Effect of dietary Mirex and PCB's in combination with food deprivation and testosterone administration on thyroid activity and bioaccumulation of organochlorines in rainbow trout Salmo gairdneri Richardson

Abstract

Abstract. Serum thyroxine (T4) and triiodothyroninc (T3) levels were significantly lower in fish fed a high PCB diet (500 mg/kg) in comparison to those fed the control diet. The differences in serum thyroid hormone levels between the PCB‐fed group and those fed the control diet were not evident after 14 days food deprivation nor after testosterone‐injection. The low PCB diet (50 mg/kg) was without effect on serum T4 and T3 levels regardless of the treatment. Trout fed the highest Mirex diet (50 mg/kg) had T3 levels which were significantly lower and a T4 T3 ratio which T3was still evident after 14 days food deprivation but after testosterone administration the serum T3 levels in the control fish had fallen to levels similar to those in the Mirex‐fed group. The low Mires diet (5 mg/kg) was without effect on serum T4 and T3 levels regardless of treatment. Serum T4 and T3 levels in fish fed a mixed PCB (50 mg/kg) and Mirex (5 mg/kg) diet were not significantly different from controls but T3 levels were significantly higher than in control fish after 14 days food deprivation and subsequent testosterone administration. There were no appearence difference in anterior pituitary or thyroid histology between the different groups. The hepatosomatic index (HSI) in PCB‐fed trout was significantly larger than in controls in the fed groups, but not after 14 days food deprivation and subsequent testosterone administration. There was a five‐fold difference in carcass PCB hioaccumulation between fish fed the two PCB‐conlaminated diets, despite a 10‐fold difference in dietary levels of the organochlorine. Similarly despite 10‐fold differences in dietary Mirex levels in fish fed the 5 and 50 mg/kg and the 50 and 500 mg/kg diets, there were only 4–56–and 1–35‐fold increases in carcass Mirex content, respectively. Trout fed the mixed Mirex‐PCB diet had PCB levels of only 60.2% of those fed comparable levels of PCB alone (50 mg/kg) but contained similar levels of Mirex to those fed Mirex alone (a mg/kg).