The effect of dietary
arachidonic acid on growth, survival, and cortisol levels in different-age
gilthead seabream larvae (Sparus auratus) exposed to handling or
daily salinity change
W.
Koven, R. van Anholt, S. Lutzky, I. Ben Atia, O. Nixon, B. Ron, A.
Tandler-2003
Aquaculture, 228(1-4): 307-320
Abstract:
The effect of dietary arachidonic acid (ArA) on
survival, growth, and cortisol level in different-age gilthead seabream
larvae exposed to handling or daily fluctuating salinity was tested.
Premetamorphosing (3–19 DPH) larvae were reared in 400-l V-tanks and fed
one of three rotifer treatments containing ArA levels of 1.14, 2.11, or 3.87
mg g-1. At 20 DPH, the larvae were divided into two groups where
each larval group was randomly divided over twelve 27-l aquaria (300 larvae
per aquarium) and the stress of transfer was defined as an acute stressor.
In each set of 12 aquaria, larvae were fed over 12 days three Artemia
metanauplii treatments, which were tested in four aquaria per treatment,
giving Artemia ArA levels of 0.59, 3.42, or 5.86 mg g-1
dry weight (DW). One set of 12 aquaria received seawater of constant
salinity (25ppt) and these larvae, exposed only to the stress of transfer,
were considered as controls. The other set of 12 aquaria was supplied with
seawater with a daily fluctuating salinity from 25ppt to 40ppt and back to
25ppt, exposing the larvae to 12 days of salinity change. Another trial was
carried out on 30 DPH metamorphosing larvae, which were similarly stocked in
the aquaria and tested with the identical Artemia treatments as the
premetamorphosing larvae study.
A positive correlation was found between increasing
dietary ArA level and survival at the end of the study in the control
premetamorphosing (20–32 DPH) and metamorphosing (30–42 DPH) larvae
(38%, 48.6%, and 77.2%, and 58%, 56.4%, and 90.4%, respectively). On the
other hand, premetamorphosing and metamorphosing larvae exposed to salinity
change, although exhibiting an increase in survival at the intermediate
level of ArA, demonstrated a decrease in survival (55.3%, 60.0%, and 25.8%,
and 70%, 83%, and 76%, respectively) when fed the highest ArA level. In the
control metamorphosing larvae, basal cortisol (6.0, 8.2, and 11.4 ng g-1
DW) was independent of dietary ArA while fish exposed to salinity change
demonstrated distinctly higher basal cortisol levels (7.5, 15.9, and 19.8 ng
g-1 DW) that markedly increased with rising dietary ArA levels at
42 DPH. Fish exposed to salinity change and fed Artemia containing
0.59, 3.42, and 5.86 mg g-1 ArA exhibited significantly (P<0.05)
decreasing SGR values (12.15, 10.68, and 9.69, respectively) while the SGR
values in the control larvae (10.23, 10.92, and 9.79, respectively) were
generally stable.
The results showed that dietary ArA promoted survival
in fish encountering only handling stress. In contrast, repetitive salinity
change altered the nature of the stress response where dietary ArA appeared
to upregulate cortisol synthesis coinciding with reduced growth and
increased mortality.
(Israel Oceanographic and Limnological Research, The
National Center for Mariculture, P.O. Box 1212, Eilat 88112, Israel, e-mail:
Koven@agri.huji.ac.il)