Development and validation of an analytical method for the determination of 17β-estradiol residues in muscle of tambaqui (Colossoma macropomum Cuvier, 1818) by LC-MS/MS and its application in samples from a fish sexual reversion study

Tambaqui (Colossoma macropomum Cuvier, 1818) is the main native fish species farmed in Brazil, and 17β-estradiol (E₂) is a natural steroid hormone commonly used for the production of female fish monosex population, which, in tambaqui, shows a higher growth rate than the male. Thus, to assess whether the fish meat of treated tambaqui contains hormonal residue levels, a high-performance liquid chromatography coupled with electrospray tandem mass spectrometry (LC-MS/MS) method for the determination of E₂ residues in fish muscle was developed and validated. A QuEChERS (Quick, Easy, Cheap, Effective, Rugged and Safe) dispersive solid phase extraction method was used for the sample preparation. The chromatographic separation was performed in a Poroshel EC-18 reverse phase column. The mobile phase was a mixture of acetonitrile with 0.01% ammonium hydroxide (A) and water with 0.01% ammonium hydroxide (B). The ratio of A:B phases was 60:40 (v/v) used in an isocratic mode. The method validation was performed according to Commission Decision 2002/657/EC and Veterinary International Conference Harmonization (VICH GL49). Since matrix effects were observed, matrix-matched analytical curves are recommended for quantitation. The linearity, selectivity, intraday and interday precision, accuracy, decision limit, detection capability, and detection and quantitation limits of the method are reported. The limits of detection and quantitation were 0.3 ng/g and 1.0 ng/g, respectively. At these limits and slaughtering fish 7 months after the end of the treatment, the muscle of tambaqui did not show detectable hormone residue level. Thus, consumption of tambaqui edible tissue from fish treated with E₂ for the purpose of sexual reversion is unlikely to represent a risk associated with the exposure of human subjects as residue levels of this hormone are not detected in the fish muscle.

SHORT-COMMUNICATION Validation of reference genes for real-time quantitative PCR in tambaqui (Colossoma macropomum)

Tambaqui, Colossoma macropomum, is the main native freshwater fish in Brazilian aquaculture. Therefore, intensive research pressure has been applied to the species to support new technologies for tambaqui farming. Molecular biology represents a tool that can be used to investigate every field of applied biology, from fish physiology to the effects of climate change. Based on the importance of reference genes for the relative or absolute quantification of gene transcripts, we cloned and sequenced three candidate reference genes in tambaqui (18S ribossomal RNA - 18s, glyceraldehyde-3-phosphate dehydrogenase - gapdh, and actin beta - β-actin), and validated a set of primers for each gene for use in real-time quantitative PCR. The results were evaluated by RefFinder, which indicated that β-actin is the most suitable reference gene for tambaqui among those studied, followed by 18s.