Growth, oxygen consumption, ammonia-N excretion, biochemical composition and energy content of Farfantepenaeus paulensis Pérez-Farfante (Crustacea, Decapoda, Penaeidae) early postlarvae in different salinities.

Physiological responses of early postlarval shrimp Farfantepenaeus paulensis to different salinities were evaluated. Growth, net growth efficiency (K(2)), oxygen consumption, ammonia-N excretion, protein, lipid, carbohydrate, ash and energy content were determined in postlarval stages PL VI-VII and PL XIII-XV at 5 per thousand, 15 per thousand, 25 per thousand and 34 per thousand. PL VI-VII and PL XIII-XV correspond, in the wild, to the penetration of postlarvae into estuarine zones and the adoption of benthic habits, respectively. Postlarvae were gradually acclimated to the various salinity levels in the stage PL VI-VII and were maintained there until reaching the stage PL XIII-XV. Although development time was not affected by salinity, growth was decreased at 34 per thousand. Oxygen consumption was less affected by salinity while ammonia-N excretion presented a negative correlation with salinity. In both stages, protein content was lower at 34 per thousand. In PL VI-VII, lipid was decreased at 5 per thousand, while no significant difference in lipid content was observed in PL XIII-XV. Carbohydrate and ash levels did not vary in function of salinity levels. Energy content was reduced in PL XIII-XV at 34 per thousand. Net growth efficiency (K(2)) between PL VI-VII and PL XIII-XV presented higher values at 15 per thousand and 25 per thousand, and the lowest at 34 per thousand. Enhanced energy expenditure due to osmoregulation was not detected as denoted by oxygen consumption rates. Nitrogen metabolism seems to play a key role in maintaining body fluids concentration in relation to medium salinity. It is concluded that the high degree of euryhalinity in these stages of F. paulensis may be an adaptation to ontogenetic events such as migration to estuarine areas. For aquaculture purposes, it is recommended to maintain these postlarval stages at salinities between 15 per thousand and 25 per thousand rather than 34 per thousand.