The King of the Fish

What is so special about yellowtail kingfish?

The genus which yellowtail kingfish (Seriola) belongs to is farmed in many places around the world. Yellowtail kingfish itself (Seriola lalandi) is farmed commercially in a few places, (e.g. Japan and Australia). The global demand is massive and the market prices are quite high. At the moment, NIWA scientists can grow a 3.5kg fish in a year.

“It is an attractive fish, it grows really fast and the market is ready for it. It is a premium sashimi and sushi fish, and it is delicious."

Dr Setiawan is confident about the future of the operation, saying because of the extent of the work that has already been done, it will be relatively easy to transfer the knowledge obtained from the research context straight to the industry. NIWA now has the green light to go from having just a research program on site to running an actual farm, which will be an on-land recirculating aquaculture system (RAS). 

Why is NZ investing in RAS?

“A good way to understand recirculating aquaculture is to think of an aquarium," says Dr Setiawan. "You have a set amount of water and it recirculates. Recirculating aquaculture is the same principle, but on an industrial scale. The idea is that you have a tank with a lot of fish and they need O2, secrete CO2 and produce waste. You process this water and you keep putting it back into the tank with a bit extra to compensate for evaporation. In a tight system like we have here, you should only need to replace 5% of the entire volume every day.”

He says because this is a closed system, a lot of factors can be controlled. The water coming in can be cleaned and also temperature-regulated to optimise the growth rate. The water coming out can also be treated, minimising the nutrients and other outputs going back into the natural ecosystem. This also greatly reduces, or even eliminates, the risk of pathogens coming in or going out of the farm. 

“Often in aquaculture research, things that work on a small scale are very different once you scale them up and this is where industries are wary if it will ultimately work for them. The scale of research we do at NIWA is what makes us different because we can use 5,000, 10,000 and 20,000-litre replicated tanks. This gives us the confidence that it’s going to work in the big 600 or 1,500 tonne farm.”

From fish egg to our plates

On site, seven tanks hold the kingfish broodstock, with around 20 fish in each tank and equal male/female ratios. Most of these are fish that were bred on site. They first breed at three years old, but become good breeders around five years old. The fish will typically reproduce between December and March, but this can be changed, since the photoperiod and temperature of the water can be controlled. 

“When the fish breed, the female will squirt out hundreds of thousands, sometimes up to millions of eggs. Multiple males will inseminate these eggs, which will then float to the surface and get collected. Each morning, we look at the quality of these and decide if we are going to use them or not. If they are good, we will disinfect and incubate them. It will then take two days for the eggs to hatch. After another two days, the staff can transfer them into the nursery area where they will start being fed.”

The fish are split up and transferred into larger tanks as they grow bigger. They can be harvested when they turn one-year-old and weigh between 2.5 and 4kg. That is the end of their journey on NIWA’s production side and they are ready for market. 

A small proportion of fish is selected for future brood stock: best growing, best traits, while avoiding inbreeding. These fish will be then be put on the brood stock diet and become breeders three to four years later. And so begins the next cycle.