Fish Feed From Vegetable Waste

Adult Black soldier fly (Hermetia illucens).

Adult Black soldier fly (Hermetia illucens).

Australian consumers love fish and seafood with consumption doubling over the last 10 years, and expected to continue to grow. However, most aquaculture species are fed, at least in part, on fishmeal made from wild caught fish, which is not only unsustainable, but also a major factor limiting increased production. Meal made from insect larvae has been proposed as an alternative. 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. This article reviews an Australian study that examines the potential use of vegetable wastes to grow insect larvae, which can then be used in aquaculture and aquaponic feeds.


A few years ago I investigated the potential to grow yabbies (a freshwater crayfish native to Australia) in a ‘closed’ system using selected kitchen vegetable waste (mainly legumes and carrot), a precursor to establishing a sustainable aquaponics system. The project was ‘sparked’ by the seasonal supply and high cost of wild sea lobster. Following a discussion with a local chef about the dwindling supply of wild lobster, he said he would include the sweet-tasting yabby on the restaurant menu, if only he could source a reliable supply. At the time, a literature study revealed Australia only produced a small quantity of commercial yabbies (Cherax species) annually. Most are grown in farm dams primarily used for watering stock; but if you want to sell the yabbies, then you need a permit from your state’s Fisheries Department, with restrictions moving them between states to preserve the health status of existing stock —yabbies, like all crayfish, are susceptible to the parasite Thelohania and fungal disease.

Yabbies are detritus feeders; that is, they feed on dead plant or animal matter. However, for higher than natural production, supplementary and more frequent feeding is essential. While some commercial yabby farmers supplement the natural feed with lupins, others use commercial marron pellets, which can improve yabby growth by 85%. However, feeding yabbies marron pellets and other wild caught fishmeal products makes commercial yabby production unsustainable.

More recently, Dr Jenny Ekman and her research team from Applied Horticultural Research Pty Ltd (AHR) completed a desktop study to evaluate the potential of using vegetable waste to grow insects, which could then be used to wholly or partially replace wild caught fishmeal in aquaculture feeds (HAL project VG13050). The AHR team conducted some initial trials to examine the suitability of different vegetables for producing black soldier fly larvae, and the researchers describe some of the issues that need to be addressed in commercialising this method in a 76-page report.

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 insects studied by the AHR research team were Black soldier fly (Hermetia illucens), Yellow mealworm (Tenebrio molitor), Superworm (Zophobas morio) and the common housefly (Musca domestica). Of these, black soldier fly (BSF) was a clear frontrunner. Larvae can live on vegetables alone and ‘self-harvest’ when they are fully mature. Adult flies are found naturally in Australia, they are not pests, they don’t carry disease, and only live long enough to mate and lay eggs. The researchers conducted a series of trials to find out how easily BSF can be reared in captivity, what vegetables they can eat, and how the quality of dried larvae compares to commercial fishmeal.

An initial colony of BSF was generated from local wild populations and grown through to adults. Although adults have been widely reported to not eat, the flies only mated and laid eggs once they were provided with apple juice. Feeding trials with 2nd generation larvae showed that pumpkin, carrot, eggplant, capsicum and processed vegetable sludge were all readily consumed. The study found that they could live on lettuce for only a short time, and these larvae had much higher water content than those fed other foods. The study found that cauliflower and broccoli were not suitable, and sweet potato was non-preferred.

The AHR team found it difficult to calculate the exact amount of feed required to produce the maggots because they liquefy feed before eating it. Despite this, estimated feed conversion rates of vegetable:larvae were obtained, which ranged from 4.9:1 to 2.0:1, averaging 3.3:1 (dry weights). This means that around 25g fresh pumpkin or 30g of fresh carrot would be needed to produce 1g of dried larval meal. The ratio was further improved by adding ground flax seed to the diet, which doubled the rate of weight gain and reduced the volume of fresh feed required by around 70%.

An economic analysis indicated that BSF is currently a risky option for an individual vegetable grower, with more research needed before this method can be confidently commercialised. The report’s author concluded that as the price of wild caught fishmeal continues to increase, financial viability will become more likely. The AHR research team noted that commercial facilities are now being developed in other countries, and these will help provide better guidance about how to grow and use these fascinating animals.

The rise of aquaculture
Consumption of fish and seafood in Australia has doubled in the last 10 years and currently stands at around 13kg per person year. This has been predicted to increase to 17kg by 2020 and 25kg per year by 2050, giving a total domestic requirement of 1.15kt annually. Given falling wild catches, aquaculture needs to double by 2020 and double again by 2050 to meet this demand, the report notes.

In the period 1970–2008, the production of fish from aquaculture increased at an average annual rate of 8.3%. This is in comparison with poultry and livestock meat production at an average rate of 2.7% per year (FAO 2010). Currently, about one third of aquaculture production consists of highly carnivorous fish (e.g. salmon, sea breams and barramundi). If the aquaculture sector is to sustain its current growth rate, then the supply of production inputs will also have to grow at a similar rate to meet demand.

One of the major factors restricting increased use of aquaculture is that most production systems rely on feeding high value aquaculture species on relatively low value wild caught fish. This is not sustainable in the long term, and has led to a search for alternative sources of high protein, high fat food sources. These have included cottonseed meal, legume crops such as lupins and soy, meat, bone meal and poultry wastes.

The AHR report notes that aquaculture species can’t live on plant-based feeds alone, which have problems with poor palatability, presence of anti-nutrients (e.g. phytic acid), intolerance to complex carbohydrates and deficiencies in essential amino acids. Animal-based foods are better but also have problems, such as poor consumer acceptance, high levels of saturated fats, absence of omega-3 fatty acids, and issues with food safety from rendered animal meal.
Insect-based protein meals such as BSF offer an alternative to plant and animal-based fish food as ingredients in fish food for aquaculture, but rearing methods and processing need to be refined to allow commercialisation, says the report.

Overseas commercial BSF production
The commercial production of BSF is already underway in some countries. It took three years of R&D before EnviroFlight (Ohio, USA) successfully achieved commercial production of BSF in 2012. Flies are maintained at 30 degrees Celcius with between 30-50% RH for different parts of the process. The company developed a (patented) system for encouraging mating. Adult flies are enclosed in tall, cylindrical wire cages inside a heated, humidified glasshouse. Lidded plastic containers with oviposition attractant are at the bottom of each cage. As part of the process the company plays music to the flies (Barry White, apparently), which generated substantial publicity in itself.

Much of the initial production has been sold to zoos and pet owners for feeding to animals as diverse as armadillos, sun bears, birds and bush babies. However, the business is expanding and aquaculture feeds are the clear long-term target. Processing involves rendering the larvae to extract the oil, boosting protein content to more than 70% DW.

While testing is still being conducted in tanks located at the facility, the company suggests that their product will be a suitable feed ingredient for rainbow trout, yellow perch, bass and bluegill. It is unclear whether production is already used for this purpose.

Organic Value Recovery Solutions (Georgia, USA) has developed the Organic Value Recovery System process, which is designed to convert waste streams including food waste, manufacturing residuals, manures, brewers grains and other organic wastes to BSF meal. Vegetable wastes are included in this, although the AHR team notes that no specific information is given and no results with vegetable wastes are provided.

It appears that the major supply from the Organic Value Recovery Solutions process is currently to herpetology enthusiasts (through the partnered company The Phoenix Worm store). However, this is a sideline to their major interest in aquaculture feeds and use of the method to dispose of wastes —particularly from intensive pig production.

The company claims that it is possible to replace 25-30% of the fishmeal in salmon diets with milled BSF pre-pupae, although it notes that higher percentage replacement would be possible if chitin (a derivative of glucose) is removed. The company states that channel catfish can be produced solely using BSF meal.

The primary business of Organic Value Recovery Solutions appears to be developing BSF production for companies with waste issues, rather than producing BSF itself. Major clients are intensive animal feeding operations. For example, they are currently involved in setting up a 100 ton processing facility for pig manure in South Africa. The facility itself is expected to be 10m x 60m, depending on the mating success percentages of the local BSF strain used.

The AHR research team enquired about the feasibility of setting up a similar facility for vegetable wastes in Australia. The company suggested that the best way forward is to conduct an initial feeding trial with the feedstock they have in mind. This would provide information on feed conversion rates and therefore the facility size needed and the financial viability of the operation, which is exactly what has been proposed as the next stage of the AHR project.

Other commercial production companies include Enterra Feed (Vancouver, Canada), founded by entrepreneur Brad Marchant and well known geneticist an environmentalist, David Suzuki. Enterra Feed grows black soldier fly larvae on what they describe as a fixed recipe comprising pre-consumer food wastes of vegetables, fruit, grains and fish. The company offers a service whereby they will collect certain kinds of food processing and grocery store waste.

The larvae are grown in an indoor heated environment and used to produce three main products—Grubbinz (whole dried larvae), feed meal, which is a processed meal derived from the larvae containing 55-60% protein and 15-17% fat, and extracted oil. It is interesting to note that ‘Grubbinz’ are recommended for feeding to poultry, tilapia and catfish, but as no more than 30% of the diet by dry matter.

Although the (patent pending) process to grow the larvae has been developing since 2007, Enterra Feed appears to have only begun commercial supply in October 2013. The company has gained extensive publicity due to its connection with David Suzuki.

AHR trial system
For the AHR study, three Biopods® (Protoculture LLC) were purchased to establish an initial breeding colony of black soldier fly. According to the manufacturers, using the Biopod can help turn 100kg of kitchen scraps into 15-20kg of BSF larvae. Given the relatively high moisture content of most kitchen scraps (~80%) compared to the pre-pupae (~56%), this suggests a feed conversion ratio close to 2:1.

To start the process, the manufacturers suggest simply filling the Biopod with some vegetable scraps and placing it in a shady area under warm conditions. This will attract female BSF if they are present in the environment. The presence of larvae attracts other females, who also lay eggs, establishing the colony.

One of the Biopods was therefore loaded with kitchen scraps and ground coffee and placed outside, in Sydney, during December 2013. Within two weeks larvae were visible. These were divided between the other units, also placed outside. It was quickly apparent that, at this time of year in Sydney, the colonies were self replenishing. New larvae appeared regularly and pre-pupae self harvested into the collection bucket.

The units were sustained with a continual supply of fruit and vegetables (supplied by Fresh Produce Group) or used coffee grounds and vegetable waste (supplied by local cafes). The larvae had voracious appetites.The AHR team noted that an entire ‘Qld Blue’ pumpkin was consumed within two days in one unit.

Black soldier fly larvae feeding on capsicum.

Black soldier fly larvae feeding on capsicum.

Apart from dark liquid waste discharged from the base of the biopod, remarkably little residue appeared to remain after processing by the larvae. The one part they were unable to consume were plant skins, such as those on pumpkin or capsicum. The flesh would be liquidised and completely eaten, leaving behind a clean, thin, papery skin.

Having established BSF populations outdoors from wild stock and harvested pre-pupae, the next step was to produce a breeding colony from which eggs and/or larvae of known age and provenance could be harvested for trials. The harvested pre-pupae were loaded into shallow trays loosely covered with mulch and placed inside an insect proof net house erected inside a glasshouse at Sydney University Darlington campus.

Self-­‐harvested black soldier fly prepupae.

Self-­‐harvested black soldier fly prepupae.

Temperatures during the trial remained warm, rarely falling below 15 degrees Celsius at night and generally increasing to between 25-30 degrees during the day. Temperature and humidity were also recorded inside the net house. Temperatures inside the greenhouse generally remained 2-3 degrees warmer than the outside air overnight. During the day, temperatures inside the house ranged from 3–10 degrees warmer than outside, or even more, the cooling system inside the greenhouse being inadequate to cope with hot weather.

Future research
The AHR report notes that CSIRO recently announced the development of Novacq™ as an additive to prawn feed. This sustainably produced product has been shown to improve prawn health and increase growth rate by 30% without compromising taste or quality. This bioactive growth stimulant took 10 years to develop, and involved a large research team and many $millions. The product is now licensed to Ridley AgriProducts in a deal potentially worth $billions.

The AHR report concludes that the development of BSF as an aquaculture feed has barely begun with major investment needed if this is to be commercially developed. Dr Ekman’s team notes that while a diet rich in vegetable wastes could clearly be part of this process, it seems unlikely that vegetables alone can provide fast and efficient enough growth to make this method economically viable. Consideration also has to be given to the fat, protein and other component profile of the dried meal in terms of its suitability for aquaculture species.

The AHR report highlights that further research needs to be funded by a university or a large commercial partner such as an aquaculture feed supplier, with possibly overseas expertise, if the commercialisation of BSF is to progress beyond this initial stage.

This project has been funded by Horticulture Australia Limited (HAL) using the vegetable industry levy and matching funds from the Australian Government. Ω

November 2014 / Issue 149