Effect of water-borne aluminum on serum parameters related to thyroid function of common carp (Cyprinus carpio)

There are many biotic and abiotic (such as toxic metals) factors that can affect different levels of thyroid system and consequently, alter normal function of body, including growth, osmoregulation and other physiological functions of organisms. In this study, following determination of LC50-96h of aluminum (Al3+) for common carp, 40 fish weighing 149.14±41.41 g were exposed to different levels of water-borne Al3+ (0.2804, 1.402 and 2.804 mg/l) and a group for control. At the end of experiment (30 days), 6 fish were sampled randomly from each treatment and blood samples were withdrawn from caudal peduncle region. Obtained results showed a significant decrease in T4 only following 2.804 mg/l Al3+ treatment in comparison with control (22.22%, P<0.05). Serum T3 level was reduced by 15.80 and 24.11% following treatment 2 and 3 respectively whilst serum TSH was elevated following treatments 2 and 3 by 73.18% and 3.08-fold as compared with control. Serum T3-uptake was unaffected following all Al treatments compared with control untreated group. Treatments 2 and 3 led to significant decreases in free thyroxine index (FTI) by 18.87 and 33.37% in comparison with control, respectively (P<0.05). Regarding to decreases in T3 and T4 as well as increases in TSH and FTI, it could be concluded that sub-lethal doses of Al3+ led toproduce hypothyroidism in common carp fish.