Such fine fishing can't be natural

Big trophy fish are said to abound in Rotorua's lakes. ELEANOR BLACK visits a hatchery and finds out that Mother Nature has been getting a hand.

It's not quite as easy as shooting fish in a barrel, but it's as close as any hungry angler can reasonably expect.

Rotorua's lakes provide some of the sweetest fishing spots in the world, luring the faithful with the promise of plentiful, fat trout.

Regulars are rarely disappointed.

But they may be surprised to learn their success rate is not a result of skill so much as the efforts of the Ngongotaha trout hatchery.

It is here that 150,000 rainbow, brown, brook and tiger trout are bred each year for release to the region's 14 lakes and to be shared with other communities, destined for the greedy hooks of angler's lines.

At nearly a year old and about 15cm long, thousands of spotted and multicoloured trout are ready for their autumn release. Thousands more will follow in spring.

Hatchery officer Marlia Fraser, who watches her charges develop from eggs stacked in trays to swift swimmers in large outdoor ponds, says the aim of the hatchery is to produce "big trophy fish."

The region's lakes are the product of volcanic activity and, with the exception of Lake Rotorua, feed short streams which are not suited to wild trout reproduction.

"While the lakes are exceptionally good for growing fish, there are very limited spawning opportunities," explains fisheries officer Rob Pitkethley.

The hatchery, set up in 1938 and run by the Eastern Region Fish and Game Council, fills the void.

Fertile female trout collected from the lakes are stripped of their eggs between May and August, when hatchery staff gently squeeze their soft, heavy abdomens, releasing ova into a basin.

The trout are returned to the lakes unharmed.

Each kilogram of trout yields 1000 eggs, and these are mixed with milt from male trout.

Now fertilised, the eggs are poured into fresh water and left to harden for 20 minutes before being scooped into incubator trays and left for 18 days.

When they have developed eyes, the ova are transferred to square metal baskets.

Staff shake the baskets vigorously as if they are sifting flour, a process called shocking.

Only the strongest eggs survive and the others - which look like tiny poached eggs - are removed.

When the fish hatch, unfurling and slipping through the weave of the basket, they are caught in a trough, where they lie for about 20 days until they have absorbed the nutritious yolk sac they carry on their bellies and start to swim.

They soon move to ponds outside and their fins are clipped for identification. When they finally head to the lakes, the trout are primed for a major growth spurt.

Not to mention a starring role on dinner tables throughout the country.