Roberto Brito

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

Abstract 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 dissolved oxygen. This study was designed to measure the effects of prolonged hypoxia and salinity level on: (a) the oxygen consumption and ammonia excretion, (b) the metabolic substrate (O:N) on fasting (24 h) and feeding animals, (c) the osmotic pressure of the hemolymph and, (d) the body water content of P. setiferus juveniles. The shrimp were exposed to different levels of dissolved oxygen (DO of 2, 3, 4 and 5.8 mg l −1 ) and two salinities (15 and 35‰) for a period of 60 days. Results indicate that these animals are oxyregulators between 5.8 and 4 mg l −1 DO and oxygen conformers between 3 and 2 mg l −1 DO in both salinities. There was not a significant effect of salinity on the oxygen consumption in either nutritional condition. Ammonia excretion was significantly greater in 15‰ than in 35‰. In 15‰ the ammonia excretion diminished as a function of the DO. In unfed animals the ammonia excretion 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 l −1 DO. In 35‰ the ammonia excretion increased in the fed animals exposed to 2 and 3 mg l −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‰ of salinity the shrimp changed the metabolic substrate from lipids-proteins (5.8 and 4 mg l −1 DO) to proteins (3 and 2 mg l −1 DO). These results show that P. setiferus juveniles are capable of changing their energy substrate in response to salinity and DO changes. This fact may be related to a possible strategy that allows them to obtain energy from proteins. The stability of osmotic pressure between 35 and 5‰ and the changes which have been observed in the total content of water give rise to the supposition that the pool of free amino acids, whether of muscular or nutritional origin, are the key to this strategy.

Effect of salinity in survival, growth, and osmotic capacity of early juveniles of Farfantepenaeus brasiliensis (decapoda : Penaeidae)

The effect of salinity in survival, growth and osmotic capacity of juvenile Farfantepenaeus brasiliensis was determined. Survival was not affected by salinities from 15 to 35‰ during 96 h exposure periods. Shrimps exposed to 5 and 10‰ were noticeably affected by salinity with a survival of 0 and 48% after 96 h, respectively. Lethal salinity for 50% of the individuals in 96 h (LS50, 96 h) at 28°C was 10‰. Growth rate (mg dw day −1) was significantly higher at higher salinities. The isosmotic point of early juvenile F. brasiliensis was 794 mOSm kg−1, at around 25‰. Results indicate that F. brasiliensis has low tolerance to low saline environments, and grows better in salinities greater than its isosmotic point. Osmotic capacity seemed to be related to biological characteristics that determine the environmental preferences and behavior, as well as the distribution of this shrimp species.

Growth, metabolic rate, and digestive enzyme activity in the white shrimp Litopenaeus setiferus early postlarvae fed different diets.

Growth rate, soluble-protein content, oxygen consumption, ammonia excretion, and digestive-enzyme activity were studied in Litopenaeus setiferus early postlarvae under four feeding regimens that included combinations of freshly hatched Artemia nauplii, microparticulate commercial diet, and algae. Growth and of postlarvae fed a mixed diet were significantly higher. Artificial diet used alone caused the lowest growth, lowest soluble-protein content, higher ammonia excretion, lowest O:N ratio, and higher proteolytic and amylase activities. The artificial diet stimulated proteolytic activity and ammonia excretion of postlarvae, apparently in response to some deficiency in protein composition of the diet. Based on results in growth, soluble-protein content, enzymatic activity, and metabolic substrate, we determined that partial substitution of Artemia nauplii by artificial diet, with or without addition of algae when rearing early postlarval stages, will benefit the growth and nutritional state of L. setiferus postlarvae.

Critical dissolved oxygen level to Penaeus setiferus and Penaeus schmitti postlarvae (PL10–18) exposed to salinity changes

Abstract Dissolved oxygen is the most important limiting factor in the intensive cultivation of shrimp species. The critical oxygen level and its effects upon the energy metabolism of postlarvae (PL 10–18 ) of Penaeus setiferus and Penaeus schmitti exposed to diverse salinities were estimated. In both species the critical oxygen level (COL; estimated as the point of inflection of the curve obtained from the relation between the oxygen consumption and the oxygen concentration) was affected by salinity concentration. In P. schmitti , the COL was 5 mg l −1 for salinities of 38, 30, 20 and 15%., and 4.5 mg l −1 for animals kept at 25%. salinity. In P. setiferus , the COL was 5.0 mg l −1 in 37, 30, 25, 20 and 10%. salinities and 4.5 mg l −1 in 15, 5 and 1%. salinities. The energy deficit (END; deficit of metabolic energy) caused by the metabolic oxygen critical concentration was in P. schmitti 13.9% (38%. salinity) and 26.3% (30%. salinity), with intermediate values of 17.2, 22.7 and 24.7% in 25, 20 and 15%. salinities, respectively. For P. setiferus , the END was between 9.1% (l%. salinity) and 25.1% (30%. salinity), with intermediate values for the remaining salinities. Based on these data, the optimum salinity for P. setiferus postlarvae was between 5%. and 15%., and was 25%. for P. schmitti postlarvae. At these salinities the tolerance for the decrease in the oxygen concentration was greater than in the rest of the salinities. The high COL obtained for the postlarvae of both species indicates that the culture conditions must be carefully maintained at this developmental stage to obtain the maximum metabolic performance of the shrimp.

The effect of eyestalk ablation on the energy balance of the pink shrimp, Penaeus notialis

Abstract 1. 1. The effect of eyestalk ablation on the energy balance of male and female pink shrimp Penaeus notialis adults was determined. 2. 2. The effect of ablation on ingested food, assimilation efficiency, assimiliation and oxygen consumption in both sexes was evident. It was reflected in the scope for growth obtained. 3. 3. The ablation of the eyestalks of females caused an increase in respiratory rate and a decrease in metabolic level with respect to intact shrimps. An increase in the respiratory rate could mean an increase in the physiologically useful energy (PUE). The effect of ablation in males produced an increase in the metabolic level without increase in the PUE. 4. 4. Although ablation caused an increase in the amount of ingested food, assimilated energy and the scope for growth in both sexes, it was less marked in males (39%) than in females (53%). 5. 5. These results suggest that the ablation does not increase the efficiency of the processes related to maturity in males as has been demonstrated for females of pink shrimp P. notialis . These differences may be related to the reproductive characteristics of males of P. notialis which is highly efficient and accelerated in normal conditions.