ABSTRACT
Th is chapter deals with the endocrine system of lungfi sh under the headings of pituitary, urophysis, hypothalamus and brain peptides, neuropeptides, thyroid, parathyroid, ultimobranchial gland + PTHrp, gonads and reproduction, ovaries, testes, kidneys and adrenal glands, the renin-angiotensin system, gastrointestinal tract and pancreas. Each of the features of the vertebrate endocrine system have been dealt with in turn for lungfi sh. Since only living lungfi sh are considered, the three genera – Neoceratodus, Protopterus and Lepidosiren are indicated for each new piece of information given. Th e resurgence in interest in lungfi sh endocrine glands and their hormones over the last 15-20 years has confi rmed their current phylogenetic position as sarcopterygian fi sh, more closely related to tetrapods than they are to other osteichthyans, particularly teleost fi sh. Interestingly, Neoceratodus, considered basal to the other two genera of lungfi sh, shows some similarities (e.g. morphology of pituitary, sequence of angiotensin II) with the basal actinopterygian fi sh such as sturgeon and paddlefi sh, while other hormone homology data, particularly for much larger peptide hormones, frequently fi nds closer similarity between lungfi sh and mammalian hormones than between lungfi sh and other tetrapods. However, the similarity between lungfi sh large peptide hormones and all tetrapod forms is always greater than between lungfi sh and teleost forms. Keywords: hypothalamus, pituitary, thyroid, adrenals, gonads
At the International Symposium for Comparative Endocrinologists held in Hong Kong in 1981, James Atz urged us to direct our attention to species of particular evolutionary signifi cance that have generally been neglected. Top of his list was the lungfi sh, Neoceratodus forsteri. I took up the challenge and at the following Symposium in 1985, I presented the fi rst account of steroid hormones during the reproductive cycle of Neoceratodus forsteri and thus had begun my ‘love aff air’ with lungfi sh which has involved collaborations with numerous other comparative endocrinologists over the intervening twenty years or so and will be the subject of this chapter. Neoceratodus has attracted morphological and anatomical study since its discovery in 1870 (Krefft ). Most of the endocrine studies to date have also been descriptions of the glands and more recently of the hormones, providing sequence data for many of them. Apart from the pioneering studies on osmoregulation by Pang et al. (1971) and Sawyer et al. (1976), there has been almost no experimental endocrinology on lungfi sh. Th is is not due to lack of interest but rather to their relative inaccessibility and to the diffi culties of keeping such large fi sh in captivity, while avoiding the confounding aff ects of stress. As my own interest in these amazing fi sh grew, I took on the challenge of setting up spawning ponds at Macquarie University in Sydney. Th e success of this venture has made some functional studies more possible. I will now discuss each of the major endocrine glands and summarise what is known to date about each in turn.
