in length. In mature specimens the testis is small, and little sperm is produced. Some females mature in their 2+ year, although at that time, most have only reached the stage of secondary oocyte production. The chorion and follicular granulosa of secondary oocytes are deeply invaginated into the cytoplasm. All fish spawn in their 3+ year, when 45–60 cm in length. The single ripe ovary contains 20–30 ova, each 1.9 cm in diameter. No fish of 4+ years were caught, which may be the result of mortality or emigration, or due to extraneous causes such as selectivity in the fishing techniques used.

The pituitary gland accords with the generalized teleost pattern and embryonic development. There is no saccus vasculosus. Adrenocorticotropic cells predominate in the proadenohypophysis, and somatotropic and luteotropic cells occur here. The mesoadenohypophysis contains gonadotropic and somatotropic cells; the former grow large in ripe specimens, so that the mesoadenohypophysis becomes much enlarged. The metaadenohypophysis contains relatively few cells, much neurohypophyseal ramification, and is deeply penetrated by the third ventricle of the brain.