LAGOS (Reuters) - Shares in Nigeria's Fidelity Bank shed 2.5 percent on Friday after the financial crimes agency said it had arrested the lender's chief executive as part of an investigation into transactions made in the run-up to elections last year. Nnamdi Okonkwo, Fidelity CEO has been in custody of the Economic and Financial Crimes Commission (EFCC) since Wednesday, the agency said on Thursday. Fidelity Bank said in a statement on Thursday that "the transactions were duly reported as required by the regulators" and it was cooperating with authorities. (Reporting by Oludare Mayowa; Editing by Mark Potter)