title: Sexual characteristics of high-temperature sterilized male Mozambique tilapia, Oreochromis mossambicus.
abstract: BACKGROUND
  In order to clarify the effect of extremely high temperature on gonads of fish, juveniles of the Mozambique tilapia, Oreochromis mossambicus, at three days after hatching (d.a.h.) were reared at a high temperature (37 ± 0.5 °C) for 50 days. The heat-treated fish were then cultivated at a normal water temperature for over six months.
  
  
  RESULTS
  The testes of all individuals heat-treated for 50 days were sterile. Histological analysis revealed the complete absence of all stages of spermatogenic germ cells in the testes of the heat-treated males; however, structures within a layer of epithelial cells lining the efferent ducts were observed to actively secrete sperm fluid into the ducts, as in the mature testes of normal males. Clusters of cells immunopositive against P450scc and 3β-hydroxysteroid dehydrogenase were observed in the sterilized testes. Leydig cells had developed smooth endoplasmic reticulum and several mitochondria with tubular cristae indicating active steroidogenesis. The sterilized males displayed male nuptial coloration, actively dug spawning nests, and mated with normal mature females. However, females mated with these males initially brooded their eggs normally but released them prematurely at 4-5 days. All the released eggs were unfertilized and dead.
  
  
  CONCLUSIONS
  Heat-sterilized male tilapia matures endocrinologically but completely lacks spermatogenic germ cells.
authors.affiliation: Okinawa Churashima Foundation, 888 Ishikawa, Motobu, Okinawa 905-0206 Japan ; University of the Ryukyus, Sesoko station, 3422 Sesoko, Motobu, Okinawa 905-0227 Japan.
authors.forename: Masaru
authors.initials: M
authors.lastname: Nakamura
authors.affiliation: Okinawa Churashima Foundation, 888 Ishikawa, Motobu, Okinawa 905-0206 Japan.
authors.forename: Ryo
authors.initials: R
authors.lastname: Nozu
authors.affiliation: Hokkido University, Faculty of Fisheries, Graduate School of Fisheries Sciences, Laboratory of Aquaculture Biology, Minato-cho 3-1-1, Hakodate, Hokkaido 014-8611 Japan.
authors.forename: Shigeho
authors.initials: S
authors.lastname: Ijiri
authors.affiliation: University of Shizuoka, Laboratory of Molecular Reproductive Biology, Institute for Environmental Sciences, 52-1 Yada, Suruga-ku, Shizuoka 422-8526 Japan.
authors.forename: Tohru
authors.initials: T
authors.lastname: Kobayashi
authors.affiliation: Department Life and Health Science/Biotechnology Research, Teikyo University Science &Technology, Center2525 Yatsusawa, Uenohara, Yamanashi 409-0193 Japan.
authors.forename: Toshiaki
authors.initials: T
authors.lastname: Hirai
authors.affiliation: University of Hawaii, Hawaii Institute of Marin Biology, 46-007 Lilipuna Rd, Kaneohe, HI 96744 USA.
authors.forename: Yoko
authors.initials: Y
authors.lastname: Yamaguchi
authors.affiliation: University of Hawaii, Hawaii Institute of Marin Biology, 46-007 Lilipuna Rd, Kaneohe, HI 96744 USA.
authors.forename: Andre
authors.initials: A
authors.lastname: Seale
authors.affiliation: University of Hawaii, Hawaii Institute of Marin Biology, 46-007 Lilipuna Rd, Kaneohe, HI 96744 USA.
authors.forename: Darren T
authors.initials: DT
authors.lastname: Lerner
authors.affiliation: University of Hawaii, Hawaii Institute of Marin Biology, 46-007 Lilipuna Rd, Kaneohe, HI 96744 USA.
authors.forename: Gordon E
authors.initials: GE
authors.lastname: Grau
keywords: 11-ketotestosterone; Germ cell; High-temperature; Leydig cell; Male; Sperm fluid; Sterilization; Testis; Testosterone; Tilapia