Survival and Level of Thyroid Hormones and Ions in Armored Catfish (Loricariidae) at Increasing Water Salinity

— The paper presents the results of the study of survival, the concentrations of thyroid hormones and ions of armored catfish of the genus Pterygoplichthys at increasing salinity of water. A stepwise (every two days) increase in water salinity from 0 to 12.5‰ leads to a significant increase in the concentration of Na + , K + , Cl – , Ca 2+ ions in the blood of fish, but does not affect the level of thyroid hormones (free and total triiodothyronine, thyroxine) and the calculated ratio of these hormones. The data indicate a low involvement of the thyroid gland in the osmoregulation of armored catfish. It is confirmed that some specimens of armored catfish can tolerate water salinity up to 15‰ for 2 days. The possibility of dispersal of armored catfish along estuaries to neighboring river systems is discussed.