Effects Of Short-term Starvation And Re-feeding On Nile Tilapia(Oreochromis Niloticus,Linnaeus 1758):Growth,Immunity,Metabolism,and Intestinal Microbiota

Starvation can be led by environmental changes in the aquatic environment.During seasonal changes,fish undergo a shortage of food in their natural habitats or aquaculture.Most fish species withstand starvation and maintain the body‘s energy for their survival and growth by adjusting their metabolism and behaviors.But starvation in Nile tilapia,Oreochromis niloticus with respect in the intestinal microbiota,activities of digestive enzymes and other immune responses remain incompletely understood.In this study,the impacts of starvation and refeeding on growth,metabolism,immunity,and intestinal microbiota of Nile tilapia were evaluated.Healthy Nile tilapia fingerlings were randomly divided into two groups: control/fed group and starved group respectively under the same rearing condition for 21 days.The fish were allowed to acclimatize for two weeks.After starvation,the starved group was re-fed to satiation with a commercial feed(re-fed group).Biometric measurements including weight gain percentage(WG %),weight loss percentage(WL %),condition factor(CF),hepatic somatic index(HSI),and body weight(Q)were assessed in the fed and starved/re-fed groups.Phase 1 of the sampling days/times between the fed and starved groups is 0,3,7,10,14,and 21 days.Phase 2 consists of the fed group and re-fed group and the sampling times are 21,28,35,and 42 days.The bodyweight of fish significantly decreased during starvation and significantly recovers after re-feeding(P < 0.05).The hematological parameters such as white blood cells(WBCs),hemoglobin(Hgb),hematocrit(Hct),and red blood cells(RBCs)significantly increased(P < 0.05)after 14 days of starvation while the re-fed group significantly decreases within the successive times(P < 0.05).About the physiological and metabolic response,blood glucose significantly decreases under the starvation condition and significantly increases within successive times after re-feeding(P < 0.05),while the levels of cortisol,lactate dehydrogenase(LDH),and pyruvate kinase(PK)significantly increased in the starved group while the re-fed group was significantly maintained within successive times.Moreover,metabolic parameter including aspartate aminotransferase(AST)and alanine aminotransferase(ALT)in the starved group significantly increased during starvation and decrease after re-feeding.Leptin was also down-regulated d in the starved group and later upregulated in the re-fed group.Additionally,immunological parameters in the serum including immunoglobulin(Ig M)and antiproteases increased significantly after 21 days of starvation but decrease significantly in the re-fed group.The protease and lipase in the starved group decrease significantly during starvation but increased after 21 days of re-feeding.Nonspecific immune parameters(lysozyme,[LZM],and antioxidant enzymes including superoxide dismutase(SOD)and catalase(CAT)] significantly increased after 14 days of starvation(P < 0.05).During starvation,the immune-related genes(SOD,CAT,and hsp 70)significantly expressed and decreased after re-feeding respectively.Moreover,starvation led to significantly increase the diversity and abundance of Nile tilapia during starvation.The most dominant phyla found are Fusobacteria,Actinobacteria,Bacteroidetes,Proteobacteria,and Firmicutes.However,Actinobacteria,Firmicutes,and Proteobacteria significantly increased the starved/re-fed group while Fusobacteria and Bacteroidetes significantly increased in the fed group(P < 0.05).The most dominant genera found are Cetobacterium,Bacteroides,Lactobacillus,Bifidobacterium,and Plesiomonas.In the starved group,the identified functional pathways were mainly energy metabolism,amino acid metabolism,carbohydrate metabolism,nucleotide metabolism,and lipid metabolism while the re-fed group includes ABC transporters,histidine metabolism,and phosphotransferase system.In summary,this study investigated the impacts of short-term starvation and re-feeding on growth,metabolism,immunity,and intestinal microbiota of Nile tilapia(Oreochromis niloticus).These data will contribute to a better understanding of fish immunity and adaptability response to starvation-stress and provide a reference for optimizing the present management during fish culture.