Higher revenue from international and commercial clients boosted Tetra Tech Inc.’s earnings in its fiscal first quarter.

After the markets closed Wednesday, the Pasadena engineering and consulting company reported net income of $22.3 million (36 cents a share), compared with $18.7 million (30 cents) a year earlier.

Revenue rose 13 percent to $611 million. Analysts surveyed by Thomson Reuters on average were expecting per-share profit of 33 cents on revenue of more than $406 million.

Tetra Tech provides mainly water and environmental infrastructure services to commercial and government clients.

Chief Executive Dan Batrack said new customers from its recent Canadian acquisitions and other international business helped revenue growth.

“International business increased significantly and now represents 25 percent of our net revenue” Batrack said in a statement. “In addition, commercial net revenue grew 11 percent year-over-year. The performance and opportunities in our international and commercial markets have improved our business outlook.”

Even so, Tetra said it expects second-quarter income of 25 to 29 cents a share and revenue of $375 million to $405 million, lower than the Wall Street consensus for

31 cents a share and revenue of more than $392 million.

Shares were down 57 cents, or 2.4 percent, to $23.65 in midday trading on the Nasdaq.