Environmental Engineering Reference
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after being conditioned on diet containing either maintenance or optimal dietary protein
levels Pascual et al
.
,( 2006). Juvenile shrimp were fed for 21 days on diets containing 5% and
40% dietary protein. Hemolymph metabolites (glucose, cholesterol, protein, acylglycerols,
and lactate), hemocyanin, osmoregulatory capacity, digestive gland glycogen and lipids,
and immune conditions (hemocytes concentration, phenoloxidase activity, respiratory burst:
basal and activated) were evaluated and considered as initial condition. After that time,
shrimp were starved for 21 days. A reduction in all physiological and immunological
indicators was observed with starvation. The results demonstrate that shrimp are well
adapted to tolerate food deprivation for some time but that this tolerance is closely related
to its previous nutritional condition. In the case of shrimp fed 40% DPL, wet weight,
nutritional and immune condition was significantly affected after 14 days of starvation. In
shrimp previously fed 5% DP, tolerance to starving condition was limited to only a few days
(7 days) as a result of low reserves of circulatory and mussel proteins. All these results
demonstrate that dietary protein levels can governor the immune condition of shrimp
through the management reserves metabolism.
Domestication is other important aspect to obtain better results during culture; however,
artificial selection has important implication on physiological adaptations. Pascual et al.,
(2004) studied wild and seventh-generation cultivated shrimp to determine how size-based
selection could alter the nutritional and immunological conditions of
Litopenaeus vannamei
.
Wild juveniles and a sample of seventh-generation cultured shrimp were acclimated under
identical conditions. During 55 days, shrimp were fed a high (HCHO: 44%) or a low (LCHO:
3%) carbohydrate diet. Wild shrimp showed a direct relation between dietary CHO and
lactate, protein and hemocyte levels indicating that dietary CHO was used for protein
synthesis via transamination pathways. In seventh-generation cultured shrimp these
parameters were inversely proportional to dietary CHO level, indicating the capacity to
synthesize protein from dietary CHO was repressed in cultured shrimp. Farmed shrimp
showed a limited capacity to respond to LCHO diets demonstrating high protein
dependence in their metabolism and immune response. These results demonstrate that
during size-based breeding programs other metabolic process than CHO catabolism can be
selected. The incapacity of shrimp to use dietary CHO could limit protein reduction of diets
and limit the efforts of the shrimp industry to be ecologically and environmentally
profitable.
Considering the results arising from a series of studies, Arena
et al
.
, (2003); Pascual
et al
.
, (2004
a and b), developed a conceptual model about how dietary components modulate the fate of
energy intake, the nutritional status and immune system of juvenile
L. vannamei
(Fig. 6). The
environment and genetic variability are the basis of the model, since as mentioned; the
interaction between these elements affects the digestive capacity, the flow of energy, protein
synthesis, osmoregulation, disease resistance and the degree homeostatic control.
Degradation of starch leads to glucose uptake, it is transported directly to the hemolymph
or metabolized through glycolysis (
GL
); subsequently pyruvate through acetyl-coenzyme-A
(
A-CoA
) can enter the Krebs cycle (
KC
) and continue with the respiratory chain (
RC
) to
obtain energy (
ATP
). The digestive capacity of wild shrimp revealed the importance of
taking advantage of dietary CHO, which can be associated with the various points of
metabolic regulation of the glycolytic pathway. Nine of the ten essential amino acids can be
synthesized from glucose, where glutamate provides the amino group. In the opposite
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