The growth response fish exhibit to different feeds has made aquaculture one of the most effective means to produce animal proteins for consumption. This has been made possible through a combination of selective breeding, optimised feeding and the use of modern feeds in today’s farmed fish. However, the ecological impact arising from increased production, the limited availability of raw feed materials and factors relating to animal wellbeing tip the scales in the opposite direction when it comes to farmed fish being a truly sustainable source of food.
Solutions expected from fish feed
When it comes to the production of food from aquaculture, expectations for fish feed are high considering the major short-term growth potential high quality fish feeds can have. On one hand, environmentally ‘safe’ feed is required to minimise negative environmental impact, while on the other hand, feed needs to be easily digestible and fulfil the nutritional requirements set for farmed fish. Considering that a product needs to be low cost and increase growth rapidly, while also being healthy and tasty, the list of required properties long.
The partial replacement of fishmeal and fish oil used in feed, with plant-based proteins has been at the core of feed research and development for more than twenty years now. Alternative raw materials have included maize, textured vegetable protein, wheat, broad bean, and turnip rape and rapeseed oil amongst others
One challenge in the use of these alternative plant-based raw materials is their anti-nutrient compounds, such as phytates, saponins and trypsin inhibitors. To reduce anti-nutrient compounds in feed, raw materials can be pre-processed in various ways. The digestibility of phytate phosphorus in plant-based raw materials can be improved by adding phytase, produced using Bacillus bacteria, to feed. Other pre-processing methods applied to plant-based raw materials include peeling, heat treatment, extraction, and fermentation.
Feeding trials in progress
One of the goals of the international SIMBA project, funded by the EU Horizon 2020 programme, is to produce and test alternatives for fish-based raw materials in fish feed. Between September and November 2020 feeding trials were conducted on Atlantic salmon in Luke’s Paltamo unit. The aim was to use standard feed and two different test feed products, in which half of the fish-based raw materials contained by standard feed were replaced with lacto-fermented plant-based raw materials (supplementations manufactured by Fermentationexperts AS, feed by SPAROS). Fermented soy-seaweed accounted for 30% of soy-based feed, and fermented rapeseed made up 15% of rapeseed-based feed. All three feed products had the same volume of total energy, raw fat and raw proteins (22.4 MJ/kg, 22% and 44.1% respectively). Feeding trials are also being conducted in Spain (CTAQUA) and Norway (NIVA) using feed products with a similar composition. The fish species being used in these tests include sea bass, sea bream and Atlantic salmon.
In many studies, the replacement of fish-based raw materials with plant-based ingredients has been proven to reduce growth in fish. Therefore, determining suitable additive levels for fish, without endangering their growth and health, continues to be one of the most important focus areas in feed research. In the feeding trials conducted in Paltamo, fish groups that consumed test feed products were compared with a fish group eating a standard feed product. As all tested fish were tagged with a Passive Integrated Transponder (PIT), individual growth and condition could be monitored throughout the trial. At the ten-week mark, all fish were weighed three times and their general condition was noted.
Since the results obtained so far have been very promising, fish group monitoring and sampling will now be continued until the end of 2021.
Health effects from diets – for fish and people
In addition to fulfilling nutrient requirements, the new feeds aim to provide other positive health benefits for fish. For example, the fermented additives contained by the test feeds will improve the microbial composition in the intestines of fish, even in the short-term
The initial assumption is that, as health-improving lactic acid bacteria modify microbiomes in the intestines of fish they will take over living space from harmful microbes, antioxidant, anti-inflammatory and antimicrobial metabolites. Equally intermediary products from metabolic reactions could increase the number of useful bacteria and improve the resistance of the fish to different pathogens. In our feeding trials, the possible changes in microbiomes are studied from gut samples taken from different fish groups. The determination of the species-specific composition is based on metagenomics, i.e. the identification of species based on DNA determined from samples.
One of the goals of the SIMBA project is to increase our knowledge of the on the nutritional requirements and produce information about the health effects of innovative feed products on fish. The knowledge and use of microbiomes may also assist in the farming of micro- and macro-algae, and seaweed biomass. It might also assist in the production of feed raw materials. Seaweeds are rapidly growing plants that convert large volumes of carbon dioxide into oxygen, they are generally regarded as the food of the future for both people and animals. Because seaweeds are sources of polyunsaturated fatty acids necessary for fish growth, it is possible that they would be better alternatives for fish feed than the plant-based raw materials currently being used. In addition, they could have a positive impact on the wellbeing of not just fish, but also us as consumers.