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.