PHOSPHORUS DIGESTIBILITY AND RETENTION IN FARMED SHRIMP Litopenaeus vannamei FED SELECTED INORGANIC FEED PHOSPHATES
The present research was conceived to respond the following question regarding shrimp phosphorus nutrition: What would be the best inorganic phosphate to be supplemented in diets for growth of juvenile shrimp (Litopenaeus vannamei)?
A control diet was formulated to be supposedly P-deficient and with no addition of inorganic phosphorus. To this control diet, t o increase the P-level from 4.4g/kg to around 6.9g/kg different phosphorus sources were added: Aliphos® DCP (DCP), Aliphos® Monocal (MCP) and Windmill® Aquaphos (MAP). The trial was performed in a recirculation system with 16 tanks of 500L to enable four repetitions per trial group. Tanks were stocked with 33 shrimp/replicate and fitted with settling columns. Salinity of the water was 34ppt, the average temperature 30oC. Feeds were supplied continuously via belt feeders . Shrimp were weighed at the start and end of the trial. Shrimp at the start and end of the trial were also sampled for whole body analysis to enable the calculation of ingredient retention. Faeces, for digestibility analysis, were collected six times daily from the settling columns.
Shrimp performance was very good in general, growth and feed conversion ratio (FCR) achieved values according practical conditions. Survival rates were lower for shrimp fed the control and MCP diets, whereas shrimp fed the control and DCP diets showed significantly lower growth and higher FCR. A persistent exuvia consumption was observed for shrimp fed
the control and DCP, decreasing for MCP and not apparent in the case of Aquaphos.
P hosphorus digestibility of the feed phosphates turned out to be negative for DCP increasing to 55% for MCP and 107% in the case of Aquaphos. Phosphorus retention efficacy was highly correlated with the P-digestibility of the different feed phosphates. It was the highest for Aquaphos with 52%, followed by MCP with 40.7% , but DCP having a negative retention of -0.9%. Part of the difference between P-digestibility and - retention seems to be contributed by leaching of P from the pellets.
These trial results confirm earlier trial findings , with Aquaphos having a higher P-bioavailability than in case of MCP and DCP.
