Energy partitioning into growth, respiration, excretion and exuvia during larval development of the shrimp Farfantepenaeus paulensis

Energy channeled into growth (P), metabolism maintenance (R), excretion (E) and exuvia (E(v)) were quantified in feeding larval stages of Farfantepenaeus paulensis reared under commercial practices at 26 +/- 1 degrees C and 34 +/- 1 per thousand S. Dry weight, oxygen consumption, ammonia-N excretion and energy content were determined in protozoeal (PZ I-PZ III) and mysid (M I-M III) stages. In stages PZ III and M I, a higher weight increment (P) was observed compared to other larval stages. Energy expended in metabolism (R) increased through each subsequent stage, showing higher increment in the intervals PZ II-PZ III (1.7-fold) and PZ III-M I (1.8-fold). Losses by excretion (E) and exuvia (E(v)) presented lower values compared to P and R. From the total energy assimilated between PZ I and M III, growth comprised 42% while metabolism 52%. The percentage of assimilated energy channeled into growth (net growth efficiency or K2) was approximately 50% in PZ I and PZ II, reaching the highest value in PZ III (K2 = 69.9%). In the following stages, K2 remained between 33.3% and 49.8%. The metabolism (R) and growth (P) ratio showed higher growth investment in PZ III (R/P = 44.9%) compared to other stages. PZ I and PZ III exhibited higher growth in relation to individual energy content (P/B > 100%), while M II and M III presented lower results (P/B = 12.8-18.6%). Energetics of larval development indicated a planktonic phase with intense swimming activity and high metabolic rate, ingestion and growth (PZ I-PZ III). The transition to a benthic existence was marked by decreased metabolic rate and growth (M I-M III). These energetic parameters may be used as condition indices for cultured larvae as they help to explain how hatchery practices may affect metabolism and growth of the organisms.