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

Abstract

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.