Influence of dietary protein levels on growth, digestibility, digestive enzyme activity and stress tolerance in white-leg shrimp, Litopenaeus vannamei (Boone, 1931), reared in high-density tank trials

The effects of dietary protein (DP) levels on the growth, digestibility, digestive enzyme activity and stress tolerance of Litopenaeus vannamei (Boone, 1931) were investigated in high-density (375 m(-3)) tank trials. Shrimps (6.2 +/- 0.2 g) were fed diets with five different protein levels (31%, 35%, 39%, 43% and 47%) for 60 days. The results showed that variations in DP significantly (P<0.05) influenced the growth performance, digestibility, enzyme activity and their ability to tolerate stress. Weight gain showed a linear increase in relation to crude protein (CP) up to 43% and showed a slight decrease with a further increase to 47%. Feed conversion ratio was observed to be the lowest in CP 43%: 2.53. A higher protein efficiency ratio was observed with the low-protein diet CP31 (1.07); however, it was not significantly different from the rest of the dietary treatments. Protein digestibility was the highest (75.71%) in CP47 and the lowest (71.94%) in CP31. Protease activity ranged between 63.7 and 70.2 (U Protein(-1)), and showed a positive correlation with the DP levels. Shrimp fed CP43 well tolerated a sudden decline in salinity and survived for 548.3 min in fresh water. Observations from this study indicate that a DP level around 43% could be optimum for L. vannamei in high-density culture systems in the absence of natural productivity.