Biochemical Changes in Hybrid Catfish (Heterobranchus bidorsalis,♂ x Clarias gariepinus,♀) Treated with Nuracron

The effects of sublethal levels of nuracron,dimethylphosphate-3-hydroxy-N-methyl-cis-crotonamide(0,0.625× 10-6,1.25×10-6,2.5×10-6,5.0×10-6 and 10.0×10-6) on biochemical changes(aspartate transaminase,AST,E.C.2.6.1.1;alanine transaminase,ALT;2.6.2.2;alkaline phosphatase,ALP,EC 3.1.3.1) in the organs(kidney,liver,gill) and muscle tissues of hybrid catfi sh Heterobranchus bidorsalis,♂× Clarias gariepinus,♀ mean weight,(277.76±53.11) g SD;mean total length,(35.69±2.80) cm,SD] were studied after a 23 d exposure in a renewal bioassay under laboratory conditions.Generally,nuracron inhibited AST,ALT and ALP activities in all the exposure concentrations,with ALT activity being mostly affected.The most elicited enzyme was ALP in the kidney (4 052.67±1610.45) IU/L],followed by AST in the muscle (908.44±218.34) IU/L] and ALT in the liver (160.29±73.68) IU/L].The ALP activity was 30.24 and 6.53 times greater than that of ALT and AST.The highest inhibition for AST(43.65%),ALT(47.88%) and ALP(57.98%) occurred at 10×10-6,0.625×10-6 and 2.5×10-6,respectively.The activities of the enzymes in all the organs did not show any direct relationship with the exposure concentrations of the toxicant.ALT activity in the muscle generally suffered the most compared with the other enzymes.The activities of enzymes in the liver were generally inhibited,with elevation at 5.0×10-6 for all the enzymes.The lower concentrations of nuracron(0.625 ×10-6～2.5×10-6) caused elevation in the activities of ALP,but the reverse was the case with the higher concentrations;these of AST and ALT were haphazard.The relative activities of the various enzymes in the organs showed that the order for AST was livermusclekidneygill;that for ALT:liverkidney,musclegill and that for ALP:kidneygillliver and muscle.However,for AST and ALT the activities in the organs of the exposed fi sh peaked at 5.0×10-6 nuracron.The alteration in the activities of the enzymes indicated that the extract interfered with the Kreb's cycle intermediaries and the transamination process,and therefore could elicit negative consequences on the physiology of the fi sh,a non-target species in the aquatic environment.