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

Abstract

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 their reproductive physiological characteristics were examined. A histological observation of the ovaries revealed that most non‐migrating eels were at the perinucleolus (43%) or oil‐droplet (48%) stage, whereas most migrating eels were at the early vitellogenic (36%) or midvitellogenic (61%) stage. Transcript levels of gonadotropin genes ( fshb , lhb ) in the pituitary gland and concentrations of sex steroids [11‐ketotestosterone (11‐KT), testosterone, 17β‐oestradiol (E 2 )] 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 of eels at the oil‐droplet and vitellogenic stages were significantly higher than those of eels at the perinucleolus stage. The E 2 levels at the vitellogenic stage were significantly higher than those at 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.

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