Increased demand for sustainable seafood and reduced technology costs are stimulating growth in indoor aquaculture, including two Atlantic salmon farms planned for midcoast Maine. Portland-based Whole Oceans announced plans Thursday for a $250 million indoor farm at the site of the former Verso paper mill in Bucksport. The news came less than a month after Nordic Aquafarms, a Norwegian company, released plans for a $150 million indoor salmon farm in nearby Belfast. The timing of Whole Oceans’ announcement was coincidental, said corporate development director Ben Willauer.