O:N ratio as index of metabolic substrate changed in shrimp from all treatments as
postlarvae increased in age, showing a transition in the use of proteins as an energy
source in the first stages to a protein–lipid mixture in later stages. Minello and
Zimmerman (1991) reported that L. setiferus is the most herbivorous shrimp in the Gulf
of Mexico, which could explain its ability to use lipid–protein as a source of dietary
energy. As Taboada et al. (1998) stated, this could represent an advantage to L. setiferus
because these animals would be able to use low-cost energy sources for their metabolic
processes and exploit proteins as a structural component for growth. In a previous study,
Rosas et al. (1995) showed that the O:N ratio in L. setiferus PL changed according to 30
the protein level of the diet, with low values in shrimp fed on low or excess protein
levels, and high values in shrimp fed with an optimum protein level. These results
showed the wide ability of this species to use different metabolic substrates as energy
sources according to their availability.