Phosphorus is one of the most important minerals required by fish.Due to low concentration of phosphorus in natural waters,and low absorption rate of phosphorus from the water,fish must obtain most of phosphorus from their diets.The optimal amount of phosphorus supplementation in commercial feeds is important not only economically,but also for environmental reasons.Phosphorus metabolism in cultured aquatic species has become a popular research subject,due to rising concerns about phosphorus discharged into aquaculture environment.The present experiment was conducted to evaluate the effects of dietary phosphorus on growth performance,body composition,bone mineralization and blood chemistry index of juvenile rice field eel(Monopterus albus).Five practical diets were formulated to contain graded levels(0.67%,0.91%,1.05%,1.29% and 1.53%)of phosphorus from dietary ingredients and monocalcium phosphate.Each diet was randomly fed to triplicate groups of fish with initial mean weight of (34.4±0.3) g in floating cages(1.5 m×2.0 m×1.5 m)to apparent satiation for 70 days,and each cage was stocked initially with 100 fish.The results showed that:(1)fish weight gain rate(WGR),protein efficiency ratio(PER)and feed efficiency(FE)increased with increasing phosphorus from 0.67% to 1.05%(P<0.05)and then plateau over the level of 1.05%.Broken-line analyses[Y=104.67-46.07(1.10-X),R²=0.944]suggested that optimum dietary phosphorus content is 1.10% based on WGR.(2)whole-body protein contents and condition factor(CF)were significantly elevated,however,whole-body lipid contents as well as hepatosomatic index(HSI)were significantly reduced by increasing dietary phosphorus.(3)Diet phosphorus level can sighnificantly enhance the content of whole-body ash and phosphorus(P<0.05).Broken-line analyses[Y=0.988-0.635 4(1.05-X),R²=0.928]suggested that fish fed diets with phosphorus of 1.05% presented highest whole-body phosphorus content.both vertebrae phosphorus and calcium contents increased linearly with increasing dietary phosphorus levels while vertebrae Ca/P ratio was not influenced.Broken-line analyses[Y=7.696-0.985 5(1.10-X),R²=0.956]indicated vertebrae phosphorus content showed highest values at the diet phosphorus of 1.10%.(4)Dietary TP had distinct effects on P,Ca and alkaline phosphatase contents in serum.This research revealed that 1.10% dietary total phosphorus was required for maximal tissue storage and mineralization as well as optimal growth.