Effect of 17α-Ethinylestradiol on the Intestinal Calcium Carbonate Excretion Rate of Yellow Fin Sea Bream (Acanthopagrus latus)

Abstract

Marine fish maintain their hypotonic body fluids by drinking seawater, excreting excess salt, and retaining water. Calcium in seawater is precipitated as CaCO3 in marine fish gut to limit the Ca2+ availability for absorption from the ingested water to maintain Ca2+ homeostasis; this process is controlled by endocrine functions. This study was aimed to investigate the effect of the exposure to synthetic estrogen; ethinylestradiol (EE2), on the osmoregulation process (CaCO3 excretion rate from the intestine) and reproduction in the native fish species of Kuwait. The fish were exposed in a semi-static system to three treatments (control and 5 and 10 ng EE2/l of seawater) for two weeks, and then the terminal sampling was carried out. Blood samples were taken for vitellogenin (Vtg) analysis using Western blotting, dot blot, and immunohistochemistry (IHC). Calcium carbonate samples were analysed for the excretion rate and showed no significant difference in treatments indicating that no effect on osmoregulation was observed. Water samples were analyzed by the enzyme-linked immunosorbent assay (ELISA) for the concentration of EE2 in the exposure tanks, showing a 50% decrease in the nominal concentration after 24 h of exposure. Fish gonads and liver were dissected for histological examination, showing no obvious intersex in control and lowdose exposed group, whereas the high-dose exposed group showed signs of intersex. No Vtg was induced in the plasma and that could be due to many factors such as low concentrations received in the exposure tanks (2.3 and 4.9 ng/l), fish species, and exposure period. The hepatosomatic index showed no significant difference between treatments and the gonadosomatic index showed a significant difference between the control and high-dose group. Interesting results were obtained from IHC, where Vtg was localized in both treatments, although more Vtg was detected in higher-dose exposed fish for both tissues (liver and gonads).