"Lake Okataina may again produce the largest two-year-old trout while we expect Rotoiti to provide some stunners," says Eastern Fish and Game's Matt Osborne in Rotorua.
The warmer winter lakewater temperatures will have produced better-than-average growth, and fisheries officers are looking forward to seeing how fish size compares at the start of the season.
They are hoping for better catch rates at the start of the new season on Tuesday - thanks to a new approach to releasing hatchery-bred rainbows aimed at boosting survival rates.
The method was introduced after a 2010 trial on Lake Tarawera where fish were released in smaller monthly batches instead of three big liberations over the year. It showed that conditions in May and September releases can harm survival rates.
"We learned seasonal conditions make a difference. If colder winter weather comes earlier than expected during May, or is delayed into September, there can be dire consequences for newly released trout." "Improving survival rates through this staggered method will lead to better catch rates."
Fish & Game also had the results of a PhD study of smelt and trout in Lake Rotoiti, which showed there were some large seasonal differences in smelt quantity and quality, and this further supported changing to the staggered release method.
Most trout caught at the opening on the big lakes - Tarawera, Okataina and Rotoiti - are two-year-old fish that have been released as 12-month-old fingerlings, growing quickly to about 2kg in just 12 months.
More fishing action on Rheem Outdoors with Geoff, 5pm Saturdays, TV3, and at www.GTTackle.co.nz