The effect of
dietary arachidonic acid (20:4n-6) on growth, survival and resistance to
handling stress in gilthead seabream (Sparus aurata) larvae
W. Koven, Y. Barr, S. Lutzky, I. Ben-Atia, R. Weiss,
M. Harel, P. Behrens, A. Tandler-2001
Aquaculture, 193 (1-2): 107-122
Abstract:
The effects of high dietary docosahexaenoic acid
(22:6n-3, DHA) and varying arachidonic acid (20:4n-6, AA) were tested on
growth, survival and resistance to handling stress in 5--35 day old gilthead
seabream larvae. Three enrichment treatments differing in their DHA/AA
ratios were fed to rotifers (Brachionus rotundiformis) and Artemia nauplii.
The high DHA (35.9% TFA) enrichment treatment (DHA-PL) contained no AA and
included lipid from the heterotrophically grown DHA-rich dinoflagellate
Crypthecodinium sp. A second enrichment treatment (AADHA), selected from an
earlier screening study, supplemented the high DHA enrichment treatment with
an AA-rich lipid (52% TFA) from the heterotrophically grown fungus
Mortierella alpina. A third enrichment treatment (ALGA) was the commercial
product Algamac 2000, which is devoid of AA, but includes approximately
12.9% of TFA as docosapentaenoic acid (DPA, 22:5n-6). Rotifers fed the
DHA-PL, AADHA and ALGA treatments demonstrated a range of DHA/AA ratios
(20.9, 5.6 and 10.1, respectively) as did the Artemia nauplii (25.8, 3.7 and
4.6, respectively).
The enriched rotifers were fed to larvae reared in
400 l V-tanks from day 5 to day 19 post-hatching. Following this period,
larvae were exposed to controlled handling stress during transfer to 27 l
aquaria, where they were then fed the enriched nauplii from day 20 to day 35
post-hatching. Although larval fatty acid profiles reflected the enrichment
treatments, there were no marked differences (P>0.05) in survival and
growth in 5--19 day old larvae at the end of rotifer feeding. However, the
larvae fed the AA enriched rotifers prior to the handling stress of transfer
to the aquaria demonstrated daily and significantly (P<0.05) lower
accumulated mortality after transfer and during Artemia feeding than larvae
fed the AA-deficient (DHA-PL) and ALGA-enriched rotifers. As larvae fed the
ALGA, rotifers partially retroconverted DPA to AA in their tissues, the
final survival (31.0%) in these larvae was markedly better (P<0.05) than
larvae fed the DHA rotifers (17.5%), but significantly (P<0.05) lower
than larvae ingesting AADHA rotifers (42.9%). Conversely, the
high-accumulated mortality in larvae fed the AA-deficient rotifers could not
be corrected during the post-handling phase by feeding AA supplemented
Artemia. The results suggest that dietary AA fed prior to handling stress
improved survival more effectively than when fed following handling stress.
These findings imply, as well, the importance of early larval nutrition on
later larval and juvenile survival during crowding, grading and other
handling stressors.
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