Production of fish feed from vegetable waste (VG13050)

What was it all about?

This project investigated the feasibility of using vegetable wastes to grow insect larvae that could in turn be used as feed for use in aquaculture. As consumption of fish and seafood in Australia grows, there is a need for the aquaculture industry to turn to efficient alternative food sources and meal made from insect larvae has been proposed, since insects are high in protein and fat, can be reared on waste products, and are part of the natural diet of some farmed fish species.

The researchers began with a literature review of four possible insect species. One, black soldier fly, was found to be most promising. Larvae can grow on vegetables alone and, once their pre-pupae stage is reached, they climb up and out of the damp organic matter, making it simple to harvest them at the right time. Adult flies are commonly found in Australia, although they originated from the US. They are not pests, don’t carry disease and they live only long enough to produce the next generation. They have already been found suitable for feeding to a number of fish species and are currently being commercialized in several countries.

The researchers conducted a series of small trials to find out how easily black soldier fly can be reared in captivity, what vegetables they will eat, and how the quality of dried larvae compares to commercial fishmeal.

The insects proved challenging to rear through the complete lifecycle but with trial and error the research team established specific requirements for mating and egg laying.

Key findings from these breeding trials found that larvae feed on pumpkin, carrot, eggplant, capsicum and processed vegetable sludge. Researchers estimated that around 25g fresh pumpkin or 30g fresh carrot would be needed to produce each gram of dried larval meal. The ratio was further improved by adding ground flax seed to the diet – this doubled the rate of weight gain and reduced the volume of fresh feed required by around 70 percent.

The researchers concluded that a significant amount of research is still required before this method could be commercialised. It has, nonetheless, generated information and methods that can be built on in a larger research trial, which would be the next step.