Effects of Rhizopus extract administration on somatic growth and sexual maturation in lacustrine sockeye salmon Oncorhynchus nerka |
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| Authors: | RAMJI KUMAR BHANDARI IKUO USHIKOSHI HIDEO FUKUOKA NOBUHISA KOIDE KOHEI YAMAUCHI HIROSHI UEDA |
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| Institution: | ;Division of Marine Biosciences, Graduate School of Fisheries Science, Hokkaido University, Hakodate, Hokkaido 041-8611, ;Field Science Center for Northern Biosphere, Hokkaido University, Sapporo, Hokkaido 060-0809, ;Ushikoshi Research Institute, Sakura, Chiba 285-0813 and ;Azabu University, Sagamihara, Kanagawa 229-8501 and ;Hokkaido Fish Hatchery, Eniwa, Hokkaido 061-1433, Japan |
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| Abstract: | ABSTRACT: The filamentous fungi Rhizopus , like many fungal species, possesses physiologically active substances. Rhizopus extract (RU) is reported to be effective for various aspects of growth and reproduction in many vertebrates. The effects of RU administration on body growth and plasma levels of steroid hormones were investigated in lacustrine sockeye salmon Oncorhynchus nerka . One-year-old fish were fed daily with RU (20 mg/kg feed) from July 1999 to October 2000 for 15 months. Fish were sampled every month and plasma levels of testosterone (T), 11-ketotestosterone (11-KT), estradiol-17β (E2) and 17α,20β-dihydroxy-4-pregnen-3-one (DHP) were measured by time-resolved fluoroimmunoassay. Body growth of RU-fed fish of both sexes increased significantly in 1+ and 2+ October, and 2+ January–March and July. All RU-fed males and one female matured in 2+ October. RU-fed 1+ precociously mature males showed increased plasma levels of T, 11-KT and DHP in 1+ October. In 2+ males, RU significantly elevated plasma levels of T from May to June, 11-KT from June to July, and DHP in October. In sockeye salmon, administration of RU accelerated body growth of both sexes and sexual maturation in males, suggesting physiologically active substances present in RU enhance somatic growth and sexual maturation by sex-specific mechanisms. |
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| Keywords: | Rhizopus sexual maturation sockeye salmon somatic growth steroid hormones |
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