Steroid hormone enrichment of Artemia nauplii

Abstract

Steroid treatment of fish species prior to sexual differentiation changes the developing gonad. Administration of steroids via the diet produces a higher percentage of sexually inverted individuals than other methods. However, hormone-enriched commercial diets are unsuitable for larvae of fish species, such as yellow perch, that require live diets (such as Artemia) during the time of sexual differentiation. Steroids have been added to Artemia at the first feeding instar II stage of development, but larger size would lend them unsuitable for larval fish requiring small zooplankton as their initial diet. To determine the effect of incubation with steroids prior to the first feeding instar II stage of development, decapsulated Artemia cysts were incubated in hatching medium with either 20 mg 17β-estradiol (E 2) or 17 α-methyldihydrotestosterone (MDHT) dissolved in 3 ml 70% ethyl alcohol or ethyl alcohol alone (control). Cysts were cultivated at 18–20°C for 24 h. Nauplii were collected by filtering culture medium, and were rinsed in 1 l of tap water. Artemia cultivated in control medium contained 0.07±0.01 ng E 2/mg dry weight, and E 2-treated Artemia contained 461±40 ng E 2/mg dry weight ( p<0.0001). MDHT-treated Artemia contained 546±31 pg/mg dry weight, and controls were below the level of detection (4 pg/assay tube; p<0.0001). Thus, steroid hormones were incorporated into Artemia prior to the first feeding instar II stage. Enrichment of Artemia at this smaller size will allow them to be used as the initial diet to cause functional sexual inversion of fish species that require small zooplankton.