In vivoandin vitroeffects of mercuric chloride and sodium selenite on some non-specific immune responses of blue gourami,Trichogaster trichopterus(Pallus)

Thein vivoandin vitroeffects of mercuric chloride and sodium selenite on the non-specific immunity of blue gourami,Trichogaster trichopteruswere studied. Kidney lysozyme activity in fish treated with 0·09 ppm Hg2+for two weeks was significantly higher than the control, whereas the plasma lysozyme activity remained unchanged. In contrast, all SeO32−-treated fish showed no statistical difference in the kidney and plasma lysozyme activities after two weeks of exposure, except 0·5 ppm SeO32−-treated fish, which had a higher lysozyme activity in plasma. The zymosan-stimulated chemiluminescent (CL) response of head-kidney cells isolated from the naive fish was inhibited in the presence of Hg2+. This was decreased to about 50% and 10% of the control at 0·045 ppm and 0·09 ppm Hg2+respectively. On the other hand, the CL response of the head-kidney cells from the naive fish incubated with 4 ppm SeO32−was enhanced significantly. However, the CL response of the head-kidney cells isolated from the fish that were exposed to either Hg2+or SeO32−for 2 weeks showed no statistical difference to control. Thein vivoeffect of Hg2+and SeO32−on the natural bactericidal activity of plasma was tested by using a fish pathogen,Aeromonas hydrophila(strains L37 and PPD134/91). At 0·09 ppm Hg2+, the colony forming unit (cfu) counts of theA. hydrophilawere significantly lower than the control. For the 0·1 ppm SeO32−-treated fish, a higher cfu count was encountered for strain L37 but not for strain PPD134/91. On the contrary, 0·5 ppm SeO32−caused no change in the cfu count for strain L37 but decreased significantly the count in strain PPD134/91.