Sustainable Aquaculture Feeds and Feed Additives in Aquaculture
Fish farms are often publicly criticised for using unbalanced, large amounts of food additives and antibiotics and the perception that economic interests are more important than maintaining sustainability and animal friendly conditions. Therefore, there is a demand for new, more sustainable “prime matter” food sources that can be used as the main protein source in fish food instead of less sustainable ingredients such as fish meal. Furthermore, new feeds should stimulate more efficient digestion in the fish, reducing the amount of excretion to the environment and thereby the phosphorus (P) and nitrogen (N) load of these farms. In addition, there is also a need for functional ingredients that improve fish health and resistance to disease in addition to improving the nutritional profile of the fish for the final consumers.
Aquaculture Feeds in the SIMBA Project
SIMBA is addressing these objectives as part of Task 2 of the marine microbiome work package (WP3) of the project. Danish project partner, Fermentation Experts, have been developing and optimising sustainable protein sources based on formulations of fermented soy, rapeseed and seaweed that contain viable lactic acid bacteria. Portuguese partners, NECTON and ALLMICROALGAE have been working on optimization of the cultivation of the microalgal species Chlorella vulgaris, Nannochloropsis spp. and Tisochrysis lutea that serve as potential functional feed components.
Within SIMBA, we are testing the performance of these components separately in comparison with fish fed a standard commercial diet. Project partners designed a total of five experimental diets: two diets with a 50% substitution of fish meal with two different fermentation products and three diets containing an addition of 2% phytoplankton. The effects of these diets are being tested in nutritional fish trials by partners NIVA (Norway), LUKE (Finland) and CTAQUA (Spain). The trials cover the three main European fish aquaculture species: marine salmon (NIVA), freshwater salmon (LUKE) and sea bream/ sea bass (CTAQUA).
Image 1. Fish tanks systems in CTAQUA
What We Measure and Why
To evaluate the performance of the experimental diets, partners are analysing general fish performance parameters such as growth, biometric indicators and general health indicators. Using fish weight gain and feed administered, the efficiency of the feed (the conversion ratio of feed biomass into new fish biomass) is calculated. In addition, water samples are analysed to evaluate a potential reduction of the nutrient charge to the environment in the experimental feeds. A number of fish are being sacrificed and their intestines sampled for study. SIMBA partner MATIS (Iceland) is analysing microbiome composition of these samples as an indicator of the fish gut environment. Potential health stimulating effects are evaluated by analysing fish immune system indicators in the blood. Finally, fish fillets are being analysed and compared between diets for their nutritional composition (protein content, total lipid content, fibre content, etc.). One important compound to assess is the amount of (poly)unsaturated fatty acids, such as omega-6 fatty acids. As these are abundantly available in some microalgae, it is hoped to see the effect of these diets in the resulting fish fillets.
First Results with Sea Bream and Sea Bass
CTAQUA has now finished their nutritional trials in the two fish species sea bream and sea bass, both of which are especially important in southern European Atlantic and Mediterranean aquaculture. So far, the team has analysed all performance parameters and part of the immune system indicators. These first results will be presented in an e-poster at the upcoming Aquaculture Europe 2021 conference in Madeira, Portugal.
In sea bream, fish growth rate and feed efficiency were about 10% lower for one of the fermented products in comparison to the control diet, whereas there was no significant difference for the diet containing the other fermented product. Fish growth in diets containing phytoplankton was not significantly different compared to the control diet. For sea bass, performance of both diets containing fermented products were significantly reduced by 10 – 15%, whereas for the phytoplankton addition again no differences were found.
Analyses of most relevant non-specific immune indicators are currently in progress. First results of the non-specific immune indicator lysozyme activity showed higher values for the diets containing fermented compounds and the microalga Chlorella in both fish species, however the differences were not significant compared to the control diet. A consistent significant decrease of lysozyme activity compared to the control diet was observed in diets containing Nannochloropsis sp. and Tisochrysis lutea.
Image. Erik Malta and José Cabello checking on fish tanks in the CTAQUA facilities in Spain
Additional analyses of non-specific immune indicators, fillet composition and composition of the intestinal flora are underway. Current results indicate that addition of phytoplankton to fish feeds does not impact nor improve general performance, whereas effects on immune indicators might be species specific. Partial substitution (50%) of fish meal protein by fermented products, in particular compound EP299 had no negative impact in the case of sea bream and a slight reduction in performance in sea bass. This might be due to the specific feed preferences of these species: sea bass is an almost exclusively carnivorous species, whereas sea bream is much more omnivorous and is known to feed on seaweeds and detritus. Considering the very high substitution of the fish meal by fermented compounds, these results are encouraging, suggesting that an important part of fish meal can be replaced by more sustainable compounds. It will be very interesting to see whether the experimental diets had effects on the other parameters and what they will do for salmon.
By Erik Malta and José Cabello, CTAQUA, Spain.