To achieve a sustainable Mediterranean aquaculture production, it is necessary to increase the production of low trophic species, such as Mugil cephalus, combined with aquaculture systems with low environmental impact, like Biofloc Technology (BFT). BFT is characterized by its minimal use of water, in which bacteria and other aggregates of microorganisms recycle nutrients, maintain water quality, and provide food for the animals. The objective of the present study was to evaluate the light restriction (24h darkness), use of probiotics, and interaction between these variables on the zootechnical performance of M. cephalus reared in BFT.
Material and Methods: For the experiment, 180 animals with an initial weight of 91.73 ± 22.4 grams were randomly distributed in 12 circular tanks of 800L of water (initial:150-200 mg/L of total suspended solids (TSS)). In order to study the light restriction and use of probiotics (Sanolife PRO-W Bacillus subtilis and B. licheniformis, 1g/m3 per week), 4 treatments were proved: 12-hour photoperiod (Light); light restriction (24h darkness; Dark); 12-hour photoperiod + probiotic (Light+Prob); and light restriction + probiotic (Dark+Prob). A commercial feed (DIBAQ - 3.5 mm for tilapia) with 30% crude protein and 7% crude fat was provided three times daily at a 2 %/d feeding rate.
Results and discussion: The results of the zootechnical parameters are described in Table 1. The different treatments showed no effect on the survival of M. cephalus, which was around 100% in all of them. Moreover, the treatments with the presence of light showed the highest feed conversion ratio (FCR), 12.42 ± 1.80 and 11.04 ± 2.25, and lowest specific growth rate (SGR), 0.18 ± 0.03 and 0.19 ± 0.04 to Light and Light+Prob, respectively.
On the other hand, although no significant differences were found in TSS among light and dark conditions, in general, higher values were registered in dark groups, what may have contributed to the better FCR and SGR of these treatments. Probiotics can stimulate the activity of digestive enzymes and thus promote better weight gain. This aspect, combined with the greater bacterial growth (higher TSS values) due to the darkness conditions, may have contributed to the good performance of the animals in the Dark+Prob treatment.
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 Conselleria d’innovació, Universitats, Ciència i Societat Digital of Generalitat Valenciana (GVA AICO/2021/198). J. Brol has a predoctoral grant from Generalitat Valenciana (Programa Santiago Grisolía 2021; CIGRIS/2021/109). R. Olivares-Perona has a technician contract was also funded by TED2021-129272B-C21. T. Cascales contract was supported by European Union Next Generation-Plan of Conselleria d’innovació, Universitats, Ciència i Societat Digital of Generalitat Valenciana (INVEST/2022/434).