The objective of this study was to confirm the growth response, immune response, histopathology, and the expression of White Feces Disease (WFD, also termed White Feces Syndrome or WFS) in Pacific whiteleg shrimp (L. vannamei) fed diets containing different inclusions of soybean meal (SBM) at 0%, 15%, 30%, and 30% SBM supplemented with enzyme or health solutions.
A series of feed trials was designed to verify that SBM, even at high inclusions in L. vannamei formulation, has no linkage with WFD. Two trials were conducted, one in a closed clearwater tank system at Kasetsart University, Thailand and one in a pond-based hapa system at a commercial shrimp farm in Chachoengsao province, Thailand. SPF-certified shrimp postlarvae, PL12, were obtained from a local hatchery and transferred to the testing facilities.
In the first trial, SPF-PL12 were acclimated for 12 days in a common tank and shrimp (0.003g) were then stocked at a density of 120 PL/m2 or 80 shrimp/tank using four replicates under laboratory conditions. The shrimp were fed four times daily at a satiation rate. At the end of the 45-day feeding period, overall growth performance associated with different SBM inclusions was monitored. Harvest samples have an average weight of 3.28 g. Additionally, the immune responses and WFD related conditions such as Vibrio counts, EHP infection, and histology of the hepatopancreas, including Aggregated Transformed Microvilli (ATM) were determined. Furthermore, the effect of different SBM inclusion after a stress test with low dissolved oxygen (1.5-2mg/l) and a challenge test with Vibrio parahaemolyticus AHPND strain were examined. Finally, the nutrient digestibility of each dietary treatment was also analyzed.
In the second trial, SPF-PL12 were stocked in nursery tanks for 30 days at a stocking density of 1,250 PL/m2. The shrimp (4.4g) were then stocked at a density of 1,320 shrimp/hapa or 110 shrimp/m2 using four replicates under pond-based hapa conditions. The shrimp were fed four times daily at a satiation rate following the Cooperator's standard feeding guide. Sampling was carried out on a biweekly basis. At the end of the 66-day feeding period, overall growth performance, immune and health parameters associated with different dietary treatments were monitored. Harvest samples have an average weight of 20.1 g. Shrimp fed different SBM inclusions showed similar growth rates in both laboratory and field trials.