This research aimed to evaluate the effect of biofloc technology on the intestinal morphometry, productive performance, and survival of juvenile Mugil cephalus. An 87-day investigation was conducted with two treatments, each with three replicates. Treatment one involved rearing juvenile M. cephalus in a biofloc system with a C/N ratio of 15:1, and treatment two involved rearing juvenile M. cephalus with a water exchange and no carbon addition. Ninety (90) juveniles of Mugil cephalus with an average weight of 117.36 ± 6.48 g were randomly distributed into six (6) circular plastic tanks of 250 L (fifteen fish per tank). At the end of the experiment, 10% of each experimental unit’s population was sacrificed for intestinal morphometry analysis. The productive performance was evaluated every 30 days by randomly sampling fish from each tank for biometric measurements, including the specific growth rate (SGR), feed conversion ratio (FCR), condition factor (K), and survival. No structural changes were observed in the intestinal mucosa. The fish reared in biofloc exhibited a similar gut morphometry (villus length and villus thickness) compared to the fish in the water exchange system. The biofloc system does not compromise the gut health of mullet. No significant differences (p > 0.05) were observed in the final weight, weight gain (WG), daily weight gain (DWG), specific growth rate (SGR), condition factor (K), and survival between the treatments evaluated. M. cephalus can be reared using biofloc technology, demonstrating significant water savings compared to water exchange systems.

In this work, we describe lesions produced by the dinoflagellate protozoan Amyloodinium ocellatum on the gills of Mugil liza, which causes the velvet disease in several fish species. These parasites produce severe lesions in the gills, with hyperplasia of primary and secondary gill lamellae rupture of pillar cells, and hyperplasia of chloride cells (ionocytes). The gill structure is totally affected, which presumably impairs normal hematosis and electrolyte regulation and seriously compromises the fish's health. The lesions caused by A. ocellatum are responsible for high mortality rates in fish farms and economic losses in the industry. In the present study, we found cellular hyperplasia of the respiratory epithelium, epithelial disruption, the collapse of secondary lamellae, and various degenerative changes that seriously compromise the gill functioning.