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Reproductive physiological characteristics of tropical Celebes eels Anguilla celebesensis in relation to downstream migration and ovarian development.

Downstream-migrating (n = 64) and non-migrating (n = 21) female Celebes eels Anguilla celebesensis were captured from the Poso Lake-River system on Sulawesi Island, Indonesia, and reproductive physiological characteristics were examined. In the histological observation of the ovaries, most non-migrating eels were at the perinucleolus (43%) or oil-droplet (48%) stage, while most migrating eels were at the early vitellogenic (36%) or midvitellogenic (61%) stage. Transcript levels of gonadotropin genes (fshb, lhb) in the pituitary and concentrations of sex steroids (11-KT, T, E2 ) in blood plasma of migrating eels were significantly higher than those of non-migrating eels. The fshb messenger (m)RNA levels were lower in perinucleolus and oil-droplet stages and then significantly increased in the early vitellogenic stage. The lhb mRNA levels in vitellogenic stage eels were significantly higher than those in perinucleolus and oil-droplet stage eels. The 11-KT levels during the oil-droplet and vitellogenic stages were significantly higher than eels at the perinucleolus stage. The E2 levels during the vitellogenic stages were significantly higher than those during the perinucleolus and oil-droplet stages. These dynamics of the reproductive hormones represented the physiological background of oogenesis in A. celebesensis that has remarkably well-developed oocytes just before downstream migration. This article is protected by copyright. All rights reserved.