A PHYSIOLOGICAL APPROACH TO THE STUDY OF GROWTH AND BIOENERGETICS IN THE FRESHWATER SHRIMP Macrobrachium rosenbergii

Oxygen consumption, ninhydrin‐positive nitrogen excretion and carbon dioxide production were monitored in juvenile Macrobrachium rosenbergii fed a series of experimental diets containing variable levels of protein, lipid and carbohydrate. Using respiratory quotient and nitrogen excretion data, metabolic substrate ratios and oxycalorific coefficients were derived for transformation of metabolic observations to a caloric basis. Energy partitioning and growth were evaluated for each dietary treatment by means of individual energy and nitrogen balances generated from physiological rate functions. Measurements of nitrogen excretion and corresponding metabolic substrate ratios indicate that the protein‐sparing effect of non‐protein energy sources is maximized at a lipid:carbohydrate ratio of 1:4. Analysis of energy and nitrogen budgets also confirms this relationship. Nitrogen retention in the experimental animals was found to be positively correlated with dietary protein with a slight decline and leveling off at 30% protein. In contrast, protein content operated in an inverse manner upon physiological energetics; maximum caloric growth occurred at lower protein level. Based on this inverse relationship, it is concluded that optimal conditions for growth are achieved with a 25% protein diet containing a lipid:carbohydrate ratio of 1:4.