Project description

Resource management and the circular economy were the overarching themes of the LeTe-Protein project. The aim was to generate new knowledge to close material cycles as far as possible - particularly in the area of regional fish fattening, where compound feed made from regional components was used. The aim was not only to utilise residual material sources, but also to refine them in a targeted manner. The research centred on the potential for cultivating duckweed(Lemna minor) using residual water from a closed aquaculture recirculation system. Parallel to this, rearing trials were carried out with flour beetle larvae(Tenebrio molitor) using by-products from herb and grain processing as a substrate.

The regionally obtained duckweed and flour beetle larvae were processed into high-quality protein sources and tested in feeding trials with regard to their suitability for use in fish nutrition. Producers of animal products are under increasing pressure as consumers are increasingly asking questions about the origin and production methods of food and the feed used. A key component of conventional fish feed is fishmeal, around 75 per cent of which is used in fish feed worldwide. Against this background, the project investigated the possibility of a sustainable and regional alternative to fishmeal.

The production of animal feed from products of closed cycle systems represents a potential for the future that has hardly been researched to date. The production of duckweed and mealworm larvae within such a cycle offers promising approaches for providing high-quality proteins for animal feed from regional raw materials. These crops make it possible to return wastewater from fish recirculation systems and plant by-products from primary agricultural production back into the animal feed cycle as valuable resources.

In view of a self-sufficiency rate of only around six per cent for edible fish in Austria, there is a considerable need to increase domestic fish production and develop suitable feedstuffs. Regionally produced protein sources such as dried duckweed in combination with flour beetle larvae meal offer a promising basis for a demand-orientated and efficient fish feed in Austrian fish farming. In the project, catfish(Clarias gariepinus) were selected as the model fish for the feeding trials.

Results

Two main approaches to utilising waste materials were pursued as part of the project. Firstly, the nutrient-rich residual water from the fish farm was used to cultivate duckweed. Production took place in two phases: initially in a test facility with an area of around eight square metres, and later in a facility extended to one hundred square metres. The duckweed showed very high protein contents of between 33 and 42.5 per cent in the dry matter. The harvest volumes increased continuously until the end of the project. However, it was found that duckweed tends to accumulate elements. In addition to high levels of sulphur, zinc and manganese, alarmingly high concentrations of arsenic, lead and cadmium were also measured, some of which exceeded the permissible limits of Directive 2002/32/EC.

On the other hand, the breeding of flour beetle larvae was optimised. The population was significantly increased and the husbandry conditions improved. Various by-products from herb and grain processing were tested as substrates. Rye green meal pellets in particular proved to be a suitable substrate for the beetles. In larvae fed with oil flax by-products, the proportion of omega-3 fatty acids was significantly increased - from the original 1-2 grams to up to 15-32 grams per 100 grams of fat.

The acceptance of the newly developed feed was tested in a feeding trial with brook trout(Salvelinus fontinalis). The test fish accepted the food well, but showed a conspicuous yellow-greenish colouration, particularly on the belly and fins. This change is presumably due to the high carotenoid content of the duckweed.

Benefits of the project

The LeTe-Protein project has laid the foundation for cycle-orientated and sustainable fish feed production. It shows how high-quality proteins can be obtained and utilised from regional raw materials. The results make an important contribution to the implementation of the Austrian Protein Strategy and promote a resource-efficient food supply chain. The focus is on the utilisation of by-products: around 5,000 cubic metres of fish waste water are produced annually in the Waldland aquaculture recirculation plant, while around 4,000 cubic metres of herb waste and 370 tonnes of grain waste are produced during herb and grain processing. These previously unutilised raw materials can be usefully fed back into the animal diet using the processes developed in the project. The concept not only offers ecological advantages, but also strengthens regional value creation and contributes to independence from global feed markets.

Further information

DaFNE - Research platform