en عمومى General پژوهشي Research <strong>Background: </strong>This study investigated the effects of estradiol on plasma calcium and prolactin cells of <em>Heteropneustes fossilis</em> kept in calcium-deficient and normal freshwater<em>. </em><br> <strong>Methods: </strong>Fish were deprived of food and divided into groups A-D. Group A and B were kept in artificial freshwater with normal electrolytes. Group C and D were maintained in calcium-deficient freshwater. Vehicle was administered to groups A and C. Groups B and D were injected with estradiol. Plasma calcium levels and prolactin cells were studied after 1, 3, 5, 10 and 15 days.<br> <strong>Results: </strong>Normal-calcium freshwater: In group A calcium levels remained unaffected. In group B, estradiol provoked hypercalcemia from day 3 to 10 although calcium decreased after day 15. Prolactin cells in group B became degranulated after 10day. Nuclear volume increased from day 10 onwards.<br> Calcium-deficient freshwater: Calcium levels in group C decreased from day 1 to 3 thereafter increased from day 5 to 15. Plasma calcium of group D increased from day 3 to 15. In group C prolactin cells exhibited hyperactivity on day 3 and degranulation on day 5. Nuclear volume increased from day 5 onwards. On day 10 and 15 certain cells became degenerated. In group D degranulation of prolactin cells began on day 3 which proceeded to complete degranulation on day 10. Nuclear volume increased from day 5 onwards.<br> <strong>Conclusions:</strong> Estradiol enhanced prolactin production and increased blood calcium in food-deprived fishes kept in calcium-deficient medium suggesting that calcium needed for elevation of blood calcium was derived from internal sources. Estradiol, Prolactin Cells, Plasma Calcium, Fish Calcium, Catfishes, Estradiol, Fishes, Prolactin 45 51 http://ijt.arakmu.ac.ir/browse.php?a_code=A-10-74-4&slc_lang=en&sid=1 Susmita Srivastav 10031947532846006485 10031947532846006485 No Department of Zoology, Shiv Harsh Kisan P. G. College, Basti-272001, India. Diwakar Mishra 10031947532846006486 10031947532846006486 No Department of Zoology, Government Girls’ P. G. College, Ghazipur-233001, India. Sunil Kumar Srivastav 10031947532846006487 10031947532846006487 No Department of Zoology, D. D. U. Gorakhpur University, Gorakhpur-273009, India. Nobuo Suzuki 10031947532846006488 10031947532846006488 No PhD. Noto Marine Laboratory, Institute of Nature and Environmental Technology, Kanazawa University, Ogi, Noto-cho, Ishikawa, Japan. Ajai Kumar Srivastav ajaiksrivastav@hotmail.com 10031947532846006489 10031947532846006489 Yes Department of Zoology, D. D. U. Gorakhpur University, Gorakhpur-273009, India.