Introduction
Biofloc technology (BFT) is an example of sustainable aquaculture due to its zero or minimal water exchange and its potentiality to reduce the input of artificial feed (fish meal) thanks to the establishing a nutritionally rich microbial biomass that can be used as natural food by the reared animals (Wasielesky et al. 2006). Mugilidae (especially Mugil cephalus) are excellent candidates for sustainable Mediterranean aquaculture due to its herbivorous/omnivorous feeding behavior. However, few information is currently available on the culture of this species in bioflocs combined with a reduction of fishmeal in the diet. Therefore, the objective of the present study was to evaluate the growth and nutritional efficiency of M. cephalus reared in bioflocs and fed diets containing reduced levels of fishmeal.
Material and Methods
For the experiment, 600 animals with a mean weight of 80 grams obtained from the Institute of Agrifood Research and Technology (IRTA, Tarragona), were transported to the facilities of Universitat Politècnica de València. The animals were randomly distributed in 9 tanks of 3.3 m3. Three isolipidic feeds (10%; Table 1) were tested in tanks in triplicate with decreasing levels of fishmeal inclusion (15, 5 and 0% corresponding to treatments HP15, HP5 and HP0, respectively). The ratio between essential amino acids (AAE) and non-essential amino acids (AAnE) was similar for the three feeds, being at 0.73 and 0.88. The animals were fed until apparent satiety three times per day (9:00, 13:00 and 17:00h). The water quality parameters were monitored during the whole experimental period, which had a duration of 27 days. Results were analyzed compared using one-way ANOVA and to significant differences between treatments were verified by applying the Newman-Keuls test (significance level of 5%). Additionally, at the end of the experiment, the effect of the diet on the intestinal microbiota was evaluated through the analysis of 16S ribosomal DNA.
Results and discussion
The mullets adapted quickly to BFT, and a total substitution of fish meal meant in lower survival whit significant differences (Table 2). Additionally, HP0 showed the highest feed conversion ratio (FCR) and the lowest protein efficiency ratio (PER) and specific growth rate (SGR), but without significant differences. Nevertheless, HP5 did not reported differences with HP15 neither growth nor survival.
In relation to microbiote composition, the phylum with the highest representation was Proteobacteria (43.76 ± 6.74%), followed by Firmicutes (18.78 ± 5.38) and Spirochaetota (16.19 ± 5.47%). HPO reported an increase of Firmicutes (31.14 ± 10.71 vs 1.23 ± 0.19 %) and decrease of Planctomycetota (5.38 ± 2.62 vs 16.04 ± 0.83 %) presence respect to the initial point. No differences were observed independently of the diet respect diversity alpha (Shannon-index).
Therefore, low fish meal inclusion levels are possible in M. cephalus under BFT without affecting zootechnical performance and intestinal health. Similar results were observed by Nhi et. al (2018) in Oreochromis niloticus, also an herbivore/omnivore species, being able to reduce fish meal inclusion into the diets under BFT.
Bibliography
Nhi, N. H. Y., Da, C. T., Lundh, T., Lan, T. T., & Kiessling, A. 2018. Aquaculture, 495, 654-660.
Wasielesky, W., Atwood, H., Stokes, A., Browdy, C.L., 2006. Aquaculture 258, 396–403.
Acknowledgments
This work was supported by European Union Next Generation-Plan de Recuperación-Ministerio de Ciencia e Innovación-Gobierno de España (TED2021-129272B-C21), and Generalitat Valenciana (GVA AICO/2021/198). J. Brol has a predoctoral grant from Generalitat Valenciana (Programa Santiago Grisolía 2021; CIGRIS/2021/109).