Studies On Nutritional Metabolism Of Juvenile Tiger Puffer (Takifugu Rubripes) In Response To Stocking Density And Dietary Levels Of Protein And Phosphorus

Three feeding trials were conducted to evaluate the effects of dietary protein,phosphorus content,and stocking density on growth performances,body composition,biochemical indices,and relevant physiological processes of tiger puffer(Takifugu rubripes).The results of these studies are shown as follows:1. Effects of dietary protein content and stocking density on growth performance,nitrogen excretion,and relevant biochemical parameters of juvenile Takifugu rubripesIn this experiment were studied using juvenile tiger puffers with an average initial body weight of 15.60 g.A two-factor,three-level(2×3)design was used,with three different protein levels(38.87%,45.55%,and 51.00%dry matter)and stocking densities of 1.53 kg/m~3(20 fish in a tank of 0.196 m~3volume),2.30 kg/m~3(30 fish per tank),and 3.06 kg/m~3(40 fish per tank).The feeding trial was conducted in an indoor flow-through system.Each diet was fed to triplicate tanks for 8 weeks.The results showed that,at a certain stocking density,low dietary protein resulted in lower weight gain compared with the medium and high dietary protein levels(P<0.05).Neither dietary protein content nor stocking density significantly affected body proximate composition of experimental fish.At a certain dietary protein level,high stocking density increased total protein and total cholesterol contents in serum compared with medium stocking density(P<0.05).The total protein in serum was higher in the low-protein group than in the medium-protein group(P<0.05).The activity of alkaline phosphatase in serum was significantly higher in the low-protein group than in the high-protein group(P<0.05).No significant interaction was observed between the effects of dietary protein content and stocking density on growth performance and nitrogen excretion.Ammonia nitrogen excretion in the high-stocking-density group was higher than that in the low-stocking-density group at 3 hours after still-water feeding(P<0.05).Results of this study suggest that 45.55%dietary protein was sufficient to maintain normal growth in tiger puffers.Dietary protein content and stocking density had no significant interaction in the effects on growth performance and ammonia nitrogen excretion.Under the condition of this experiment,the suitable dietary protein content was 45.55%,and the suitable stocking density was 2.30kg/m~3.2. Effects of dietary phosphorus content and stocking density on growth performance,phosphorus excretion,and relevant biochemical parameters of juvenile Takifugu rubripesIn this experiment were studied using juvenile tiger puffers with an average initial body weight of 14.98 g.A two-factor,three-level(2×3)design was used,with three different phosphorus levels(0.68%(LP),0.98%(MP),and 1.31%(HP)of dry matter)and stocking densities of 1.53 kg/m~3(20 fish in a tank of 0.196 m~3volume,LD),2.30kg/m~3(30 fish per tank,MD),and 3.06 kg/m~3(40 fish per tank,HD).The feeding trial was conducted in an indoor flow-through system.Each diet was fed to triplicate tanks for 8 weeks.The feeding rate at the LD level was significantly higher than that of the MD level(P<0.05).The weight gain at the HP level was significantly higher than that at the LP level,and that in the LD level was significantly higher than that at the HD level(P<0.05).At 3 hours post feeding(static water after feeding),the concentration of active phosphate and total phosphorus in the rearing water at the HP level was significantly higher than that at the MP and LP levels,and that at the MP level was significantly higher than that at the LP level(P<0.05).The concentration of active phosphate in the rearing water at the HD level was significantly higher than that at the LD level(P<0.05).The total phosphorus concentration in the rearing water at the HD and MD levels was significantly higher than that at the LD level(P<0.05).The fish crude lipid content in the LP group was significantly higher than that in the HP group(P<0.05).The fish crude protein content in the MP group was significantly higher than that in the HP group(P<0.05).The ash content of whole fish in the HP and MP groups was significantly higher than that in the LP group(P<0.05).The content of calcium and phosphorus of whole fish in HP and MP density phosphorus levels was significantly higher than that in LP levels(P<0.05).Serum total cholesterol,high-density lipoprotein cholesterol,low-density lipoprotein cholesterol and alkaline phosphatase in the LP group were significantly higher than those at MP and HP levels(P<0.05).The content of serum phosphorus at the LP level was significantly higher than that in at the HP level(P<0.05).The content of serum vitamin D3 at the HP and MP levels was significantly higher than that at the LP level(P<0.05).The content of parathyroid hormone at the HP level was significantly higher than that at the LP level(P<0.05).The content of serum cortisol at the LP level was significantly higher than that at the HP level(P<0.05).Feed phosphorus content and culture density had significant interactive effects on serum cortisol,vitamin D3,calcitonin,parathyroid hormone,spine calcium and phosphorus content,whole fish calcium content and water active phosphate concentration.The results showed that,LP(0.68%)and HD(3.06kg/m~3)could inhibit the growth of puffer fish.The increase of phosphorus content in feed and culture density will increase phosphorus excretion in the rearing water.The increase of feed phosphorus content significantly reduced the fat accumulation in whole fish body and serum of juvenile puffer fish.The deficiency of phosphorus content will lead to the decrease of mineralization and affect the metabolism of calcium and phosphorus in the serum.Feed phosphorus content and culture density had significant interactive effects on calcium and phosphorus metabolism of juvenile puffer fish.Under the condition of this experiment,the suitable dietary phosphorus content was 0.98%,and the suitable stocking density was2.30kg/m~3.3. The effects of fish protein hydrolysate replacing fish meal on growth performance,nitrogen excretion,and immune index of juvenile Takifugu rubripesIn this experiment were studied using juvenile tiger puffers with an average initial body weight of 14.96 g.The experimental diets contained two control groups with no fish protein hydrolysate,positive control group(PC)containing 40%fish meal,negative control group(NC)containing 28%fish meal.For the other two groups,5.2%(FPH-5.2)and 10.4%(FPH-10.4)hydrolyzed fish protein were added to the NC diet to replace 6%and 12%fish meal respectively.All the four experimental diets were isonitrogenous and isolipidic.The feeding trial was conducted in an indoor flow-through system.Each diet was fed to triplicate tanks for 8 weeks.The results showed that,the weight gain of the PC group was significantly higher than that of the NC group(P<0.05),whereas no significant difference was observed among PC,FPH-5.2,and FPH-10.4,or among NC,FPH-5.2,and FPH-10.4(P>0.05).After 3hours of static-water feeding,the concentration of ammonia nitrogen in the rearing water in the PC group was significantly higher than that in the NC group and the FPH-5.2 group(P<0.05),but not significantly different from that in the FPH-10.4group(P<0.05);the FPH-10.4 group was significantly higher compared to the FPH-5.2 group(P<0.05),but not significantly different from the NC group;there was no significant difference between the FPH-5.2 group and the NC group(P>0.05).The content of serum complement protein C3 in the NC group was significantly lower than those in other groups(P<0.05).The content of serum complement protein C4 in the NC group and FPH-5.2 group was significantly higher than that in the FPH-10.4and PC groups(P<0.05).The level of serum immunoglobulin M in the FPH-10.4group was significantly higher than that in the NC group(P<0.05).The results showed that supplementation of a certain level of fish protein hydrolysate in the diet replacing fish meal had growth-promoting effect,while high level of fish meal had a significant growth-promoting effect,but the high level of dietary fish meal would cause the increase of ammonia nitrogen excretion in the rearing water.Supplementation of a certain level of fish protein hydrolysate(5.2%)could reduce the ammonia nitrogen excretion in the rearing water.Supplementation of a certain level of fish protein hydrolysate(10.4%)in the diet replacing fish meal can improve the immunity of fish to some extent.