Comparison of the dietary organic and inorganic mercury threshold levels for the mercury toxicity in olive flounder, Paralichthys olivaceus

Abstract

This study was carried out to compare the dietary organic and inorganic mercury threshold levels for the mercury toxicity in juvenile olive flounder, Paralichthys olivaceus. Twenty-eight fish averaging 3.1 ± 0.05 g (mean ± SD) were randomly distributed into each of twenty-seven tanks. Each tank was randomly assigned to one of three replicates of nine experimental diets for eight weeks. The experimental diets were formulated to contain 0 (Control), 10 (IHg10, OHg10), 20 (IHg20, OHg20), 40 (IHg40, OHg40) and 160 (IHg160, OHg160) mg organic or inorganic Hg/kg diet. At the end of eight weeks of feeding trial, weight gain (WG) from fish fed control and 10 (IHg10, OHg10) diets were significantly higher than those from fish fed 20 (IHg20, OHg20), 40 (IHg40, OHg40) and 160 (IHg160, OHg160) (P < 0.05). Specific growth rate (SGR) and feed efficiency (FE) from fish fed control and 10 (IHg10, OHg10) were significantly higher than those from fish fed 40 (IHg40, OHg40) and 160 (IHg160, OHg160). Tissue mercury concentrations increased with dietary organic mercury content of diets. Mercury accumulated the most in kidney, followed by liver and gill. Broken-line regression analysis of WG indicated that the dietary Hg threshold toxicity level for juvenile olive flounder could be 13.5 mg Hg/kg diet in the form of HgCl2 and 8.7 mg Hg/kg diet in the form of MeHg.