Growth, intestinal health, body composition, and molecular mechanism of the hybrid grouper, E. lanceolatus♂ x E. fuscoguttatus♀juveniles reared with microalgae Chlorella pyrenoidosa

The effects of microalgae Chlorella pyrenoidosa on the hybrid groupers' (Epinephelus lanceolatus male x E. fuscoguttatus female) growth, gut microbiome, and transcriptome were examined in this study. Feeding trials with a duration of 15 days (15d) and 60 days (60d) were conducted on three experimental groups (n = 3) as follows: (T1) grouper fed with basal diet and reared in filtered seawater (control treatment); (T2) grouper fed with basal diet and reared in C. pyrenoidosa monoculture water (CMW); and (T3) grouper fed with basal diet partially replaced with 15% of dried C. pyrenoidosa (CRM) and reared in filtered seawater. The findings revealed that groupers reared 15d in T2 treatment (T2-15d) had a higher fat content, with an apparent shift of microbial composition and functional pathways in the gut. Groupers reared 60d in T2 treatment (T2-60d) displayed an increased NADH dehydrogenase and cytochrome c oxidases gene expression, indicating more robust oxidative phosphorylation activity and ATP production crucial for metabolic homeostasis. The reduction in the total amino acid content was also detected in groupers raised in T2-60d. Gastritis, enteritis, and lipid malabsorption syndrome were observed in groupers raised 60d in T3 treatment (T3-60d), with the condition likely due to a higher intake of omega-6 to omega-3 fatty acids ratio in groupers raised 15 days in T3 (T3-15d) and T3-60d. All signs of intestinal inflammation may arise from the inclusion of dried C. pyrenoidosa. Overall, outcomes from this study revealed that introducing live C. pyrenoidosa to the culture water is advantageous for digestion and enhances the energy metabolism of juvenile groupers.