borrowings outstanding (iii) a $0.4 increase in income incentive fee net of a one-time incentive fee waiver, (iv) a $0.2 million increase in the base management fee due to higher average total assets, and (v) a $0.2 million increase in professional fees.
Net investment income decreased by $(0.3) million, or (3.7)% to $9.3 million during the three months ended June 30, 2020 as compared to the same period in 2019, as a result of the $2.7 million increase in total expenses including incentive fee waiver and income tax provision, partially offset by the $2.4 million increase in total investment income. Adjusted net investment income(1), which excludes the capital gains incentive fee accrual, increased by $0.7 million, or 8.1%, to $9.0 million.
For the three months ended June 30, 2020, the total net realized gain on investments, net of income tax provision on realized gains, was $0.2 million, as compared to total net realized loss on investments, net of income tax provision on realized losses, of $(0.4) million for the same period in 2019.
Portfolio and Investment Activities
As of June 30, 2020, the fair value of our investment portfolio totaled $732.6 million and consisted of 64 active portfolio companies and three portfolio companies that have sold their underlying operations. Our total portfolio investments at fair value were approximately 98.2% of the related cost basis as of June 30, 2020. As of June 30, 2020, 20 portfolio company’s debt investments bore interest at a variable rate, which represented $210.3 million, or 32.0%, of our debt investment portfolio on a fair value basis, and the remainder of our debt investment portfolio was comprised of fixed rate investments. As of June 30, 2020, our average active portfolio company investment at amortized cost was $11.6 million, which excludes investments in the three portfolio companies that have sold their underlying operations. The weighted average yield on debt investments was 12.0% as of June 30, 2020. The weighted average yield was computed using the effective interest rates for debt investments at cost as of June 30, 2020, including the accretion of OID and loan origination fees, but excluding investments on non-accrual status, if any.
Second quarter 2020 investment activity included the following new portfolio company investments:
| • | | ECM Industries, LLC a global manufacturer and supplier of electrical products through a wide range of premium brands. Fidus invested $12.5 million in subordinated debt and common equity. |
| • | | Ipro Tech, LLC a provider of end-to-end eDiscovery and information governance software to top law firms, corporations, and specialty service providers. Fidus invested $2.5 million in first lien debt. |
As of June 30, 2020, we had debt investments in one portfolio company on non-accrual status and a debt investment in one portfolio company on PIK-only non-accrual status, which had an aggregate cost and fair value of $41.6 million and $21.4 million, respectively.
Liquidity and Capital Resources
As of June 30, 2020, we had $19.3 million in cash and cash equivalents and $57.0 million of unused capacity under our senior secured revolving credit facility (the “Credit Facility”). As of June 30, 2020, we had SBA debentures outstanding of $156.5 million, $50.0 million outstanding of our 5.875% notes due 2023 (the “2023 Notes”), $69.0 million outstanding of our 6.000% notes due 2024, $63.3 million outstanding of our 5.375% notes due 2024 (the “November 2024 Notes” and collectively with the 2023 Notes and February 2024 Notes, the “Public Notes”), and $43.0 million outstanding under our Credit Facility. As of June 30, 2020, the weighted average interest rate on total debt outstanding was 4.5%.