Influence of highly unsaturated fatty acids on the
responses of white shrimp (Litopenaeus vannamei) postlarvae to low
salinity
E.
Palacios, A. Bonilla, A. Pérez, I.S. Racotta, R. Civera-2004
Journal of Experimental Marine Biology and Ecology, 299(2): 201-215
Abstract:
Salinity
stress tests are commonly applied in shrimp hatcheries to estimate the
quality of postlarvae (PL) to be used during growout. Higher larval survival
during culture and to a salinity stress test in both fish and crustaceans
have been reported when specimens were offered a diet containing high levels
of highly unsaturated fatty acids (HUFA). However, it is not clear if
increased survival is a result of better overall physiological condition
resulting from the diet or a specific effect of HUFA on osmoregulatory
mechanisms. This study analyzed if HUFA-rich diets could modify the fatty
acid composition of membranes in gills, and if this change in composition
could affect the activity of the Na+/K+ ATPase pump
and carbonic anhydrase in relation to changes in salinity. One-day-old
postlarvae (PL1) pooled from different spawns were fed for 20 days with Artemia
sp. nauplii enriched with three levels of HUFA: low, medium and high. At
PL20, survivals during culture and to salinity stress test (tap water for 30
min) were evaluated. Also at this stage, Na+/K+-ATPase
and carbonic anhydrase activity, morphometric variables, and fatty acid
composition in the hepatopancreas and gills were measured after they were
submitted to a salinity challenge in dilute seawater (10 ppt) for 3 h. No
significant differences were observed in survival rates during culture, but
survival to a salinity stress test was higher and gill area was larger in
PL20 fed the Artemia sp. nauplii enriched with medium HUFA levels,
probably as a result of an increased 22:6n-3 content and higher
22:6n-3/20:5n-3 ratio in this diet and in the tissues of the organisms fed
this diet. Na+/K+-ATPase specific activity was
significantly higher in posterior gills, while the specific activity of the
carbonic anhydrase was higher in anterior gills. Enzymatic activities
increased significantly in PL20 submitted to a salinity challenge, and HUFA
levels in the diet affected both. The proportion of fatty acids in
hepatopancreas and gills were significantly affected not only by diet, but
also by exposure to dilute media. This effect is discussed in relation to an
increase in gill surface and changes in fatty acid composition in the
phospholipids present in gill membranes, which can modify the permeability
and the activity of the Na+/K+-ATPase pump. The
beneficial effect of HUFA supplementation in the diet on survival to
salinity stress test is partially related to modification of fatty acid
composition of gills and to a larger gill area, which in turn enhances
osmoregulatory mechanisms, namely Na+/K+-ATPase and
carbonic anhydrase activities.