Biochemical and histopathological endpoints of in vivo cadmium toxicity in Sparus aurata

Abstract

Cadmium (Cd) is a non-essential metal common in water bodies subjected to anthropogenic pollution. Its proven toxicity to aquatic and terrestrial organisms (including humans) has made this metal a subject of particular interest in toxicological studies, especially concerning common coastal fish species that are important marine resources, such as Sparus aurata. In order to establish laboratory tests and biomarker techniques to assess in vivo Cd toxicity in a multilevel (from histological to biochemical) approach, a short-term (48 h) assay was performed using juvenile S. aurata injected intraperitoneally with individual Cd dosages (0–8.1 µg Cd g^–1 fish w.w.). The results showed that Cd causes a fast and pronounced histopathological degeneration of liver tissue and an exponential induction in liver metallothionein-like proteins (MTs) strongly correlated to the injected Cd dosage (Spearman R = 0.97, P < 0.01) but not to Cd bioaccumulation or survival time. The relationships between Cd dosage, liver Cd, and liver MT suggested the existence of an absorbed Cd threshold after which the animals were no longer able to regulate and bioaccumulate the metal. This threshold was not dependent on survival time but rather on Cd dosage. The findings also confirmed the suitability of S. aurata as a test organism regarding toxicity caused by Cd. Complimentarily, a histological technique using a fluorochrome (acridine orange) to enhance tissue detail is described, as well as a method suitable for the detection of MTs in SDS-PAGE gels with a colloidal Coomassie blue stain.