Response of juvenile Litopenaeus vannamei to varying levels of calcium phosphate monobasic supplemented to a practical diet

An 8-week growth trial was conducted to investigate phosphorus utilization of juvenile Litopenaeus vannamei reared in natural seawater. Six test diets (D1, D2, D3, D4, D5, D6) were formulated by gradually adding calcium phosphate monobasic into the basal diet (D1) at the level of 0.57%, in which the content of phosphorus in diets D1, D2, D3, D4, D5, D6 were 0.91%, 1.05%, 1.18%, 1.33%, 1.48%, and 1.63%, respectively. Thirty shrimp with average initial body weight of 0.16 g were randomly stocked into each tank and reared in a static-seawater system. Each diet was fed to three replicate tanks of shrimp. Shrimp were fed to apparent satiation. Percent survival ranged from 95.6% to 100% and no significant differences were observed among treatments (P > 0.05). Weight gain increased and feed conversion ratio decreased with the increase of dietary calcium phosphate monobasic and significant differences were observed when dietary total phosphorus content reached 1.33% (P < 0.05). The content of whole body ash, calcium and phosphorus also increased with the increase of dietary calcium phosphate monobasic and significant differences were observed when dietary total phosphorus reached 1.63% and 1.18%, respectively. However, the body calcium/phosphorus ratio decreased and significantly differences were observed when dietary total phosphorus and calcium phosphate monobasic reached 1.18% and 1.47:1, respectively. Significant increases of exoskeleton ash, calcium and phosphorus contents were observed when dietary total phosphorus increased to 1.18%, 1.33% and 1.05%, respectively; however, no significant differences were observed in carapace calcium/phosphorus ratio. The results suggest that the proper total dietary P level and calcium phosphate monobasic supplementation for juvenile L. vannamei fed practical feed is above 1.33% and 1.7%, respectively, according to weight gain and feed conversion ratio under the conditions of this study.