Pierrette Lemaire

Effect of probiotic Pediococcus acidilactici on antioxidant defences and oxidative stress of Litopenaeus stylirostris under Vibrio nigripulchritudo challenge

Antioxidant defences and induced oxidative stress tissue damage of the blue shrimp Litopenaeus stylirostris, under challenge with Vibrio nigripulchritudo, were investigated for a 72-h period. For this purpose, L. stylirostris were first infected by immersion with pathogenic V. nigripulchritudo strain SFn1 and then antioxidant defences: superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (Gpx), Total antioxidant status (TAS), glutathiones and induced tissue damage (MDA and carbonyl proteins) were determined in the digestive gland at 0, 12, 24, 48 and 72 h post-infection (h.p.i.). In the meantime, TAS was also measured in the blood. Infection level of the shrimps during the challenge was followed by determining V. nigripulchritudo prevalence and load in the haemolymph of the shrimps. Changes in all these parameters during the 72-h.p.i. period were recorded for control shrimps and shrimps previously fed for one month with probiotic Pediococcus acidilactici MA18/5M at 10(7) CFU g(-1) of feed. Our results showed that immersion with V. nigripulchritudo led to maximal infection level in the haemolymph at 24 h.p.i. preceding the mortality peak recorded at 48 h.p.i. Significant decreases in the antioxidant defences were detected from 24 h.p.i. and beyond that time infection leaded to increases in oxidative stress level and tissue damage. Compared to control group, shrimps fed the probiotic diet showed lower infection (20% instead of 45% at 24 h.p.i. in the control group) and mortality (25% instead of 41.7% in the control group) levels. Moreover, infected shrimp fed the probiotic compared to uninfected control shrimps exhibited very similar antioxidant status and oxidative stress level. Compared to the infected control group, shrimps fed the probiotic sustained higher antioxidant defences and lower oxidative stress level. This study shows that bacterial infection leads to oxidative stress in L. stylirostris and highlighted a beneficial effect of P. acidilactici, suggesting both a competitive exclusion effect leading to a reduction of the infection level and/or an enhancement of the antioxidant status of the shrimps.

Osmoregulatory capacity according to nutritional status, molt stage and body weight in Penaeus stylirostris

Abstract Hypo-osmoregulatory capacity (or hypo-OC, i.e., the difference between the osmolality of the haemolymph and that of sea water), haemolymph glycemia and haemolymph sodium and chloride concentrations of Penaeus stylirostris were studied in experimental tanks according to the size, the molt stage and the nutritional status of the shrimp. Osmolality and haemolymph glycemia of fed and starved P. stylirostris were also studied in earthen ponds in fluctuating sea water according to time. In experimental tanks, the absolute hypo-OC of shrimp decreased linearly with increasing wet weight for each molt stage considered. For specimens weighing 16.6±1.7 g, the absolute hypo-OC was maximum in stage C (217±17 mosm kg −1 ) and significantly lower in stages B (165±16 mosm kg −1 ), D 0 (181±18 mosm kg −1 ), D 1 (146±20 mosm kg −1 ) and D 2 (135±13 mosm kg −1 ). The hypo-OC and haemolymph glucose concentration varied significantly after the food supply. No variations in haemolymph sodium and chloride concentrations were observed. In earthen ponds, haemolymph osmolality and haemolymph glucose concentration of molt stage C shrimp increased shortly after the food supply. When shrimp were kept starved for 24 and 48 h, haemolymph osmolality remained constant and haemolymph glucose concentration varied only slightly according to time. In light of these results, the use of shrimp hypo-OC (and/or haemolymph osmolality) and haemolymph glycemia in aquaculture as potential physiological indicators of disturbance in the aquatic environment is discussed.

Combined effect of temperature and salinity on osmoregulation of juvenile and subadult Penaeus stylirostris

In New Caledonia, the “syndrome 93,” which results in mass mortalities of farmed shrimp Penaeus stylirostris, occurs during the transitional and the cold seasons. The transitional season is characterized by an important fall in the average water temperature from 28 to 19 °C in 2 weeks. Besides this marked temperature fall, there are also nyctemeral temperature changes of up to 7 °C in 12 h. The cold season is characterized by an average water temperature of 19 °C with extreme lows of 14 °C. The objective of this study was to determine the effect of temperature and its variations on the osmoregulatory capacity of juvenile (7–10 g average weight) and subadult (25 g average weight) shrimps subjected to conditions of different salinity. A reduction in temperature level resulted in a decreased osmoregulatory capacity (OC) (defined as the difference between the osmolality of the haemolymph and that of sea water) at low salinity (hyper-CO) and at high salinity (hypo-CO), respectively, below and above the isoosmotic point (26.2 ppt). In subadult shrimps, the hyper-CO was affected when temperature dropped from 26 to 22 °C. The hypo-CO was modified only when temperature decreased down to 15 °C. Furthermore, the sensitiveness of osmoregulation to temperature changes was dependent on the developmental stage of the shrimp. Subadults were more sensitive than juvenile animals. The value of the isoosmotic point, which did not depend on the shrimp developmental stage, increased when temperature decreased to 17 or 15 °C. Our results provide an additional explanation of the “syndrome 93” and display the unfavourable influence of marked temperature drop on shrimp health. Our research could provide a possibility of seeking a nutritional and/or genetic solution to improve the capacity of the shrimps to maintain their homeostasis within a rearing medium with fluctuating temperatures.