Local Govt | National News Video | Parliament Headlines | Politics Headlines | Search


Looking for the ‘X factor’ in fish


Trout are spawning and its ‘talent time’ – looking for the ‘X factor’ in fish

It’s spawning time on the Rotorua lakes – when a few trout heading upstream find themselves hauled off into a fishy talent show!

Fish & Game staff know exactly what they’re looking for as they trap fish and screen out the biggest and best trout for their Big Fish Breeding Programme. These hand-picked (literally) specimens are the breeding stock used to raise more than 100,000 fish to keep North Island lakes stocked up for anglers.

The fish are trapped as they swim upstream to spawn – in a stream that flows into Lake Tarawera, known for its hard-fighting trophy trout. They are carted off to holdings pens in a stream which flows through Fish & Game’s Ngongotaha hatchery grounds.

A set of selection criteria are used to pick only the best fish as parents – a female to supply the eggs and “cross” with a male that’s used to fertilise them. The aim is to produce fish which are healthy and grow rapidly to a large size for anglers to catch.

Most of the fish used for breeding are three year-olds, along with a smaller number of four year-olds which are breeding for the first time. Trout stop growing once they reach maturity and spawn, so by selecting older maiden trout for breeding the hatchery improves the chance of their offspring growing bigger.

Previous spawners are often rejected because they have poorer quality eggs and these, Fish & Game officer Lloyd Gledhill explains, can be picked by signs such as the ragged edges on their fins where they’ve been digging redds (nests) in the gravel.

This year the largest fish appear to be around the 65cm to 68cm mark, so fish which are over 62cm fit the selection category for the time being. “Later in the season we might change the selection size depending on how the run is going. You never quite know how many fish might come in, and once they have been through the trap it’s too late to get more.

“If we don’t get eggs now, there’ll be no fish to release next year so the pressure in on” says Mr Gledhill.

After selecting for size, it comes down to a “judgement call” on the look of the fish. Mr Gledhill says you get fish that are different shapes including those which are “all head and shoulders” and tail off to the back. “I like a fish that’s a much more even shape all the way through. We look for robust, healthy fit fish.”

Fish & Game staff aim to end up with 135,000 viable fish, which means stripping an estimated 250 thousand eggs from the “ripe” hens. Every spawning season they “cross” a total of about 90 males with the same number of females, 180 fish in total.

“That gives us a good margin – some eggs die and others die at hatching so that gives a good number of viable fry at the end. It also ensures we get good genetic variety in the fish being released to the lakes.”

How are the eggs extracted? The fish are firstly sedated in a fish bin with a synthetic clove oil added, then a small gauge tube is inserted into the fishes belly cavity, and compressed air used to gently push the eggs out.

“The sperm activates as soon as it hits the water – so you’ve got about 20 seconds for the sperm to get to the egg and fertilise it.”

The eggs are taken inside the hatchery and placed into trays with running water piped over them, to begin the process of growing first into first “eye ova,” and then into fry.

When they’re big enough, the young fish are loaded into the ‘live trout truck’ and carted off for one of the many releases into North Island lakes.

© Scoop Media

Parliament Headlines | Politics Headlines | Regional Headlines



Relevant Consents Gained: Government Unveils RMA Reform Package

The government has formally hauled down the flag on its attempts to alter the balance of environmental and economic priorities in the Resource Management Act, unveiling a 180-page Resource Legislation Amendment Bill containing reforms that have been largely endorsed by most political parties. More>>


Closing Schools And Such: Interim Redcliffs Decision Announced

“While the school’s board has argued that circumstances that could give rise to potential disruption are extremely unlikely, advice from technical experts has shown these concerns cannot be ruled out." More>>


Jane Kelsey: High Court Can’t Make Groser Provide TPPA Information Faster

‘This week we went back to court to challenge Trade Minister Groser’s stalling tactics over the release of information on the Trans-Pacific Partnership Agreement negotiations, following a High Court order that he reconsider the Official Information Act request I made last January’, said University of Auckland law professor Jane Kelsey, first applicant in the case. More>>

Werewolf 58: No Climate For Change

The last time the global community tried to take collective action on climate change the world’s leaders finally came to agree that every not-too-onerous effort should be made to hold global warming to 2°C above the pre-industrial average. At Paris, all 150 participant countries nations will have put forward their pledges... On the information available, New Zealand's is the second weakest contribution of any nation in the developed world. More>>


Lambton Quay Shutdown: Object Was Made To Look Like Bomb

Police cordoned off part of Lambton Quay Wednesday afternoon, saying that a suspicious package had been found. Buildings were evacuated and buses were detoured. The army’s explosive ordnance disposal unit was brought to the Quay. More>>


Public Sector Still Shrinking: Record Low Number Of 'Backroom Bureaucrats'

Ongoing restraint in the public sector and a focus on better frontline services has seen a further reduction in the number of core Government employees, State Services Minister Paula Bennett says. More>>


Disobeying The Law: Police Censorship Of Crime Research “An Outrage”

The Green Party is calling on Police Minister Michael Woodhouse to ensure Police scrap controversial contracts that place onerous restrictions on academic researchers’ access to Police data, the Green Party says. More>>


Get More From Scoop



Search Scoop  
Powered by Vodafone
NZ independent news