At the end of the 56-day feeding trial, 150 shrimp from the five
treatment groups were counted and weighed. Each treatment was
conducted with 30 shrimp. The challenge test was conducted in
triplicate by an injection of 20 ml of a bacterial suspension resulting
in 2 105 CFU shrimp 1 into the ventral sinus of the cephalothorax
for the four challenge groups excluding the blank control group,
which received saline (20 ml) instead. Experimental shrimp (10
shrimp aquarium 1 ) were kept in 60-L glass aquaria containing
40 L of water at 28 1 C. Water was renewed daily in the period of
the challenge test.