Williams said obvious size limit changes were needed for snapper and kingfish.
"Frankly, no fin fish should be harvested under a size at which they are fully sexually mature."
Williams said a 30cm snapper produced five times as many eggs as a 25cm sexually-mature snapper.
But not all snapper were ready to reproduce upon reaching 25cm, he said.
Williams also suggested gradually introducing a three per cent royalty on all commercial fishing revenue over the next decade.
"If our fisheries are managed properly, they should be a huge source of income and enjoyment for all of us," he told the Petitions Committee today.
National's Simon Watts, MP for North Shore, asked about fin fishing and links between size limits and fish maturity.
Williams said his research took account of reproduction rates, and his suggestions would lead to more fish in the ocean and greater genetic stability.
"Larger population sizes are...generally more resilient to other external factors, whether that be climate change or selection pressures, such as us."
MP for Nelson, Rachel Boyack of Labour, said her home town had a big fishing port and she wanted to know about on-board camera debates.
Williams mentioned how last year Minister for Oceans and Fisheries David Parker said up to 300 inshore fishing vessels would get cameras by the end of 2024.
He said that was a good start and should help protect some endangered species such as Hector's Dolphin.
MPI fisheries management director Emma Taylor said the ministry at this stage had no plans to change size limits.
Taylor pointed out recreational daily bag limit rules which came into force today.
Rules for daily limits on recreationally caught finfish now include species that previously had no limit.
Parker last month said of more than 1000 finfish species, only 43 were previously subject to a daily recreational fishing limit.
Specified baitfish and freshwater eels still had their own separate limits - six freshwater eel per person per day, and 50 specified baitfish per person per day.
National's Jacqui Dean, MP for Waitaki, said she had concerns about catch quotas for blue cod in southern parts of the country.
Meanwhile, the Fisheries Amendment Bill had its first reading in the House of Representatives.
Parker said the bill would strengthen and modernise New Zealand's fisheries management system to create a more sustainable, higher value operating model.
He also said it would better incentivise commercial fishing practices or good commercial fishing practices.
The bill proposed to introduce new graduated offences and rules to improve the effectiveness of onboard cameras.
"We want to ensure the long-term health and resilience of our ocean and coastal ecosystems, including the role of fisheries," Labour MP for Te Tai Tonga Rino Tirikatene said.
Green Party list MP Eugenie Sage said a more rapid rollout of cameras on boats was needed.
"It's not good enough just to prioritise the Māui dolphin fishery because of the concerns about the impact of trawling on Māui," she said.
National supported the bill but had some concerns.
"Most Kiwis would agree that a sustainable ocean environment is something that we should all aspire to have," National's MP for Waikato Tim van de Molen said.
But he said there should be discussion on amending rules for what fish must be landed and what must be returned.
