Effect of an organophosphorus insecticide, fenitrothion, on survival, osmoregulation, and acetylcholinesterase activity in different life stages of two penaeid shrimps: Penaeus stylirostris and Penaeus vannamei (Crustacea, Decapoda)

The acute toxicity of fenitrothion was studied in seawater (36 PSU approxim ate to 1060 +/- 10 mosmkg(-1)) in larval, postlarval, and juvenile instars of the shrimp Penaeus stylirostris and Penaeus vannamei. The effects of thi s organophosphorus insecticide on juvenile hyper-osmoregulatory capacity (h ypo-OC), i.e., the difference between the osmolality of the haemolymph and that of seawater) and muscle acetylcholinesterase (AChE) activity were then recorded for both species at lethal and sublethal concentrations. In P. st ylirostris, 24 and 48 h LC(50)s for nauplii were above 500 mu gl(-1). The 2 4-h LC(50)s ranged from 160 mu gl(-1) (zoae 2) to 12 and 10 mu gl(-1) (mysi s 3 and postlarval instar 1) and from 11.2 mu gl(-1) (juveniles of 8 g) to 18.9 mu gl(-1) (juveniles of 20 g). The 48-h LC(50)s ranged from 42 mu gl(- 1) (zone 1) to 2 mu gl(-1) (mysis 3) and from 10.5 mu gl(-1) (juveniles of 8 g) to 16.3 mu gl(-1) (juveniles of 14 g). In P. vannamei, 24 and 48 h LC( 50)s for nauplii were above 500 mu gl(-1). The 14 h LC(50)s ranged from 324 mu gl(-1) (zoae 1) to 12 and 9 mu gl(-1) (mysis 3 and postlarval instar 1) and from 19.2 mu gl(-1) (juveniles of 7 g) to 41.5 mu gl(-1) (juveniles of 18 g). The 38 h LC(50)s ranged from 29 mu gl(-1) (zoae 2) to 10 and 8 mu g l(-1) (mysis 3 and postlarval instar 1) and from 19.2 mu gl(-1) (juveniles of 8 g) to 28.7 mu gl(-1) (juveniles of 12 g). Thus, for both species, tole rance to fenitrothion in seawater decreased with the larval development but increased with the weight of the juveniles. P. vannamei was more tolerant to fenitrothion than P. stylirostris, at most stages. In P. stylirostris, f enitrothion decreased hypo-OC and AChE activity. The decrease in hypo-OC wa s dose and time dependent. After 2 1 h of exposure at different sublethal f enitrothion concentrations, hypo-OC and AChE activity decreased significant ly by 5-22% and by 13-18%, respectively. In P. vannamei, hypo-OC and AChE a ctivity did not vary after exposure to sublethal concentrations. Only juven iles exposed to lethal concentrations and moribund shrimps showed significa nt AChE activity decreases. Hypo-OC and AChE activity appeared as good indi cators of physiological disturbance because of the pesticide in P. styliros tris but not in P. vannamei.