EFFECTS OF TRIBUTYLTIN OXIDE ON SURVIVAL AND OSMOREGULATION OF THE SHRIMP PENAEUS-JAPONICUS (CRUSTACEA, DECAPODA)

The acute toxicity of tributyltin oxide (TBTO) was determined in larva e (nauplii, zoeae 1-3. mysis 1-3), post-larvae (PL stages) and juvenil e shrimp (Penaeus japonicus Bate), in two media, seawater (SW) and dil uted seawater (DSW; 1100 and 550 mosm kg(-1) approximate to 37 and 19% ). survival, osmoregulatory capacity and Na+-K+ ATPase activity were m easured. A gill and epipodite histopathological study was also conduct ed. The 24 and 48 h LC(50)s values for TBTO in SW ranged from 2.03 mu g 1(-1) (1.7-2.4) and 0.88 mu g 1(-1) (0.8-1.0) for nauplii to 773 mu g 1(-1) (344-1823) and 708 mu g 1(-1) (361-1608) for juveniles. The 96 h LC(50)s values in SW ranged from 19.4 mu g 1(-1) (12.6-27.3) for PL 5 to 370 mu g 1(-1) (202-662) for juveniles. The 96 h LC50 value was n ot affected by salinity in juveniles. Tolerance to TBTO tended therefo re to increase with the development from larval to juvenile instars. I n juveniles kept in SW and in DSW, acute TBTO-exposures decreased the osmoregulatory capacity (OC = difference between the hemolymph osmolal ity and the osmolality of the medium) of animals exposed to lethal and sublethal concentrations. Effects of TBTO exposure on hypo-and hyper- OC were time-and dose-dependent and the ability to osmoregulate was re covered after exposure of the shrimp to water free of TBTO for 48-120 h. These experiments confirmed OC as a valuable tool for monitoring th e physiological state of peneid shrimp. Gill and epipodite Na+-K+ ATPa se activities were not altered in SW and DSW after acute TBTO-exposure s, either at sublethal or at lethal concentrations. Haemocytic congest ion (thrombosis), multiple necrosis and nephrocyte hyperplasia were ob served in gill lamellae of exposed shrimp. Multiple necrosis and lacun ae in the epithelial monolayers were also observed in epipodites. At l ethal concentrations, the interconnecting lacunae were reduced and!or replaced by proliferating tissues. Epithelial cells were peeling and o edema was observed. For both tissues, histopathological effects increa sed with the dose and they are probably the cause of impaired osmoregu lation. (C) 1998 Elsevier Science B.V. All rights reserved.