Modulation of stress response and productive performance of Litopenaeus vannamei through diet

The high tolerance of Litopenaeus vannamei to a wide range of salinity (1–50 psu) makes this species an excellent candidate for culture under low salinity, decreasing shrimp epidemics and water pollution in some coastal areas. However, salinity levels outside the optimal range could impose several physiological constraints that would in turn affect growth and survival, particularly in the presence of additional stressors (e.g. high densities, handling practices, and hypoxia). Despite shrimp susceptibility to individual stressors has been widely addressed, information regarding response to chronic and acute stressors combined and its relation to diet is scarce. Thus, the aim of our study was to determine the effect of diet on the susceptibility to chronic (low salinity) and acute (hypoxia and escape response) stressors in terms of culture performance and physiological indicators. We evaluated overall performance during culture of L. vannamei at low salinity (6 psu), fed with an experimental diet with low protein and high carbohydrate content (26% protein and 6% fish meal plus probiotic mixture) and compared to a commercial formula with high protein and low carbohydrate content (40% crude protein and 20% fish meal without probiotic mixture). At the end of the rearing experiment, shrimp were exposed to two types of acute stress, hypoxia and escape. Biochemical (hemocyanin, total proteins, glucose, and lactate) and bioenergetic (adenylic energy charge and arginine phosphate levels) variables were measured to assess chronic stress response (salinity) and acute stress response (hypoxia or escape). The experimental diet resulted in higher muscle energy status that was not affected by low salinity, although lipid levels were lower under this condition. This diet partially counteracted the low performance at low salinity and promoted greater protein efficiency. Hypoxia induced strong hyperglycemic and lactate increase as response, whereas escape response was characterized by a depletion of arginine phosphate levels, with a stronger decrease in shrimp fed experimental diet, due to the high initial level of this reserve. Some data (glucose levels in hemolymph and lipids in hepatopancreas) suggest that shrimp under chronic stress conditions (low salinity and high densities) present a low ability to respond to subsequent acute stressors such as hypoxia or escape. This work indicates that diet can increase the energy status of shrimp, enabling them to overcome potential multifactorial stressors, which are common in farming systems

Sperm quality in relation to age and weight of white shrimp Litopenaeus vannamei

Optimal sperm quality is an important feature for management of shrimp broodstock. The understanding of the sperm quality in relation to age and weight of shrimp is useful to select male broodstock. To evaluate the effect of age and weight on sperm quality, Litopenaeus vannamei males from the same cohort at ages of 6, 8, 10, and 12 months were examined, using body weight as a covariable in ANCOVA. Additionally, males of the same cohort at an age of 12 months, but from different culture conditions, were compared. Spermatophore weight, sperm count, and percentage of normal sperm were positively correlated to body weight. Sperm count was positively correlated to spermatophore weight and percentage of normal sperm. Males at an age of 12 months had superior sperm quality than younger males, based on observations of larger spermatophore weight, higher sperm count, and higher percentage of normal sperm. By eliminating the influence of body weight with the use of ANCOVA, the same effect was still observed, indicating that the effect of age of males on sperm quality was independent of body weight. However, when large differences in growth were forced by changing culture conditions, sperm quality differences were observed and could be explained by body weight. In conclusion, using 12-month-old males would lead to improved shrimp seed production, since they are mature males with high sperm quality. In addition, for improved productivity, it is important to consider the culture conditions under which domesticated male broodstock will be obtained. (C) 2003 Elsevier Science B.V. All rights reserved

Sperm Quality in Relation to Age and Weight of White Shirimp Litopenaeus Vannamei

Optimal sperm quality is an important feature for management of shrimp broodstock. The understanding of the sperm quality in relation to age and weight of shrimp is useful to select male broodstock. To evaluate the effect of age and weight on sperm quality, Litopenaeus vannamei males from the same cohort at ages of 6, 8, 10, and 12 months were examined, using body weight as a covariable in ANCOVA. Additionally, males of the same cohort at an age of 12 months, but from different culture conditions, were compared. Spermatophore weight, sperm count, and percentage of normal sperm were positively correlated to body weight. Sperm count was positively correlated to spermatophore weight and percentage of normal sperm. Males at an age of 12 months had superior sperm quality than younger males, based on observations of larger spermatophore weight, higher sperm count, and higher percentage of normal sperm. By eliminating the influence of body weight with the use of ANCOVA, the same effect was still observed, indicating that the effect of age of males on sperm quality was independent of body weight. However, when large differences in growth were forced by changing culture conditions, sperm quality differences were observed and could be explained by body weight. In conclusion, using 12-month-old males would lead to improved shrimp seed production, since they are mature males with high sperm quality. In addition, for improved productivity, it is important to consider the culture conditions under which domesticated male broodstock will be obtained

Gonadal development in male and female domesticated whiteleg shrimp Litopenaeus vannamei in relation to age, weight and grow-out conditions

Cultivation of whiteleg shrimp (Litopenaeus vannamei) is now entirely based on closed life-cycle populations, yet few studies have analyzed gonadal development in domesticated shrimp during grow-out in ponds. To determine the effect of age and weight on morphometric, histological, and biochemical variables associated with male and female gonadal development, shrimp from the same cohort, at ages of 6, 8, 10, and 12 months were examined using body weight as a covariable in an ANCOVA design. An additional comparison between two grow-out conditions in 1-year-old shrimp was done to separate the effect of size as a result of initial stocking densities. Age-related growth of gonads was clearly dependent on somatic growth for females but not for males, although differential somatic growth produced by stocking densities explained differences in growth of gonads for both sexes. Increase in oocyte diameter and differentiation associated with age and grow-out condition were independent of body weight. Age-related female gonadal development was accompanied by increases in lipid and protein concentrations, independent of body weight. Maturation of male reproductive organs (testicle, vas deferens, terminal ampoule, and spermatophore) was sequential and depended mainly on age, although body weight could explain differences caused by different grow-out conditions. An age-related decrease in concentration of lactate occurred in all male reproductive organs and could indicate a metabolic adjustment of sperm anaerobic metabolism and lactate clearance associated with gonadal development. We highly recommend waiting for optimal reproductive potential of females at 12 months to enhance spawning frequency and larval quality. At this age, body weight seems to be of secondary importance, although optimal conditions of cultivation are necessary to have adequate growth and balanced nutrition