Introduction
Aquaculture is facing challenges in terms of environmental sustainability of the feeds used and susceptibility of the farmed organisms to diseases. Fish meal and fish oil are still commonly used in farmed species’ nutrition because of their nutritional value. Although most of these ingredients in the European Union are derived from well-regulated wild fish stocks and are certified, they are at the limit of sustainable exploitation. Moreover, particularly in some developing countries (e.g., China) with high levels of production, the use of these ingredients makes aquaculture practices associated with a high carbon emission. Given the high density in intensive farming systems, fish can be exposed to stress, which may have negative impacts on their immune system. Consequently, this effect will potentially deteriorate fish health and well-being, increasing the possibility of infection with pathogenic invaders, eventually leading to mortality. Functional ingredients possess bioactive compounds that regulate physiological processes and exhibit biological activities, which could improve weight gain, feed efficiency, and disease resistance in fish while reducing the environmental impacts of the sector. Accordingly, through the inclusion of novel functional ingredients in diets, such as the microalgae spirulina and the plant quinoa, may offer a potential solution to mitigate these issues.
This study aims to assess the effects of functional feeds on key growth performance indicators (e.g., weight gain, feed conversion ratio, feed intake), health (e.g., gut epithelium integrity, immune condition and oxidative status) of juvenile Nile tilapia (Oreochromis niloticus). Feeds were formulated with eco-efficient, circular economy-driven and organic frameworks.
Methods
Three experimental diets were formulated and produced by SPAROS Lda (Olhão, Portugal). A practical (PD) diet as control mimicking a commercial-type feed, without fish meal and fish oil. Organic (ORG) based on ingredients compatible with organic certification (including spirulina and quinoa). Eco-efficient (ALT) using circular economy-driven subproducts (e.g., poultry and feather meal) and emergent (e.g., spirulina, insect meal, quinoa) ingredients. Spirulina had inclusion levels of 10% and 2.5% and quinoa 5% and 2.5%, in ORG and ALT, respectively. All diets were formulated to be isonitrogenous (crude protein 39.4% wet weight (WW))and isoenergetic (gross energy, 19.2 KJ/g WW). The trial was performed in 12 tanks of 300 L (3 diets x 4 replicates) with an average temperature of 24.4 ± 1.2 ◦C (mean ± SD). Each replicate tank contained 30 Nile tilapia with an initial mean weight of 31.0 ± 0.5 g. Fish were daily fed with the experimental diets until visual satiation for 61 days. Growth performance indicators were assessed, including weight gain, relative growth rate, feed conversion ratio (FCR) and voluntary feed intake (VFI). Fish were sampled for whole-body composition analysis and dissected for liver, anterior and posterior intestine for assessment of immune condition, oxidative status and gut health. Diet apparent digestibility was also determined. Statistical analyses were performed using SPSS version 23.0 by one-way ANOVA, followed by Tukey’s post-hoc.
Results
Although fish were fed until satiation, the VFI and FCR significantly differed across diets (Fig. 1 and 2; p<0.05). Both indicators were within normal values for PD and ALT, but not for ORG, showing that fish exhibited a negative response, which was reflected in the performance indicators.
Fish that were fed diet PD exhibited higher weight growth (3.5 – fold increase), ALT roughly doubled their initial body weight, while ORG almost did not show any growth (Fig. 3). Similarly, the final body weight of PD was also 1.7-fold and 3.3-fold higher than diet ALT and ORG (p<0.05), respectively.
Conclusions
The three aquafeed formulations demonstrated significantly distinct impacts on juvenile Nile tilapia performance. Diets ALT and specifically diet ORG provided worse growth performance indicators than PD. The evaluation of the impacts of the diets on fish health (e.g., gut epithelium integrity, immune condition and oxidative status) is underway. In any case, this study reinforces the notion that novel formulations and ingredients need to be thoroughly evaluated.
Acknowledgements
This work has received funding from the European Union’s Horizon 2020 research and innovation program under the Marie Skłodowska-Curie grant agreement No 956129. This study also received Portuguese national funds from FCT – Foundation for Science and Technology through projects UIDB/04326/2020, UIDP/04326/2020 and LA/P/0101/2020 to CCMAR.