Citrate synthase and pyruvate kinase activities during early life stages of the shrimp farfantepenaeus paulensis (crustacea, decapoda, penaeidae): effects of development and temperature

摘要

Energy metabolism in early life stages of the shrimp Farfantepenaeus paulensis subjected to temperature reduction (26 and 20 deg C) was determined using the activities of citrate synthase (CS) and pyruvate kinase (PK). At both temperatures, weight-specific activity of CS decreased throughout the ontogenetic development from protozoea II (PZ II) to postlarva XII-XIV (PL XII-XIV). PK activity reached a pronounced peak in PL V-VI, followed by a further decrease in PL XII-XIV. Temperature reduction produced variation in oxygen consumption rates (QO_2), ammonia-N excretion and in enzyme activities. Ammonia-N excretion was higher at 20 deg C in mysis III (M III), PL V-VI and PL XII-XIV, resulting in substantially lower O:N ratios in these stages. QO_2 was increased in protozoea II (PZ II) and mysis I (M I) at 26 deg C, while no difference in QO_2 was detected in the subsequent stages at either temperature. This fact coincided with higher CS and PK activities in M III, PL V-VI and PL XII-XIV at 20 deg C compared with 26 deg C. Regressions between individual enzyme activities and dry weight exhibited slope values of 0.85-0.92 for CS and 1.1-1.2 for PK and temperature reduction was reflected by higher slope values at 20 than at 26 deg C for both enzymes. Weight-specific CS activity was positively correlated with QO_2 at 20 and 26 deg C, and may thus be used as an indicator of aerobic metabolic rate throughout the early stages of F. paulensis. The variation in enzyme activities is discussed in relation to possible metabolic adaptations during specific ontogenetic events of the F. paulensis life cycle. Here, the catalytic efficiency of energy-metabolism enzymes was reflected in ontogenetic shifts in behaviour such as larval settlement and the adoption of a benthic existence in early postlarvae. In most cases, enhanced enzyme activities appeared to counteract negative effects of reduced temperature.