Beta-naphthoflavone-inducedCYP1A expression in the guppy Jenynsia multidentata: Time-dependent response, anesthetic MS-222 effect and fin analysis

• One hour exposure to BNF induces CYP1A transcription in fish organs and fin.
• A non-lethal assay with gonopodium evidenced CYP1A transcriptional induction to BNF.
• MS-222 influence on guppy CYP1A mRNA levels was evaluated.
• CYP1A mRNA levels were evaluated in South American guppy Jenynsia multidentata.

Cytochrome P450 1A (CYP1A) expression in fish is used as a biomarker of exposure to organic contaminants, such PAHs, PCBs and dioxins, in the aquatic environment. South American guppy fish Jenynsia multidentata were exposed to the prototypical aryl hydrocarbon receptor (AHR) agonist beta-naphthoflavone (BNF; 1 μM) and the fins were biopsied to characterize different aspects of CYP1A induction. RTq-PCR was used to quantify CYP1A mRNA levels in fish tissues. CYP1A induction in the gill, liver and anal fin (gonopodium) occurred within the first hour of waterborne exposure to BNF and persisted throughout 2, 4, 8, 24, 48 and 96 h compared to controls (DMSO vehicle; p<0.05). The organ-specific temporal pattern of induction was marked by mRNA levels consistently augment as duration of exposure increases and tend to a sustained induction from 24 h to 96 h for gill and liver (∼15-fold and ∼50-fold over control, respectively). In gonopodium, there was a maximum CYP1A mRNA level at 4 h (∼34-fold over control). Basal CYP1A mRNA levels and its induction following BNF exposure were not affected by administration of a chemical anesthetic (fish immersion in 100 mg l−1 MS-222 for 2–5 min) in the gill, liver, gonopodium, dorsal or tail fin (p<0.05). In an ex vivo assay, in which small pieces of biopsied fins were exposed to BNF for 4 h, high CYP1A induction was observed in the tail and gonopodium (∼49-fold and ∼69-fold, respectively) but not in the dorsal fin compared to controls. To our knowledge, this is the first study to show that a 1 h waterborne exposure to an AHR agonist is sufficient to cause CYP1A induction in fish organs and fins. The present study added new information to the field regarding the use of MS-222 as an anesthetic on fish and the analysis of biopsied fins as an alternative non-lethalex vivo assay for evaluating the CYP1A biomarker in fish. This observation could be useful for planning fish toxicological bioassays and biomonitoring studies on the aquatic environments in South America.