Physiological, nutritional,
and immunological role of dietary β1-3
glucan and ascorbic acid 2-monophosphate in Litopenaeus vannamei
juveniles
N.
López, G. Cuzon, G. Gaxiola, G. Taboada, M. Valenzuela, C. Pascual, A. Sánchez,
C. Rosas-2003
Aquaculture, 224(1-4): 223-243
Abstract :
The present study was designed to determine the
effect of dietary β1-3 glucan (BG) and a megadose of vitamin C on the
nutrition (growth and survival, blood glucose, lactate, acylglycerides,
cholesterol, hemocyanin [Hc], digestive gland glycogen [DGG]) and the
immunological system (blood cells, prophenoloxidase [ProPO]) in Litopenaeus
vannamei juveniles. Each treatment was replicated five times.
Nutritional condition and immunological response of shrimp were recorded
after 40 days of feeding with specific diets and during 48 h after a
salinity shock (35–0 ppt). A significantly greater growth rate was
observed in shrimp fed with BG or vitamin C diets than in the control group.
Higher blood protein, total blood cells, granular cells, and ProPO activity
were recorded in shrimp fed with vitamin C as compared to the remaining
treatments. That means that BG was degraded in the digestive gland by β-glucanases
to produce energy, permitting the use of more proteins for growth, whereas
vitamin C was used to improve animal health, enhancing general metabolism in
shrimp. The salinity stress induced a rapid use of reserves,
triacylglycerols (TAGs), and cholesterol were reduced in blood and probably
used as a source of energy or synthesis in the digestive gland. The increase
in digestive gland glycogen 24 h after the salinity shock evidenced the use
of these reserves by shrimp fed with all diets. In general, after the
salinity, shock blood cells increased in shrimp fed with glucans and
decreased in shrimp fed with vitamin C, whereas ProPO decreased in all
shrimp after the salinity shock. This could mean that after the salinity,
shock shrimp fed with glucans could synthesize cells and ProPO, whereas in
shrimp fed with vitamin C, blood cells were just used to respond to the
stress. After the salinity shock, an increment in the ProPO/granular cell
ratio was observed in shrimp fed with vitamin C, indicating that these
shrimp could rapidly increase the components of their immune system. In
contrast, a continuous reduction in ProPO/granular cell ratio was observed
in shrimp fed with glucans, revealing that with this type of
immunostimulant, shrimp drive their immunological equipment to respond
continuously to the stress. These results could explain why shrimp fed with
immunostimulants presents immunological fatigue in contrast to shrimp fed
with additives that improve their nutritional status, like vitamin C.
(Universidad Centroamericana, Managua, Nicaragua,
e-mail of C. Rosas: crv@hp.fciencias.unam.mx)