Performance of Mugil Cephalus under a Biofloc technology system (BFT) with light restriction and probiotic addition

The flathead mullet, Mugil Cephalus, is an estuarine species classified as low trophic scale, known for its ability to adapt to different environmental conditions. The aim of this study was to evaluate the growth performance, the survival rate and the potential of this species on BFT system (Biofloc technologies) under different environment condition. Over a duration of 41-day, M. Cephalus juveniles (91.73 ± 22.4) were reared into four different environment status: 12-hour photoperiod (Light); light restriction (24h darkness; Dark); 12-hour photoperiod + probiotic (Light+Prob); and light restriction + probiotic (Dark+Prob). Following this phase, a second stage of 47 days commenced, during which the microalga Chlorella vulgaris was introduced into the light-exposed tanks. At the conclusion of this stage, the fish were divided into two groups to evaluate the resilience of M. cephalus under stress conditions induced by density (high stocking density) and a combination of density stress with reduced oxygen levels. During all the experiment Mugil Cephalus was stocked in tanks of 800L of water and water quality parameters were monitored every day. Fish were feed with an artificial feed for marina fish (2% of the total biomass). It was observed that the different treatments showed no effect on the survival rate of M. Cephalus, the mullets adapted positively to the Biofloc. Regarding the different treatments, it has been established that the treatments with the presence of the light showed the highest feed conversion ratio and lowest specific growth rate. On the other hand, although no significant differences were found in total suspended solid among light and dark conditions, in general, higher values were registered in dark groups, what may have contributed to the better Feed Conversion Rate (FCR) and Specific Growth Rate (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.