Assessment of estrogenic and thyrogenic activities in fish feeds

Normal functioning of the endocrine system is essential for the proper development and reproduction of animals. Substances interfering with its homeostasis are called endocrine disruptors (EDs) and may represent a risk for the health of the organism. One of the mechanisms of endocrine disruption that has attracted great attention in recent years concerns alterations in the normal functioning of the estrogen receptor (ER), but far less attention has been paid to those substances interfering with the thyroid axis, which, in fish, plays several critical roles in a variety of biological functions. In aquaculture, feedstuffs can be a source of hormones or persistent pollutants which act as potential EDs. In this study, the main purpose was to assess the possible estrogenic and thyrogenic activities of 32 commercial fish feeds. For the assessment of estrogenicity, a new estrogen receptor specific reporter gene assay using sea bass ERα (sbER α) was developed and validated. Potential thyroidal disruption was screened with a cell line permanently transfected with luciferase as reporter gene under the control of avian thyroid receptor α (THRα). The results obtained showed that 11 and 18 out of 32 assayed feeds were able to activate the sbERα or the avTHRα1, respectively. The present study is pioneer in demonstrating thyrogenic activity in fish diets commercially available and widely used in aquaculture. Given that maintaining the homeostasis in the endocrine system is critical for the proper development and reproduction of fish, any estrogenic or thyrogenic activity caused by the feedstuffs should be taken into account with regards to its potential impact on farmed fish. ► Estrogenic and thyrogenic activities in fish feed extracts were assessed. ► A new stably transfected cell line with the sea bass estrogen receptor was used. ► Estrogenic activity was detected in 11 out of 32 tested pellets. ► A strong activation of the thyroid receptor was caused by 21 of the 32 tested feeds.