Impact of 17[alpha]-Ethynylestradiol Increase on Post-Spawning Mortality in the Female Siamese Fighting Fish

17[alpha]-Ethynylestradiol (EE2) is a synthetic hormone that has become a widespread problem in the aquatic environments. The immunomodulatory effects of EE2 in fish have attracted much attention in recent years; however, little is known about its immunotoxicological impacts. This study was conducted to investigate the immune function of female Siamese fighting fish exposed to an environmental concentration of EE2, 10 ng/L. Aggressive reproductive behavior in this species often results in injuries to females after spawning, and thus they are a good candidate in immunotoxic actions of EE2. Fish were exposed to EE2 for 15 days and then distributed for breeding. Immune function, pathogen resistance, and survival rate were assessed after spawning. Immune responses including serum concentrations of IgM, lysozyme, complement, and bactericidal activity were lower in EE2-exposed females than the control fish. Also, EE2-exposed females showed higher mortality rate regardless of whether they were challenged with the bacterium. These results suggest that EE2 suppressed immune responses of spawned female fighting fish, thereby reducing its potential to resist against opportunistic pathogens.