The turbot Psetta maxima is an important cultured flatfish species in Europe and now increasingly in China. Dietary formulations for this species typically have been dependent on high levels of fishmeal inclusion. Increasing costs and the decreasing availability of fishmeal have necessitated lowering fishmeal levels and increasing plant proteins in feed formulations.

1. May | June 2013
An effective source of dietary methionine
for the turbot Psetta maxima
The International magazine for the aquaculture feed industry
International Aquafeed is published six times a year by Perendale Publishers Ltd of the United Kingdom.
All data is published in good faith, based on information received, and while every care is taken to prevent inaccuracies,
the publishers accept no liability for any errors or omissions or for the consequences of action taken on the basis of
information published.
©Copyright 2013 Perendale Publishers Ltd.All rights reserved.No part of this publication may be reproduced in any form
or by any means without prior permission of the copyright owner. Printed by Perendale Publishers Ltd. ISSN: 1464-0058
INCORPORATING
f ish farming technolog y

3. T
he turbot Psetta maxima is an
important cultured flatfish species
in Europe and now increasingly in
China. Dietary formulations for this
species typically have been dependent on
high levels of fishmeal inclusion. Increasing
costs and the decreasing availability of
fishmeal have necessitated lowering fishmeal
levels and increasing plant proteins in feed
formulations.
In such diets methionine can become one
of the first limiting amino acids and supple-
mentation is frequently necessary to balance
diets and achieve optimum performance. The
hydroxy analog of methionine, 2-hydroxy-
4-methylthio butanoic acid (HMTBa) is a
safe and effective source of methionine that
has been used to supplement methionine
deficient diets for livestock and aquaculture
species.
HMTBa is structurally different from
L-methionine in that it has a hydroxyl group
instead of an amino group at the α-carbon
position, potentially reducing feed nitrogen
inputs into grow out systems. It is passively
absorbed and is converted to L-methionine
by D-hydroxy acid dehydrogenase and
L-hydroxy acid oxidase enzymes which have
been confirmed in tissues of shrimp and
fish. A two-part study was carried out at the
Ocean University of China, China to evaluate
1. The response of turbot fed diets sup-
plemented with either HMTBa (2-hydroxy-
4-methylthio-butanoic acid) or L-methionine,
and 2. The dynamics of absorption of HMTBa
and L-methionine.
Materials and methods
A 75-day growth trial was carried out
to evaluate the effects of HMTBa and
L-methionine as dietary methionine sources
on the growth of juvenile turbot (initial
weight 5.6 g. N=5 tanks per treatment).
Five levels (0.3, 0.6, 0.9, 1.2 and 1.5% dry
matter) of HMTBa (added as Mera™Met
– 84 percent HMTBa; Novus International
Inc., USA) and L-methionine were added
respectively to a practical basal diet, that was
limiting in methionine (0.59% methionine;
0.42% cystine; 1.01% total sulfur amino acids).
This basal diet served as the control diet
and contained 48 percent crude protein and
approximately 12.5% crude lipid.
A crystalline
L-amino acid
premix, which
was devoid of
sulfur amino
acids was added
to the basal diet
to approximate
the whole body
composition
of the turbot.
Different levels
of either HMTBa
or L-methionine
were added to
the basal diet
at the expense
of glutamic acid
to give total
methionine con-
centrations rang-
ing from 0.59
- 2.09 and total
sulfur amino acid
concentrations
ranging from
1.01 to 2.51%.
A second
study was
conducted to
evaluate the absorption of HMTBa and
L-methionine from diets containing these
methionine sources. The basal diet used in
the second trial was generally similar to that
used in the growth trial (0.75% methionine
and 0.45% cystine; total sulfur amino acid
concentration of 1.20%). The basal diet was
Figure 1: Weight gain and specific growth rate in juvenile
turbot fed either HMTBa or L-methionine
An effective source of
dietary methionine for the
turbot Psetta maxima
by Rui Ma1, Huapeng Hou1, Wenbing Zhang1, Anant Bharadwaj2, Craig Browdy2
and Kangsen Mai1
38 | InternatIonal AquAFeed | May-June 2013
FEATURE

4. supplemented with either 0.75% HMTBa or
L-methionine. In this trial larger fish (65 g; 45
fish/tank; N=3) were used to facilitate blood
sampling at the end of the trial.
The basal control diet and the two experi-
mental diets were fed to the turbot for a
period of 14 days twice daily to apparent
satiation. Fish were fasted 12 h prior to final
feeding. Following feeding, fish were sampled
at 0, 0.25, 0.5, 1, 2, 3, 4, 6, 9, 12, 18 and 24 h
respectively and their blood collected. Blood
was centrifuged and serum collected and
stored prior to analysis. Serum was analyzed
using HPLC for HMTBa and free methionine.
Results
There were no significant differences in
survival between treatments. Fish fed the
basal diet (red bar)
showed significantly
lower weight gain
than all the other
treatments (Figure
1). Weight gain
in fish fed both
methionine sources
increased in a quad-
ratic fashion with
increasing dietary
concentration. In
fish fed HMTBa
(blue bars) maxi-
mum response was
observed at 0.9%
supplementation
and was significantly
NUTRACEUTICALS AND PHYTOBIOTICS
FOR AQUACULTURE
Growth promoters
Anti-parasites
Attractants
Hepatoprotectors
Antioxidants
Detoxifiers
Chelated minerals
ADDITIVES FOR AQUACULTURE SOLUTIONS
C/ San Romualdo 12-14 • 28037 Madrid (Spain)
+34 902 15 77 11 • +34 91 725 08 00
liptosa@liptosa.com • www.liptosa.com
Figure 2a: Serum free-methionine concentrations in post-
fed turbot fed the control, L-methionine and HMTBa diets
Figure 2b: Serum HMTBa concentrations in fish fed diets
containing HMTBa
May-June 2013 | InternatIonal AquAFeed | 39
FEATURE

5. higher than the response seen in fish sup-
plemented 0.9% L-methionine. Generally, at
doses ranging from 0.6 to 1.5%, fish fed
HMTBa showed equal or higher weight gain
compared to fish fed L-methionine (green
bars). Similar responses were observed for
other performance parameters such as final
weight, specific growth rate, feed efficiency,
protein efficiency ratio and protein retention.
Results from the analysis of serum
show that the maximum serum concentra-
tion of free-methionine (435.13µmol/L) in
L-methionine-fed fish was observed at 9 h
after feeding (Figure 2a) whereas the maxi-
mum serum HMTBa level (426.17µmol/L) in
HMTBa-fed fish occurred 6 h after feeding
(Figure 2b). Appreciable quantities of HMTBa
were observed in the serum of HMTBa-fed
fish shortly after feeding as expected based
on passive diffusion of HMTBa across the gut
wall in fish. Two free methionine peaks were
measured in the serum of HMTBa-fed fish at
3-4 h and 12 h post-feeding. This suggests
contributions from either HMTBa metabolism
to L-methionine, tissue protein turnover or
digestion of intact dietary proteins. These
data suggest that HMTBa is absorbed into
circulation in fish shortly after feeding and also
show that the maximum serum concentra-
tions of HMTBa in HMTBa-fed fish are similar
to serum free-methionine concentrations in
L-methionine fed fish.
Conclusions
The results of these trials confirm that
HMTBa is a safe and available source of
methionine in practical diets for the turbot
Psetta maxima. The HMTBa was absorbed
efficiently into circulation at rates that are
similar or better than L-methionine. Dynamics
confirmed direct absorption demonstrated in
previous livestock studies. Mera™Met can
provide a cost effective methionine source
in reduced fishmeal formulations with 100
percent bioavailability. HMTBa has been
shown in previous studies to improve feed
attractability, providing an effective alterna-
tive for optimizing performance and allow-
ing for higher cost efficiencies through the
replacement of fishmeal by plant meals in
aquatic feeds.
More InforMatIon:
1The Key Laboratory of Mariculture, Ocean
University of China, China
Email: wzhang@ouc.edu.cn
2Novus International Inc., USA
Email: craig.browdy@novusint.com
Website: www.novusint.com
40 | InternatIonal AquAFeed | May-June 2013
FEATURE

6. May-June 2013 | InternatIonal AquAFeed | 41
FEATURE
CLOSER LOOK
take a
at Novus Aquaculture
® is a trademark of Novus International, Inc., and is registered in the United States and other countries. TM SOLUTIONS SERVICE SUSTAINABILITY
is a trademark of Novus International, Inc. ©2012 Novus International, Inc. All rights reserved. 2978
www.novusint.com/aqua
FEED COST REDUCTION | HEALTH THROUGH NUTRITION | OPTIMIZED RAW MATERIALS | FUNCTIONAL FEEDS | SUSTAINABLE PRACTICES
Our success in developing sustainable
solutions evolves from a hands-on knowledge
and understanding of the global aqua
industry. By focusing on the needs of the
animals, our team of experts will design a
solution for your operation.
International Aquafeed has teamed up with
www.lurestore.com to offer our readers a 15% discount
The world’s finest brass-based fishing lures
manufactured by hand in New Zealand
Your order will be processed and dispatched from our
production unit within 24 hours
Even fi sh farmers like fi shing!
www.lurestore.com
A & AJ Gilbert Fishing Tackle, New Zealand
REF: IAF303-PPL
Place your order today at
SPANISH
LANGUAGE
EDITION
www.aquafeed.co
EDICION
ESPANOLA

7. www.aquafeed.co.uk
LINKS
• See the full issue
• Visit the International Aquafeed website
• Contact the International Aquafeed Team
• Subscribe to International Aquafeed
They are what they eat
Enhancing the nutritional value of live feeds
with microalgae
Controlling mycotoxins with
binders
Ultraviolet
water disinfection for fish
farms and hatcheries
Niacin
– one of the key B vitamins for sustaining
healthy fish growth and production
Volume 16 Issue 3 2013 - mAY | Ju Ne
INCORPORATING
fIsh fARmING TeChNOlOGy
This digital re-print is part of the May | June 2013 edition of International
Aquafeed magazine.
Content from the magazine is available to view free-of-charge, both as a full
online magazine on our website, and as an archive of individual features on
the docstoc website.
Please click here to view our other publications on www.docstoc.com.
To purchase a paper copy of the magazine, or to subscribe to the paper
edition please contact our Circulation and Subscriptions Manager on the link
above.
INFORMATION FOR ADVERTISERS - CLICK HERE