Fish meal is a highly demanded resource when it comes to the production of formulated feed for fin fish aquaculture and furthermore in general it is an important source of protein. But in times of a biodiversity-, climate- and energy crises new paths for its provision have to be taken.
The implementation of the Austrian “Strategic Plan 2020 for Aquaculture” caused an increase in domestic production volumes of edible fish. At the same time the amount of fish slaughter by-products has increased. Most of the remains are processed away from the production site. Considering that the slaughter yield is around 50% per individual, a high percentage is eliminated from the on-farm production cycle for human consumption.
In the frame of the project “Sustainable utilization of fish carcasses for the circular economy in Austrian aquaculture“ (No. 101742) financed by the Federal Ministry for Agriculture, Forestry, Regions and Water Management of the Republic of Austria and DaFNE, the processing of fish slaughter by-products is one of the main tasks besides a sociological study to clarify the potential of local aquaculture development scenarios and the interest in local fish meal production.
Materials and Methods
To process fish slaughter by-products of the African catfish (Clarias Gariepinus, Burchell 1822) a prototype of the Swiss company “Value Recovery Solutions AG” was tested – the further named “VRS Jumbo”. This machine can process 250kg of wet by-products by comminution, water evaporation and sterilization within a time span of 7 to 11 hours. After a cool down period the final products are a liquid (“fish oil”) and a solid component (fish meal). Several parameters of the default settings were adapted in the testing phase for the following experiments: In a first run 7 x 200kg fish slaughter by-products (carcasses, skins, fish-offals, heads – randomly collected) of the African catfish were processed. From the received fishmeal, samples have been put into high density polyethylene cans and these have been stored at -20°C until further analysis. The wet chemical analysis was conducted at the Feed Laboratory Rosenau – Regional Chamber of Agriculture, Lower Austria - while the amino acids were analyzed at the Institute of Animal Nutrition, Livestock Products, and Nutrition Physiology at BOKU- University, Vienna.
For the second part of the study – the sociological investigation for pin-pointing clearer directions of local aquaculture developments – consultations and opinions of stakeholders have been analyzed. For the narrative interviews three clusters of persons were targeted: (1) administration and legislation, (2) education and consulting and (3) fish producers. For each cluster a specific interview guideline was developed whereas the first question was in all three clusters covering the potential of Austrian aquaculture. The other question-blocks were specific for each cluster and its operations. Several dates were offered for persons from each cluster to participate in an online discussion. The meetings were recorded and further transcribed, analyzed and evaluated.
Analysis of the first runs of the production of African catfish meal revealed that (all values are mean values of the 7 analyzed procedures) the dry matter content (DM) is 92.1%, the crude protein content (XP) is 43%, the convertible energy is 18.62 MJ ME, the crude fat content (XL) is 30%, the crude fibre (XF) is 0.4% and the crude ash content (XA) is 17%. In comparison to other commercial fish meal (60-65% XP) the African catfish meal has a lower protein content, but it has more energy and fat, while crude fibre and crude ash are reduced.
The evaluation of amino acids shows that the ratios are similar to other commercial fishmeal. Especially lysine and methionine as the first limiting amino acids in fish meal present a mean of 2,57 g/100g (lysine) and 0,79 g/100g (methionine).
Within the sociological study limited or missing research results are