The ventral muscle in the 6th abdominal segment under the intestine is one of the largest in the post larvae shrimp. The ratio between the width of this muscles and the width of the gut has already been proposed and used in PL quality control (Muscle Gut Ratio of 4:1 based on comparisons with wild post larvae). However, in practice, it was found that this measurement can be difficult due to the movement of the shrimp on the slide. Killing the PL also led to post mortem changes which did not reflect the true condition of the muscle. To overcome this, we use a 50% criterion. If the muscle constitutes less then 50% of the width of the tail at the midpoint of the 6th abdominal segment the quality is unacceptable. More than 50% is acceptable.