Recent research by the authors evaluated strategies to reduce fishmeal and fish oil in diets for red drum by substituting terrestrial proteins and lipids while maintaining beneficial fatty acids with DHA supplements derived from marine algae. Results suggested fatty acid-enriched finishing diets can be used with growout diets containing little or no fishmeal and fish oil to achieve the desired DHA content in the final fish fillets

Arrington, Deliah

Browdy, Craig L.

Leffler, John W.

Seaborn, Gloria

Aquatic Commons

Marine fish are a nutritious component of the human diet,
providing important vitamins, proteins and essential long-chain
omega-3 fatty acids such as docosahexaenoic acid (DHA) that are
naturally abundant in marine food webs. Increasing consumer
demand for these species will likely be met through aquaculture.
Recent concerns related to the potential degradation of eco-
logical food chains, price instability and possible contaminants in
aquaculture feeds based on fishmeal and fish oil have generated
considerable interest in reducing or removing those fish products
from aquaculture diets. However, animals raised on no-fish diets
should still provide equivalent levels of the beneficial fatty acids
that make seafood especially healthy.
Recent research by the authors evaluated strategies to reduce
or eliminate fishmeal and fish oil in diets for red drum, Sciaenops
ocellatus, by substituting terrestrial proteins and lipids while main-
taining equivalent levels of beneficial fatty acids in the final prod-
uct by incorporating DHA supplements derived from marine algae.
Test Diets
Four growout and four finishing diets were tested (Table 1).
Each contained 44% protein, but lipid levels were 10% in the
growout diets and 15% in the finishing diets. Poultry meal
replaced fishmeal in diets 2, 2F, 3, 3F, 4 and 4F to maintain pro-
tein levels and palatability. Soy and flax oils replaced fish oil and
were balanced to maintain consistent n6:n3 ratios and lipid lev-
els in diets 3 and 4.
In order to produce a more healthful product for
humans, the finishing diets were developed with the goal of
increasing the concentration of DHA in fish during their
last four weeks before harvest. The lipid content of
growout diets 1, 2 and 4 was increased to 15% with the
addition of a commercial oil containing 40% DHA derived
from marine algae. Menhaden fish oil and flax seed oil were
added to diet 3 to increase its lipid content to 15%, as well.
Experimental Design
Juvenile red drum with a starting mean weight of
252.00 ± 2.78 g, bred and raised by the South Carolina
Department of Natural Resources, were fed commercial
fishmeal/fish oil diets prior to the experiment. Twelve
fish were stocked in each of 24, 1.4-m3 indoor tanks.
After two weeks of acclimation, three fish from each tank
Summary:
Recent research by the authors evaluated strategies to reduce fishmeal and fish oil in diets for red drum by substi-
tuting terrestrial proteins and lipids while maintaining beneficial fatty acids with DHA supplements derived from
marine algae. Results suggested fatty acid-enriched finishing diets can be used with growout diets containing little
or no fishmeal and fish oil to achieve the desired DHA content in the final fish fillets.
John W. Leffler, Ph.D.
lefflerj@dnr.sc.gov
Deliah Arrington
Marine Resources Research Institute
South Carolina Department of Natural Resources
217 Fort Johnson Road
Charleston, South Carolina 29412 USA
Gloria Seaborn
Center for Coastal Environmental Health and Biomolecular Research
Charleston, South Carolina, USA
Craig L. Browdy, Ph.D.
Novus International Corp.
Charleston, South Carolina, USA
feed and nutrition
Weight and length measurements of individual fish were collected
at the start of the experiment.
Fatty Acid
Composition of
Red Drum Maintained
By Fishmeal, Fish Oil
Substitutes in Diets
Table 1. Growout and finishing diets formulated and tested
in study with red drum.
Treatment Diet Type Description
1 Growout Control – 28% fishmeal, 6% fish oil
1F Finishing 28% fishmeal, 6% fish oil, 5% commercial oil
2 Growout 5% fishmeal, 6% fish oil
2F Finishing 5% fishmeal, 6% fish oil, 5% commercial oil
3 Growout 0% fishmeal, 0% fish oil
3F Finishing 0% fishmeal, 5% fish oil
4 Growout 0% fishmeal, 0% fish oil, 3.4% algal extract,
0.9% microbial product
4F Finishing 0% fish meal, 0% fish oil, 5% commercial oil
Commercial oil contained 40% DHA derived from marine algae.
Algal extract contained 15% DHA derived from microalgae.
Microbial product contained 12% arachidonic acid.
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were sacrificed, filleted and analyzed to provide baseline lipid
profiles of the edible flesh.
Diet treatments with six replicate tanks per treatment were
assigned in a randomized block design across three closed recir-
culating systems. Diets prepared in the lab were fed at 3% body
weight/day using automated belt feeders over a 20-week grow-
out period. Fish were batch weighed monthly, and feed rates
were adjusted accordingly. After 20 weeks, fish on the control
diet were approaching harvestable size at a mean weight of 719 g.
At that time half of the tanks in each treatment were switched
to finishing diets to enhance levels of DHA in the final product or
at least restore lipid profiles similar to those of the control fish.
Both the original diets and corresponding finishing diets were fed
for an additional four weeks. Three fish from each tank were har-
vested with individual weights and lengths measured and fatty
acid profiles determined for individual skinless fillets.
Production Results
The final weights of fish switched to the plant oil, DHA-
enriched finishing diets 1F, 2F and 4F for the final month of the
study were not significantly different from those for fish that
remained on the original diets during the finishing phase (Figure
1). When fish on diet 3 without fishmeal, fish oil or fatty acid
supplementation were supplied with fish oil as 5% of the finish-
ing diet 3F, their growth rate increased rapidly over those that
remained on the original diet.
By the end of the 24-week study, mean weights of the fish
fed the conventional fishmeal, fish oil diet 1 were not signifi-
cantly (P > 0.05) different from those for fish fed diet 4 with
fatty acid supplementation but no fishmeal or fish oil. Fish fed
both the low-fishmeal diet 2 and diet 3 without fishmeal, fish oil
or fatty acid supplementation lagged significantly in growth.
It is essential that red drum on no-fish diets receive fatty acid
supplementation, specifically docosahexaenoic and arachidonic
acids (DHA, ARA).
Fatty Acid Results
A goal of this study was not only to explore the production
potential of diets with no fishmeal or fish oil, but also to consider
the healthfulness of the product for human consumption in terms
of the beneficial fatty acid DHA. In all cases, fish switched to fin-
ishing diets high in DHA responded with increased accumulation
of this fatty acid in their tissues, independent of whether it influ-
enced growth rate (Figure 2).
Fish raised on diet 4 responded to the finishing diet 4F and
achieved tissue concentrations of DHA statistically indistinguish-
able from fish raised solely on the conventional fishmeal, fish oil
diet. The highest DHA levels were found in diets 1F, 2F – treat-
ments where a DHA-enriched finishing diet was used in conjunc-
tion with a fishmeal-based growout diet.
Fish fed diet 3 were significantly lower in DHA than those on
the other diets. With no DHA in their diets, these fish probably
survived only on stored reserves developed prior to this study.
1,400
1,200
1,000
800
600
400
200
0
Me
an
We
igh
t(g
)
Diet 1 Diet 1F Diet 2 Diet 2F Diet 3 Diet 3F Diet 4 Diet 4F
Growout Diet Finishing Diet
Figure 1. Mean weights of red drum after 24 weeks
of growout/finishing.
250
200
150
100
50
0DH
AC
on
ten
t(m
g/
1
g
)
Diet 1 Diet 1F Diet 2 Diet 2F Diet 3 Diet 3F Diet 4 Diet 4F
Growout Diet
Finishing Diet
Figure 2. DHA content of red drum fillets after 24 weeks
of growout/finishing.


Fatty acid composition of red drum maintained by fishmeal, fish oil substitutes in diets

http://aquaticcommons.org/14851/1/GAA-Leffler-Jan09.pdf

Fatty acid composition of red drum maintained by fishmeal, fish oil substitutes in diets

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