Accumulation of waterborne iron and expression of ferritin and transferrin in early developmental stages of brown trout (Salmo trutta)

Abstract

Fertilized eggs, yolk-sac larvae and start-fed fry of brown trout (Salmo trutta) were exposed to various doses of waterborne iron. The iron levels of the intact eggs showed a dose-dependent increase following the treat-ment, while the levels of the embryos within the egg membranes did not differ significantly between the treated groups and the controls. After 4 days of exposure to ⁵⁹Fe, only 5% of the accumulated tracer was located in the embryos. Correspondingly, the iron content of the yolk-sac larvae was not significantly influenced by the ambient iron levels. In contrast, the start-fed fry appeared to be highly susceptible to waterborne iron. The accumulation of iron in the fry was suggested to increase with the development of the gills. The bioconcentration factor (the ratio of tissue-to-water concentrations of iron) declined with increasing iron exposure levels. mRNAs encoding the iron-binding proteins ferritin and transferrin were identified by reverse transcription polymerase chain reaction (RT-PCR) in the developing embryos 2 weeks after fertilization. Western blot analysis demonstrated the transferrin protein to be expressed in both the yolk-sac larvae and the start-fed fry, whereas no ferritin was detected in the early developmental stages of brown trout.