Introduction
This study aims to assess the influence of shelter placement and undernutrition on physiological stress and predation in Penaeus vannamei. In this species of major aquaculture interest, environmental and nutritional conditions strongly modulate the behavior, physiology and resistance to external aggressions. The main hypothesis is that the presence of shelter could improve the welfare and reduce the risk of predation, while undernutrition is likely to increase vulnerability by weakening energy reserves and shrimp ability to cope with stress. So, a higher oxygen consumption, a peak in blood sugar and a lower survival rate in shrimp with undernourished and homeless conditions compared to shrimp with more shelter and feeding would be studied.
Material and Methods
24 tanks were prepared in the same recirculated water system. 4 treatments were randomly applied (ie 6 replications per treatment) to the different tanks for 21 days (Table 1).
Table 1: Summary of experimental conditions
Shelter
Overnutrition (9% of the tank biomass)
Undernutrition (4.5% of the tank biomass)
Presence
10 shrimp of 0.8g minimum
10 shrimp of 1g minimum
Lack
10 shrimp of 0.8g minimum
10 shrimp of 1g minimum
Shrimp were fed twice daily in accordance with their feeding condition. Water physico-chemical parameters (pH, Nitrite, Salinity, Temperature) were monitored twice a week throughout the experiment.
The physiological stress parameters measured were:
Oxygen consumption,
Hemolymph glucose level,
Survival rate.
Results and Discussion
The first average results observed are presented in Table 2.
Table 2 : First average results
Feeding condition
Shelter
Oxygen consumption (mgO2 g-1 h-1)
Hemolymph glucose level (mg dL-1)
Survival rate (%)
Specific growth rate (% day-1)
Overnutrition
Lack
0.80 ± 0.13
59.58 ± 19.69
56.67 ± 10.33
3.27 ± 0.71
Overnutrition
Presence
0.82 ± 0.15
55.17 ± 20.95
58.33 ± 11.69
3.47 ± 0.65
Undernutrition
Lack
0.95 ± 0.18
32.00 ± 8.51
60.00 ± 16.73
1.51 ± 0.86
Undernutrition
Presence
0.87 ± 0.14
33.57 ± 11.01
70.00 ± 8.94
2.15 ± 0.48
Lower oxygen consumption and a best survival rate in shrimp with shelter compared to homeless shrimps may show that the presence of refuges reduces stress and predation in P. vannamei.
A higher glucose concentration in the hemolymph, along with an increased specific growth rate in overfed shrimp, may indicate that while overfeeding promotes growth, it could be detrimental to their overall health.
These results provide a better understanding of how habitat structure and nutritional status interact to determine juvenile survival.
In perspective, this work could provide useful recommendations for the breeding and growth of P. vannamei, by combining enrichment of the environment and food management to improve welfare, robustness and survival.