The effect of dissolved oxygen and salinity on oxygen consumption, ammoniaexcretion and osmotic pressure of Penaeus setiferus (Linnaeus) juveniles

The white shrimp Penaeus setiferus (Linnaeus) is an abundant species in the coastal lagoons and estuaries of the Gulf of Mexico. This species is well adapted to environments of low salinity and can tolerate low levels of diss olved oxygen. This study was designed to measure the effects of prolonged h ypoxia and salinity level on: (a) the oxygen consumption and ammonia excret ion, (b) the metabolic substrate (O:N) on fasting (24 h) and feeding animal s, (c) the osmotic pressure of the hemolymph and, (d) the body water conten t of P. setiferus juveniles. The shrimp were exposed to different levels of dissolved oxygen (DO of 2, 3, 4 and 5.8 mg 1(-1)) and two salinities (15 a nd 35 parts per thousand) for a period of 60 days. Results indicate that th ese animals are oxyregulators between 5.8 and 4 mg 1(-1) DO and oxygen conf ormers between 3 and 2 mg 1(-1) DO in both salinities. There was not a sign ificant effect of salinity on the oxygen consumption in either nutritional condition. Ammonia excretion was significantly greater in 15 parts per thou sand than in 35 parts per thousand. In 15 parts per thousand the ammonia ex cretion diminished as a function of the DO. In unfed animals the ammonia ex cretion diminished in a direct proportion to the decrease of the DO, while in fed animals they were ammonia-regulators between 5.8 and 4 mg 1(-1) DO. In 35 parts per thousand the ammonia excretion increased in the fed animals exposed to 2 and 3 mg 1(-1) DO. In low salinity the animals fundamentally maintained proteins as their energy substrate at all levels of DO, while in the case of 35 parts per thousand of salinity the shrimp changed the metab olic substrate from lipids-proteins (5.8 and 4 mg 1(-1) DO) to proteins (3 and 2 mg 1(-1) DO). These results show that P. setiferus juveniles are capa ble of changing their energy substrate in response to salinity and DO chang es, This fact may be related to a possible strategy that allows them to obt ain energy from proteins. The stability of osmotic pressure between 35 and 5 parts per thousand and the changes which have been observed in the total content of water give rise to the supposition that the pool of free amino a cids, whether of muscular or nutritional origin, are the key to this strate gy. (C) 1999 Elsevier Science B.V. All rights reserved.