Introduction
One of the objectives of the Horizon Europe project NOVAFOODIES is to reduce the environmental impact of aquaculture by using more sustainable ingredients replacing traditional fishmeal or use of functional ingredients aiming to improve efficiency, productivity, etc.
Earlier studies have shown that macroalgae can be a promising source of proteins in fish feeds and have interesting functional properties, improving fish health and disease resistance. However, protein digestibility might be a problem limiting inclusion levels. Protein digestibility can be improved by fermentation of the biomass, however thus far experimental research on the use of fermented macroalgal biomass in fish feeds is limited. Macroalgal blooms and beach-wrecked macroalgae count with important populations of small invertebrates as crustaceans, isopods and amphipods feeding on them. Population densities can be extremely, making these also a potentially promising source of feed ingredients.
In this contribution we will present the results of a study testing the effect of four types of prime matter in two different nutritional trials with Atlantic sea bass (Dicentrarchus labrax). In a first trial, artificial diets were formulated with either invertebrate meal (3% mixture of small isopods and small crustaceans growing on Ulva spp.) as a protein and fatty acid source or meal of the brown macroalga Ericaria amantacea (2%) and tested against a control diet (commercial sea bass feed). In the second trial, two levels of inclusion of fermented and non-fermented Ulva sp. biomass (5 and 10% respectively), replacing fish meal were tested against the same commercial diet.
All feed ingredients were subjected to rigorous analyses, evaluating proximate composition, detailed fatty and amino acid profiles, biosafety analyses (e.g. heavy metal levels, etc.) and functional properties (e.g. antioxidant activity, anti-microbial activity). After extrusion, physical properties of the feeds were analysed (e.g. density, deformation load, etc.). During the nutritional trials, diet effect on fish performance (growth, health indicators) was evaluated and after the trials, blood samples were taken from the fish to study immunological indicators.
Results and discussion
First trial: invertebrate mixture and E. amantacea meal. The invertebrate mixture was characterized by their high protein (35-40% dw) concentration, whereas protein content of E. amantacea was considerably lower (7%). Fatty acids were relatively low (4-5 % dw), however, they were in majority poly- and monounsaturated fatty acids.
E. amantacea showed important antioxidant activities, most likely related to their high content in polyphenols. Both invertebrates and E. amantacea demonstrated significant bacteriostatic activity on fish pathogens Photobacterium damselae subsp piscicida and Lactococcus garvieae, limited effects on Vibrio anguillarum and Aeromona veronii and no significant bacteriostatic effect on Tenacibaculum maritimum.
Fish fed the inverbrate or Ericaria diet showed no significant differences in growth rate or feed conversion compared to the control diet, as could be expected considering the limited addition. With respect to immunological parameters, both experimental diets showed significantly increased antioxidant activity compared to the control diet. The results of the first trial showed that invertebrate biomass in particular had important nutritional and functional properties that merit further studies to evaluate incorporation in fish feed as a substitute for fish meal.
Trial 2: non-fermented and fermented Ulva sp. biomass grown in nutrient rich IMTA systems. Fermentation process was optimized earlier in the NOVAFOODIES project. Fermentation significantly increased protein content of the Ulva (from 37 to 45% dw) and lipid content (from 0.13 to 0.66% dw). Both non-fermented and fermented Ulva showed bacteriostatic effects on all five pathogen straints tested. Effects were generally slightly stronger for fermented Ulva and the most pronounced effects were found for Tenacibaculum maritimum and Lactococcus garvieae. Preliminary effects of the fish trials indicate slightly reduced growth at the highest Ulva inclusions, however final results are needed for a definite conclusion. After the finishing of the nutritional trials, fish will be subjected to a physiological stress test and a bacterial challenge.
Acknowledgments/Funding
This study has been carried out as part of the project NOVAFOODIES, which has received funding from the European Union under Grant Agreement N° 101084180.