American Savings Bank showed strong loan growth in the fourth quarter, but net income fell 15.2 percent primarily due to lower gains on residential mortgage sales and less fee income the bank collected from debit card transactions.

The state’s third-largest bank said Thursday it had earnings of $12.2 million compared with $14.4 million in the year-earlier quarter.

American Savings’ noninterest income, which includes residential mortgage sales as well as the card fees, fell 32.1 percent in the fourth quarter to $15.5 million from $22.9 million in the year-earlier period. A slowdown in refinancing reduced mortgage income while the bank also was affected by the Durbin Amendment, a federal law that puts a cap on the swipe fees that banks charge to merchants every time a customer pays with a debit card.

The bank, which during the second quarter earned an average of 49 cents per electronic debit transaction, now is getting only 21 to 24 cents per transaction under the recent law, which was designed to lower costs for merchants and, subsequently, customers. It went into effect July 1 for American Savings, a subsidiary of Hawaiian Electric Industries Inc., and the bank took in $1.5 million less after taxes from those fees in the fourth quarter than it did in the year-earlier quarter.

Hawaii’s improving economy, though, lit a fire under American Savings’ lending portfolio. Loans and leases ended the quarter at $4.2 billion, up 9.7 percent from $3.8 billion in the year-earlier period.

“We feel good,” said Richard Wacker, president and chief executive officer of American Savings. “We think the fourth quarter really capped a good year because we did get the good loan growth and at the same time saw improvement in credit quality and a lower provision for (loan) losses.”

The bank set aside just $554,000 during the quarter for potential loan losses compared with $3.4 million in the year-earlier quarter.

Wacker said the bank’s lending portfolio is benefiting from home equity lines of credit as well as from commercial real estate loans for new developments and commercial and industrial loans for businesses looking to expand their facilities.

The bank’s net interest income, the spread between lending rates and deposit rates, rose 1.4 percent in the quarter to $44.1 million from $43.5 million a year ago. Net interest margin declined to 3.67 percent from 3.81 percent.

Total assets rose 4 percent to $5.2 billion from $5 billion, and deposits increased 3.4 percent to $4.4 billion from $4.2 billion.

For the year, American Savings’ net income slipped 1.9 percent to $57.5 million from $58.6 million in 2012.