2. Table 1. Main lipid sources, inclusion levels and fatty acid composition
of diets containing fish, soybean and krill oil.
Results
Factorial analysis was used to deter-
Fish Oil Soy Oil Krill Oil mine the effects of salinity, dietary lipid
Chemical Composition Diet Diet Diet sources and their interaction. At harvest,
Inclusion of Lipid Sources no significant (P > 0.05) difference was
Fish oil (g/kg diet, wet basis) 26.7 0 0 observed in shrimp survival (93.1 ± 5.2%)
Krill oil (g/kg diet, wet basis) 0 0 48.3 among shrimp fed the three test diets,
Soybean oil (g/kg diet, wet basis) 10 34.5 4.5 regardless of salinity level. Feed intake
Cholesterol (g/kg diet, wet basis) 0 1.3 0 was significantly (P < 0.05) affected by
Soybean lecithin (g/kg diet, wet basis) 15 15 0 water salinity and diet type, although a
Marine:plant oil ratio 2.7 0 11 lack of interaction between these factors
Nutrient Levels remained until harvest. Shrimp mean
Total lipid content (g/kg diet, wet basis) 88.8 94 80.8 weekly growth was influenced only by
DHA (% total lipids) 2.54 0.3 1.6 diet type (P < 0.05).
EPA (% total lipids) 5.1 0.7 5.4 Shrimp grew less when fed diets with
HUFA (DHA + EPA) 7.6 0.9 6.9 fish oil or soybean oil – 0.91 ± 0.1 and 0.92
LOA (% total lipids) 28.3 44.7 16.2 ± 0.1 g/week, respectively – compared to
LNA (% total lipids) 3.4 4.9 1.5 those fed the krill oil diet (1.01 ± 0.1 g/
EFA (DHA + EPA + LOA + LNA) 39.4 50.5 24.7
week). Higher water salinity significantly
Peroxide Index (P < 0.05) depreciated shrimp final body
Total (meq/kg) 5.18 1.8 0 weight when compared to a lower salinity
for all diet types. Shrimp fed the krill oil-
enriched diet reached final body weights
was reduced to 70/m², and the 2.79 ± 0.6 First, shrimp of 1.71 ± 0.4 g were statistically higher than the weights of
g shrimp were fed the experimental diets stocked at a salinity of 29.73 ± 0.9 ppt for shrimp fed the fish oil and soybean oil diets
twice daily for nine weeks. a two-week acclimation period in 50 (Figure 1) at both salinity levels.
For the study on osmoregulatory tanks of 500 L. For eight days, shrimp Shrimp yields (553.1 ± 74.4 g/m²)
stress, a model was adopted using salinity were fed the diet with the lowest n-3 and biomass gains (315.2 ± 42.4 g/tank)
increases of 2, 3 and 4 ppt/day for five HUFA content. Five days prior to and were not statistically different among diet
days with four levels of n-3 HUFAs: 1.1, during salinity increase, shrimp were fed type or salinity level. A gas chromatogra-
2, 2.6 and 3.3% of total lipid content. the experimental diets. phy analysis revealed that the HUFA
global aquaculture advocate November/December 2009 59
3. Table 2. Fatty acid profiles (% of total lipid content) of tails after L. vannamei were fed
various dietary lipid sources under ideal and hypersalinity water conditions for nine weeks.
Fish Oil Diet Soybean Oil Diet Krill OIl Diet
Fatty Ideal High Ideal High Ideal High
Acid Salinity Salinity Deviation Salinity Salinity Deviation Salinity Salinity Deviation
DHA 7.13% 5.34% -25.08% 3.69% 3.53% -4.36% 6.55% 4.22% -35.59%
EPA 12.42% 10.09% -18.78% 6.61% 6.6% -0.08% 14.96% 11.5% -23.15%
LOA 14.64% 14.93% 1.99% 27.31% 26.94% -1.36% 11.63% 11.1% -4.58%
LNA 0.69% 0.63% -8.48% 1.21% 1.3% 7.01% 0.67% 0.54% -19.37%
12.5 content of shrimp tails for animals sub-
Ideal Salinity High Salinity jected to high-salinity rearing conditions
was reduced (Table 2).
12
Shrimp fed the fish oil and krill oil
Body Weight (g)
diets showed at least 40% higher HUFA
11.5 concentrations in their tails than shrimp
fed the soybean oil diet under ideal salin-
11 ity. Contents of linoleic acid (LOA) and
linolenic acid (LNA) in shrimp tails were
higher in animals fed the soy oil-enriched
10.5 feed at both salinity levels. In the osmo-
reglatory stress study, after a five-day
10 increment in water salinity, final shrimp
Fish Oil Soy Oil Krill Oil
Diet Diet Diet survival differed in accordance to salinity
Figure 1. Shrimp final weight after 64 days of rearing. concentration (P < 0.05).
Survival was lower in the treatments
subjected to lower increases in water
30-40 ppt 30-45 ppt 30-50 ppt
salinity (Figure 2). In the group exposed
120 to daily salinity increases of 4 ppt, 100%
shrimp mortality was observed. HUFA
100
supplementation levels provided no bene-
fit to shrimp survival. There was no sig-
Survival (%)
80
nificant interaction between water salinity
60 and HUFA levels for shrimp survival.
40 Perspectives
This study showed that lipid source and
20 docosahexaenoic acid (DHA) and eicosap-
entaenoic acid (EPA) levels in the diet can
0 influence the growth performance and tail
1 2 3 4 5 fatty acid profile of L. vannamei farmed
Day under hypersalinity conditions. The diet
Figure 2. Cumulative shrimp survival after abrupt increases in water salinity. Shrimp were with krill oil supplementation was found to
fed diets containing DHA at 1.1, 2, 2.6 and 3.3% of total lipid content. promote better shrimp growth under both
ideal and high salinities over diets contain-
ing fish and soybean oils.
It is noteworthy to point out that the
high quality standards (as indicated by
peroxide analysis) and the presence of
high amounts of astaxanthin in the krill
oil may have provided further advantages
over the other lipid sources. However,
n-3 HUFA supplementation did not
appear to counteract the effects of acute
osmoregulatory stress.
Results from the study suggested that
supplementation of krill oil can be effec-
tive against a persistent hypersalinity con-
dition if farmers adopt a precautionary
strategy rather than a reactive one. As
salinity generally changes in shrimp farms
Experimental shrimp at harvest. relative to seasons, hypersaline conditions
can be easily anticipated.
60 November/December 2009 global aquaculture advocate
