Strength and corrosion resistance vital

As wild fish stocks decline globally, the spotlight is increasingly being shone on humane stun and slaughter methods in the rapidly growing aquaculture industry. Stainless steel components fabricated by Pryde Fabrication (ASSDA Accredited) are an integral part of a Brisbane innovation that is leading the way internationally in a shift towards faster and more humane automated percussive stun methods.

Seafood Innovations International Group Pty Ltd has spent around 10 years developing fish harvest technology which enables fish to swim naturally until the second they are stunned, reducing stress on the fish and improving flesh quality.

They have collaborated extensively during this period with Pryde Fabrication (Cleveland, Queensland) to develop the system, which incorporates a base, ramp and trigger plate made from grade 316 stainless steel.

Up to 400 of the units are being produced each year, of which around 98 per cent are for export.

Pryde Fabrication General Manager Darren Newbegin said Grade 316 stainless steel was chosen for the components primarily due to its corrosion resistance and strength. He said other design and fabrication requirements included:

• No bacterial traps
• Robust enough to withstand the harsh environment and repetitive shock loading
• Light enough to enable easy handling of the modules for cleaning
• Configured to enable easy dismantling for cleaning

“We never considered any grade other than 316 because of the harsh environment – the majority of the units are exported overseas, where they are being used in minus temperatures, fully immersed in sea water,” he said.

There is about 15kg of stainless steel in each machine, which is laser cut, enabling a high level of accuracy for both cutting and fold marks. The rest of the procedure is performed manually, including welding, polishing and glass bead blasting to provide a pleasing surface appearance.

“Stainless steel is the perfect material to laser because it’s so clean to cut,” Mr Newbegin said.

Seafood Innovations’ Business Manager Noel Carruthers said the development of the system had benefited from choosing a fabricator in the company’s local area, as it enabled a close collaboration.

Mr Newbegin agreed with this sentiment, suggesting it was this relationship between the two companies which had contributed to making the product fit for purpose and tailored to cost and operational efficiency.

“This relationship has allowed Pryde Fabrication to be involved in a solution to world fish farming and we are excited about further growth in this Australian initiative,” he said.

Mr Carruthers said the patented system represented an enormous change to the industry, with a single unit processing 15-20 fish per minute automatically, compared with other processes such as electrocution, carbon dioxide gas, and the use of wooden clubs.

The system works by pumping a current of water, which the fish are naturally inclined to swim towards. They then reach a point where their nose hits a trigger, which releases and immediately retracts a small, blunt-nosed piston at high speed, making the fish irreversibly unconscious. The fish are then turned upside down and enter a bleed machine where they are automatically bled.

In addition to improved flesh quality, the automated system means fewer operator injuries and immediate bleeding, resulting in improved appearance of fillets when fish are processed. The ability to slaughter at the point of capture means fish potentially carrying diseases will not contaminate other waters in transit.

Although originally developed for Atlantic salmon, the system has also been refined to cater for different varieties of fish, including tilapia, pangasius, barramundi, yellowtail kingfish and cobia.

A recent installation on a Marine Harvest vessel in Norway (incorporating three sets of a four channel system) is slaughtering 20,000 fish an hour at 98% efficiency.

The equipment has been independently tested by laboratories in Norway and ongoing developments to the system are tested at Huon Aquaculture in Tasmania.

The article featured in Australian Stainless Issue 47 - Spring 2010.