Effects of heat-killed Lactobacillus plantarum supplemental diets on growth performance, stress resistance and immune response of juvenile kuruma shrimp Marsupenaeus japonicus Bate

The present study was conducted to determine effects of heat-killed Lactobacillus plantarum (HK-LP) on juvenile kuruma shrimp Marsupenaeus japonicus. A feeding trial was conducted with five dietary levels of a preparation containing 20% HK-LP (HK-LP Prep), 0 (control), 1, 10, 100 and 1000 mg/kg diet, and the test diets were fed to shrimp juveniles (initial weight about 4.9 g) for 60 days. After termination of a feeding trial, seven shrimps were selected randomly and fed the same test diets to monitor concentration of phosphorus and nitrate in rearing water, microbial community in rearing water and feces excreted from shrimp. Tolerance to salinity stress and immune response were measured 7 h after a low salinity exposure (from 35 ppt to 0 ppt). The results showed that the shrimp received HK-LP Prep at 100 and 1000 mg/kg diet significantly grew faster than control group (P0.05). Significantly better feed efficiency was also found at 1000 mg/kg compared to that in control. However, there were no significant differences in survival, feed intake, phosphorus and nitrate excretion, and bacteria count in both rearing water and feces. The cumulative mortality index to the low salinity stress test at 100 and 1000 mg/kg level was significantly lower than that in control group. In general, total haemocyte count, viable cell and rate of phagocytic activity decreased in all shrimp groups after the low salinity shock, but those parameters received HK-LP Prep at 100 and 1000 mg/kg were significantly higher than other groups. This study demonstrated that HK-LP enhanced the non-specific immune defense system of kuruma shrimp, providing them with higher resistance to the stress and better immune response. The application of oral HK-LP is one of the environmental friendly approaches for sustainable shrimp culture compared to the use of antibiotics and chemicals.