Lake Rotoiti produced the biggest fish, including a trout of more than 4kg, on the opening weekend of the new fishing season.

The season kicked off on October 1, the first time in five years the opening had fallen on a weekend - with school holidays in full swing.

Fish & Game Officer Matt Osborne said anglers fishing in the well-named Lake Rotoiti Monster Trout Tournament caught seven fish that weighed in well over 3kg, with the biggest a solid trout that was 67cm long and 4.1kg, caught by Mitchell Tombleson.

Another three of the entries were quality fish that weighed 3.5kg or more, he added.

Overall, Lake Okataina was the standout performer with the best catch rate of the three lakes that reopened - Okataina, Tarawera and Rotoiti.

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"We measured nearly 150 fish brought in by just over 100 anglers at Okataina and the 2-year-old fish that were mostly caught were on average 51cm and weighing 1.65kg."

The busiest lake as usual was Tarawera, with a total of 364 anglers interviewed about their catches; the catch rate on the day was slightly ahead of the 2015 opening.

The 2-year-old rainbows caught were larger than last opening and their condition was better, Mr Osborne said, averaging 49cm and 1.36kg.

"Some positive signs were seen in the number and size of the smelt (a key food) which were found when the fish were gutted."

The largest fish that staff measured from Lake Tarawera was a modest 3-year-old trout that weighed 2.4kg.

Mr Osborne said the Ohau Channel started fairly well and in total, 51 anglers were surveyed who had kept 49 fish.

The largest was a 66cm brown jack which weighed 3.88kg.

Meanwhile, Fish & Game Officer Anthony van Dorp said only a couple of anglers were found to be breaking the rules on opening day - similar to previous openings when one or two offenders were usually intercepted.

One angler was fishing without a licence while in another case, two men were trolling with three rods out - which is against the rules - you can only use one rod per angler.

Mr van Dorp's message to anglers is there are some sportfishing rules to be followed so "don't take chances - play fair".

He said given opening day was the one day you can expect to run into Fish & Game rangers, it would be pleasing to see "100 per cent compliance".