The company's lawyers say unless they can feed out more pellets at Clay Point from October to December they will have to starve fish, cull fish or harvest them too small for the market, reports Marlborough Express.
In a letter attached to the application, lawyers Quentin Davies and Peta-Claire Brunel said these options would be cruel to fish or result in losses for the company.
King Salmon chief executive Grant Rosewarne said fish at Clay Point needed more feed because they were bigger than usual this season and there were more mouths to feed.
Last year King Salmon was looking at a lower than usual harvest, partly because of high deaths at Waihinau in Pelorus Sound and partly because fish bred in 2010 and 2011 had poor survival rates and a poor ability to convert feed to flesh.
To make up tonnage, the company delayed harvesting at Clay Point and other farms, Mr Rosewarne said.
Not only did fish grow bigger but there was a bigger overlap between crops, meaning more mouths to feed for longer, he said.
The company had a pleasant surprise when the 2012 fish grew faster than expected and had a high survival rate of about 98 per cent compared with a 75 to 85 per cent average. Again, this meant they needed more feed.
Meanwhile, the company had split its Pelorus fish farm which usually rotated between Waihinau and Forsyth Bays, Mr Rosewarne said.
"If we can keep fish relaxed and calm, putting on the same weight or more, and eating less feed with less impact on the environment that will be a great result."
Fish farmers in other parts of the world separated age classes but this was new to King Salmon, he said. If successful, the approach would be extended to new farms.
This week King Salmon was harvesting fish at Forsyth. The site would be fallowed until at least May next year and ideally longer if the company could get new sites up and running.
These were approved by the Environmental Protection Authority and High Court but had been appealed to the Supreme Court by environmental groups Sustain Our Sounds and the Environmental Defence Society.
King Salmon's application to increase feed at Clay Point by 500 tonnes between October and December this year goes to an open hearing on October 10 and 11.
The company has also applied for a backdated increase in feed used at the farm in 2011-12, when it broke the rules on how much feed it gave its fish, and for three years from December. Only previous submitters can submit on these changes and a proposal to rewrite rules for effects on the seabed.
Resource management officer Bruno Brosnan said the council could not take legal action against King Salmon for overfeeding fish at Clay Point until these applications had been processed.