Effects of hypoxia on the reproductive endocrine axis of the pejerrey (Odontesthes bonariensis)

Abstract

Recently, hypoxicareas have been identified in water bodies of the Pampas region due to humanactivity. The objective of this work was to study the effect of lowconcentrations of dissolved oxygen (hypoxia) on the reproductive endocrine axisof a pampas fish (Odontesthes bonariensis). Groups of 8 males and 8females were subjected to severe hypoxia (2-3 mg l-1) and normoxia(7-9 mg l-1) in 3000 l tanks by duplicate during the reproductiveseason (spring). After 21 days, 4 males and 4 females from each tank weresacrificed, and blood was drawn to measure estradiol (E2) andtestosterone (T). The brain, pituitary gland and a portion of the gonads wereextracted and processed to measure the expression of: gnrh1, cyp19a1b,fshβ, lhβ, fshr, lhcgr and cyp19a1a. Fromthe second experimental week, no spawning was found in the hypoxic females,while at the end of the treatment period no male released sperm. Fish underhypoxic conditions showed signs of gonadal regression, reduction of GSI andplasma levels of sex steroids. Furthermore, the expression of gnrh1 inboth sexes, cyp19a1b and fshr in males and only fshβ and cyp19a1a in females decreased incomparison with control fish. After 40 days under normal conditions, signs ofreproductive recovery were observed in the treated fish. The results obtaineddemonstrated that hypoxia generated an inhibition of some components of the pejerrey´sreproductive endocrine axis, but the effect was reversible.