An aquaponics grower is having great success raising rainbow trout near Tamworth in north-west New South Wales, despite the fish being a cold water species.

Aquaponics is a closed farming system in which fish poo fertilises water that is then recycled to irrigate fruit and vegetables.

Space to play or pause, M to mute, left and right arrows to seek, up and down arrows for volume. Listen Duration: 5 minutes 39 seconds 5 m Rural Reporter: Cool trout in a warm climate Download 2.6 MB

Space to play or pause, M to mute, left and right arrows to seek, up and down arrows for volume. Listen Duration: 5 minutes 3 seconds 5 m Gordon Garradd is successfully growing rainbow trout in an aquaponics system Download 2.3 MB

Temperatures in Loomberah often reach the high 30s, but Gordon Garradd uses a water chiller to keep the temperature in his insulated fish tank below 21 degrees Celsius.

Solar power is used to pump the nutrient-laden water from the fish tank through a series of small garden beds — or grow beds — containing a range of vegetables.

The plants extract the water and nutrients they need to grow, cleaning the water before it is pumped back up the hill to the fish tank.

Gordon Garradd feeds rainbow trout in an insulated 9,500 litre tank.

Mr Garradd raises the rainbow trout in a 9,500-litre water tank, which is insulated by gravel and shaded by succulent plants and vines.

"Rainbow trout are a cold water fish and we're not in a cold climate here [but] with some help of some insulation and a water chiller, we're able to keep them over summer," he said.

Humane death for tasty trout

Mr Garradd harvests several trout at a time, catching them in a net at night when their vision is poor.

He then strokes their bellies which calms the fish before they are lifted from the water.

"They taste better killing them in a stress-free manner like that," he said.

Rural news in your inbox? Subscribe for the national headlines of the day.

The fish tank's filter collects the fish waste, which is then diverted to another tank and circulated through wicking beds where beans, sunflowers, zucchini, cucumbers and finger limes are grown.

A second system circulates water that has had the fish poo removed, through some other gravel grow beds that house broccoli, cabbages, corn and rhubarb.

"The aquaponics system is proving to be a lot more productive than growing in the soil, and uses a small fraction of the water," Mr Garradd said.

Grow beds are watered with water from the rainbow trout tank via a pipe. The water wicks from gravel at the bottom of the bed, through some geotextile cloth and up into the soil.

Mr Garradd's horticulturalist partner Hether MiLane is trialling a range of plants for use in the system.

There are two types of grow beds being used in the system at their Gunagulla Organic Garden.

"Underneath the straw, which is there to reflect sunlight, we've got soil to a depth of about 20cm, then a layer of geotextile, which is a fabric cloth to stop silt going through, and then under that we've got gravel, and that's where the water runs," Ms MiLane said.

"The water wicks from the gravel through the geotextile and up into the soil. The water comes in from the pipe at the top and then we've got a drain in the centre for it to drain out."

Marigolds are planted among finger limes to repel nematodes.

Space to play or pause, M to mute, left and right arrows to seek, up and down arrows for volume. Listen Duration: 4 minutes 18 seconds 4 m 18 s Organic farmer Hether MiLane is trialling assorted plants in an aquaponics system Download 2 MB

Marigolds have been planted in some of the grow beds in an attempt to tackle the detrimental effects of nematodes [microscopic worms that weaken plants and reduce productivity].

Ms MiLane said marigolds repelled nematodes and provided a habitat for valuable insects.

"The bright jazzy flowers of the marigolds also bring in a lot of natural predators, hoverflies, bees and wasps, that are really good at keeping pests under control," she said.

"And we've got lots of little birds that peck off aphids, scale, mealy bugs and that sort of thing, so we don't have to do any spraying."

Controlling pests using natural predators

An aquaponics greenhouse also forms part of the farming system at Gunagulla, where it is used to grow seedlings, herbs and tropical plants, and the predators of some of the farm's insect pests.

Allowing aphid numbers to build up on some kale, Ms MiLane said natural predators would control the pest population.

"We've got stacks of aphids but there are also parasitic wasps that sting the aphids," she said.