EFFECT OF AN ORGANOPHOSPHORUS INSECTICIDE, FENITROTHION, ON SURVIVAL AND OSMOREGULATION OF VARIOUS DEVELOPMENTAL STAGES OF THE SHRIMP PENAEUS-JAPONICUS (CRUSTACEA, DECAPODA)

The toxicity of fenitrothion was determined in larvae (nauplii, Zoeae 1 to 3, Mysis 1 to 3); postlarvae (PL stages) and juvenile shrimp (Pen aeus japonicus Bate), in two media, seawater (SW) and diluted seawater (DSW) (1100 and 550 mosMkg(-1),similar or equal to 37 and 19 parts pe r thousand S). The effects of fenitrothion on the osmoregulatory capac ities (OC) of juveniles were recorded. A gill and epipodite histopatho logical study was also conducted. For larvae in seawater, 24 and 48 h LC(50)s ranged from 32.9 mu g 1(-1) (Zoeae 2) to 10.7 mu g 1(-1) (Mysi s 3), and from 3.9 mu g 1(-1) (Zoeae 3) to 2.0 mu g 1(-1) (Mysis 3), r espectively; 48 and 96 h LC(50)s in postlarvae (PL) at the same salini ty ranged from 1.8 mu g 1(-1) (PL1) to 0.6 mu g 1(-1) (PL5), and from 0.3 mu g 1(-1) (PL7) to 0.4 mu g 1(-1) (PL15). In juveniles, 96 h LC(5 0)s were 0.8 mu g 1(-1) in seawater and 1.5 mu g 1(-1) in diluted seaw ater. From hatching to juvenile stages, the overall trend was a rapid decrease (from nauplii to PL5-PL7) followed by a slight increase (from PL7 to PL15 and juveniles) in the shrimp's ability to tolerate the in secticide. In juveniles kept in seawater and in diluted seawater, feni trothion decreased the osmoregulatory capacity (OC = difference betwee n the hemolymph osmotic pressure and the osmotic pressure of the mediu m) at both lethal and sublethal concentrations. This effect was time- and dose-dependent. In SW, the decrease in hypo-OC was similar to 25% at sublethal concentrations and similar to 35% at the 96 h LC50. In DS W, the decrease in hyper-OC was similar to 10 to 15% at sublethal conc entrations. In SW, shrimp were able to recover their OC in less than 4 8 h when transferred to water free of pesticide. In DSW, recovery at 4 8 h was only possible after exposure to the lowest tested sublethal co ncentration. Haemocytic congestions (thrombosis) of the gills, lamella e necrosis and other alterations of gills and epipodites (breakage of the cuticle, reduction of the hemolymph lacunae) were noted in juvenil es exposed to lethal and sublethal concentrations of fenitrothion.