Dietary Phosphorus Requirements Of GIFT Tilapia (Oreochromis Niloticus) At Different Water Temperatures And The Effects Of Phosphorus On Its Physiological Metabolism And Intestinal Microorganisms

This experiment was conducted to investigate the effects of the interaction between water temperature and dietary phosphorus level on the growth performance,body composition and serum biochemical indices of GIFT tilapia,Oreochromis niloticus.Thus,the requirements of dietary available phosphorus for this fish at different water temperatures were determined.We also analyzed the effects of dietary phosphorus on liver metabolism of tilapia by using LC-MS/MS to measure liver metabolites.Meanwhile,the number of sequences,estimated OTU richness(ACE and Chao1),and diversity index(Shannon)for 16 S r RNA libraries of the mid-gut also analyzed.The main findings of the study are as follows.1.The aim of this study was to investigate the effects of temperature,dietary phosphorus level and their interaction on the growth of GIFT tilapia.Six groups of isonitrogenous and isoenergetic diets were formulated with calcium dihydrogen phosphate as phosphorus source,with available P content of 0.15%(control),0.38%,0.61%,0.83%,1.06% and 1.29%,respectively.GIFT tilapia.The test fish with initial body weight of(4.52±0.19)g were reared at 22℃,28℃ and 34℃,respectively,for 8weeks in an indoor recirculating aquaculture system(RAS).The results showed that weight gain rate(WGR)and specific growth rate(SGR)of GIFT tilapia showed a trend of increasing and then decreasing with the increase of the available P content in the diet under the three temperature conditions,and the feed conversion rate(FCR)showed the opposite trend;The hepatosomatic ratio(HSI),viscerosomatic ratio(VSI)and condition factor(CF)of tilapia in experimental group were significantly higher than those in control group,and were gradually decreased with the increase of dietary P level(P<0.05).Under the three temperature conditions,the crude protein and ash contents in body and muscle of GIFT tilapia increased with the increase of available P level,while the crude lipid content.showed a decreasing trend.The P content of the fish and the calcium and P content of the serum showed a trend of increasing and then decreasing with the increase of the available P level of the feed.There was an interactive effect of temperature and available P level on alkaline phosphatase(ALP)activity and total cholesterol(T-CHO)content in the serum of GIFT tilapia(P<0.05).Using the weight gain rate(WGR)of tilapia as an evaluation index,the optimum dietary available P levels for GIFT tilapia were obtained to be 0.82%,0.78% and0.76% at water temperatures of 22℃,28℃ and 34°C,respectively.2.The present study was employed to investigate the effects of dietary phosphorus levels on the growth and physiological metabolism of the GIFT tilapia.Three isonitrogenous and isoenergetic diets with total P content of 0.26%(low P treatment),0.81%(moderate P treatment)and 1.51%(high P treatment)were prepared by using calcium dihydrogen phosphate as phosphorus source.Each diet was one treatment with 4 replicates and 30 fish in each replicate.The fish with initial weight(8.42±0.09)g were fed with the test diets for 8 weeks in an indoor recirculating aquaculture system(RAS).The results showed as follows: weight gain rate(WGR)and specific growth rate(SGR)of tilapia in P moderate treatment were significantly higher than those in Low and high P treatments(P<0.05),and feed conversion ratio(FCR)of tilapia in P moderate treatment was the lowest.The hepatosomatic ratio(HSI),viscerosomatic ratio(VSI)and condition factor(CF)showed a gradual decrease with the increase of dietary phosphorus level.Dietary phosphorus level had a significant effect(P<0.05)on the apparent digestibility of dry matter,crude protein,crude lipid and phosphorus in GIFT Tilapia,and they showed a trend of increasing and then decreasing with increasing dietary phosphorus level.A total of 200 differential metabolites were screened in the low P treatment compared to the moderate P treatment,of which 174 were down-regulated,mainly amino acids and their metabolites,organic acids and their derivatives;26 were up-regulated,mainly fatty acyl groups and glycerophospholipids.A total of 87 differential metabolites were screened in the high and moderate P treatments,of which 75 were down-regulated,mainly amino acids and their metabolites;12 were up-regulated,mainly organic acids and their derivatives,and amino acid derivatives.KEGG annotation and enrichment analysis of differential metabolites showed that the main metabolic pathways of down-regulated differential metabolites were cyanuric acid metabolism,biosynthesis of gluconate ester,alanine,aspartic acid and glutamate metabolism,and most of the upregulated differential metabolites were mainly enriched in the metabolic pathway of fatty acid synthesis in the fish in low P treatment compared those in moderate P treatment;most down-regulated differential metabolites were mainly enriched in the following metabolic pathways: arginine and proline metabolism,phenylpropionic acid biosynthesis and most up-regulated differential metabolites were mainly enriched in the metabolic pathways of amino sugars and nucleotide sugars in the fish in high P treatment compared those in moderate P treatment.3.The present study was employed to investigate the effects of dietary phosphorus levels on the intestinal microbiome of the GIFT tilapia.Bacterial diversity in the midgut of test 2(metabolism)tilapia was determined using 16 S amplicon sequencing.The results were as follows: The number of OTUs was ranked as: high phosphorus treatment(1352)> medium phosphorus treatment(1157)> low phosphorus treatment(966),the increase of dietary P content increased the number of intestinal flora of tilapia.Ace,Chao1 and Shannon indices indicate that the abundance and diversity of tilapia gut flora show an increasing trend with increasing dietary P levels.Firmicutes,Actinobacteria,Proteobacteria and Bacteroidota were the dominant phyla in the intestinal flora of tilapia.The abundance of beneficial bacteria such as Romboutsia and Cetobacterium was the highest in the moderate P treatment,while the abundance of Mycobacterium and Bacteroides tended to decrease with increasing P content in the diet.Dietary phosphorus can improve the abundance and diversity of bacteria,and benefit the intestinal health.