Dietary supplementation with
arachidonic acid alters the stress response of gilthead seabream (Sparus
aurata) larvae
R.D.
Van Anholt, W.M. Koven, S. Lutzky, S.E. Wendelaar Bonga-2004
Aquaculture, 238: 369-383
Abstract:
Gilthead seabream (Sparus aurata L.) larvae
were fed Artemia nauplii enriched with a low or high level of
arachidonic acid (ArA, 20:4n-6; 1.5 and 7.5 mg ArA/g dw, respectively) and
their response to two stressors was determined. Larvae of 28 and 50 days
post-hatch (DPH) were subjected to 90 s of air exposure, where the remaining
28 DPH fish were fed for another 4 days and exposed to a decrease from 42‰
ambient salinity to 25‰ over 1 h. After feeding on the ArA-enriched Artemia,
the larvae of both age groups exhibited elevated ArA levels, decreased EPA
levels and decreased EPA/ArA and DHA/ArA ratios. At 32 DPH, the high ArA
larvae demonstrated better growth than cohorts fed the lower ArA diet, but
this effect did not occur in the 50 DPH larvae. Feeding the high ArA Artemia
strongly reduced the cortisol response after air exposure of both 28 and 50
DPH larvae. The low ArA larvae responded to the salinity decrease with an
initial increase in cortisol followed by a gradual decline below basal
levels, whereas the high ArA larvae responded with a drop followed by a
return to basal levels. After the onset of the salinity decrease the
whole-body Na+, K+-ATPase activity increased in larvae
of both dietary treatments. After 24 h, the ATPase activity had decreased in
the low ArA larvae, but remained elevated in the high ArA larvae, coinciding
with the osmoregulatory role of cortisol. Together with the salinity
decrease, the whole-body sodium content dropped in the high ArA larvae,
while no marked change occurred in the low ArA larvae. ArA appears to be
involved in the regulation of cortisol synthesis in a divergent way: dietary
supplementation with ArA down-regulated the cortisol response after air
exposure, while it up-regulated basal cortisol synthesis after salinity
change and enhanced the osmoregulatory balance accordingly.
(Department of Animal Ecology and Ecophysiology,
Faculty of Science, University of Nijmegen, Toernooiveld 1, Nijmegen 6525
ED, The Netherlands, e-mail: rvanholt@sci.kun.nl)