Effect of Biofloc Culture on the Daily Rhythmicity of the Activity and Expression of Digestive Enzymes in Tilapia, Oreochromis niloticus.

Biofloc technology (BFT) has recently attracted great attention due to minimal water exchange and reduced feed intake. This study aimed to recognize daily changes in the digestive physiology of Oreochromis niloticus between a traditional system and BFT. The enzyme activity of trypsin (try), chymotrypsin (chy), leucine aminopeptidase (lap), alkaline proteases (alk), lipase (lip), and amylase (amy), along with the gene expression of trypsin (try), chymotrypsin (chy), pepsin (pep), amylase (amy), and phospholipase (pla) were measured throughout a daily cycle. Samples were taken every 4 h in a 24 h cycle under a 12:12 L:D photoperiod. During 60 days, fish were feed three times a day (zeitgeber time, ZT: 0, 4, and 8) with a fishmeal-based diet containing 32% of crude protein and 5% of lipid, where molasses was added as a carbon source in BFT. No significant differences were found in fish performance among treatments at the end of the experiment. The activity of all tested enzymes significantly (p < 0.05) increases during the dark period in both treatments, where the same activity pattern was found in try and lip. The maximum expression levels of digestive gene enzymes between treatments show a marked effect dependent on the presence of light and dark phases. The cosinor analysis showed an activity in try, lap, and lip with a significant rhythmicity (p < 0.05). Our results demonstrate that some processes related to the digestive physiology of tilapia that respond directly to daily rhythmicity are modified under the constant presence of feed in BFT. These findings should be considered when establishing new optimized culture protocols.