Variable changes of environmental and climatic factors on some endocrine disrupting compounds affecting thyroid hormones in Nile Catfish (Clarias gariepinus)

Global climatic change is receiving a particular attention because it is thought to cause habitat destruction and may increase exposure of humans to extreme temperatures, polluted air and water, extreme weather events and endocrine disrupters (EDCs) as heavy metals. The aim of the present study is to give new insight on the effect of some environmental and climatic factors that may affect the level of some heavy metals in the aquatic system and also the possible impact effects of these EDCs on thyroid function in male and female catfish (Clarias gariepinus).The study was conducted on the River Nile around Banha city (Kalubia governorate) and Idku Lake (Beheira governorate). Fishing trips to the studied areas were carried out every three months over a period of one year from (summer 2014–spring 2015). Ten fish samples (from each sex) were collected each season from every fishing site. Five water samples from each locality were collected seasonally. The climatic changes in both sites were recorded and heavy metals [(Zn); (Cu) and (Pb)] were determined in water and muscle samples. Quantitative determination of serum thyroid stimulating hormone (TSH); Triiodothyronine (T3) and thyroxin (T4) as well as T4/T3 ratio was also determined. The climatic changes in both sites were significantly (P < 0.01) influenced by season and locality. The three heavy metals were significantly (P < 0.01) affected with season except Pb was not detected in water from the two sites. Muscle heavy metals of both sexes from the two sites were significantly affected by season and location. TSH concentrations were significantly differed in all seasons for both fish sexes collected from Banha but only differed at autumn and spring for those from Idku Lake. Both sexes of fish showed significant variations in (T4) concentrations with location all over the year except at spring for males and at winter for females. T3 levels in the same site indicated significant variations between the two sexes at summer, autumn, spring and winter, spring in fish collected from River Nile and Idku Lake, respectively. Male fish from River Nile recorded lower T4/T3 ratios than females all over the year. The same significant lower ratios was present also at winter in fish from Idku Lake, while at summer, autumn and spring male fish had higher ratio than females