Bisphenol　A　(BPA)　is　a　well-known　endocrine　disrupting　chemical　(EDC),　ubiquitous　in　the　aquatic　environment,　which　poses　an　ecotoxicological　risk　to　the　health　of　aquatic　organisms.　However,　the　immunotoxic　effects　of　its　long-term　exposure　on　fish　have　received　limited　attention.　We　examined　a　number　of　typical　immune-related　parameters　and　oxidative　stress　indices　in　the　liver　and　blood　serum　of　the　red　common　carp　(Cyprinus　carpio),　following　a　30-day　exposure　to　five　different　concentrations　of　BPA　(0.1,　1,　10,　100,　and　1000　mu　g/L).　A　significant　increase　in　the　hepato　somatic　index　was　observed　in　fish　upon　exposure　to　1000　mu　g/L　BPA,　which　correlated　strongly　with　the　accumulated　BPA　concentrations　in　fish　bile.　Induced　oxidative　stress　was　also　apparent　in　the　exposed　fish　liver,　based　on　the　enhanced　levels　of　lipid　peroxidation　and　inhibited　activities　of　catalase,　superoxide　dismutase,　and　glutathione　peroxidase.　Serum　lysozyme　and　C-reaction　protein　levels　increased　at　low　concentrations　of　exposure;　however,　they　were　significantly　suppressed　upon　exposure　to　high　concentrations.　A　significant　increase　was　observed　in　the　levels　of　immunoglobulin　M,　complement　component　3,　and　alkaline　phosphatase,　in　both　fish　liver　and　serum　at　low　doses　of　0.1　and　1　mu　g/L.　This　suggests　that　long-term　exposure　to　environmentally　relevant　concentrations　of　BPA　(even　as　low　as　0.1　mu　g/L)　could　significantly　disturb　the　immune　response　of　fish.　Moreover,　RXR　alpha　expression　in　the　liver　was　significantly　altered　upon　BPA　exposure　and　the　trend　underlying　this　change　correlated　closely　with　those　of　the　most　immune-related　parameters,　implying　the　involvement　of　the　PPAR　gamma/RXR　alpha　signaling　pathway　in　regulating　the　immune　response　of　fish　upon　long-term　BPA　exposure.　In　short,　our　results　demonstrate　the　susceptibility　of　fish　immune　system　to　long-term　BPA　exposure.　Therefore,　the　immunotoxicity　of　EDCs　in　aquatic　organisms　should　not　have　been　underestimated.　(C)　2016　Elsevier　Inc.　All　rights　reserved.