The Cyprinids are the dominant species of culture fish worldwide accounting for over 20 million metric tons or 77 percent of the total aquaculture finfish production. The predominantly Asian consumption of this group of species makes them the most commonly eaten aquaculture species and importantly provides, as a food fish, a major source of basic protein to a large part of the world’s population.

1. November | December 2010
Feature title: Chromium
The International magazine for the aquaculture feed industry
International Aquafeed is published five 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 2009 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

2. T
he Cyprinids are the
dominant species of culture
fish worldwide accounting
for over 20 million metric
tonnes, or 77 percent of the total
aquaculture finfish production.
The predominantly Asian consumption
of this group of species makes them the
most commonly eaten aquaculture species
and importantly provides, as a food fish, a
major source of basic protein to a large
part of the world’s population.
The mirror carp (Cyprinus carpio) is one
of the most well-known members of the
carp family and is cultured widely in Asia, in
most parts of Europe including the former
USSR, in the Middle and Near East and in
some countries of Africa.
It is a hardy species that can tolerate
a wide range of conditions; however they
do best in large bodies of fresh water with
slow flowing or still water with soft muddy
sediments. Mirror carp are omnivorous in
that they feed on plants and animals such as
aquatic crustaceans including zooplankton,
insects, worms, aquatic plants, algae and
seeds.
The nutrient requirements for
many carp species have been well
documented and vary depending on the
particular species, farming method and
life history.
However, with the changing trends in
carp farming practise from extensive cul-
tivation to high input semi-intensive and
intensive culture systems the demand for
compound aquaculture feeds for this sector
is increasing. The average amount of fish
meal in carp diets is reported to be five
percent however diets intended for high
input systems can contain as much as 15-25
percent fishmeal.
These high levels of fish meal inclusion
are both expensive and considered unsus-
tainable in modern intensive aquaculture
practice.
Carbohydrates
In order to provide least cost compound
carp diets the trend is to use locally avail-
able vegetable protein sources and also
include non-protein sources to minimis-
ing nitrogenous wastes and environmental
impact. Carbohydrates, such as dextrin and
the starch binders, are important compo-
nents of these compound feeds, as they are
relatively inexpensive energy sources.
In general while fish have all the major
enzymes present for the digestion of carbo-
hydrates. The freshwater and warm water
fish digest carbohydrates more efficiently
than marine and coldwater fish.
Amylase is the main enzyme involved in
hydrolysing dietary starch into disaccharides
and trisaccharides which are converted by
other enzymes to glucose to supply the
body with energy.
However, amylase activity in the diges-
tive tract and the digestibility of starch in
fish is lower than that of terrestrial animals:
34 | InternatIonal AquAFeed | november-December 2010 november-December 2010 | InternatIonal AquAFeed | 35
Chromium:the forgotten mineral that plays an essential role in the utilization of
carbohydrates in mirror carp (Cyprinus carpio) diets
by Arafat R Ahmed and Simon J Davies, University of Plymouth, Plymouth, United Kingdom
Figure 1: Minerals in fish
nutrition
F: Chromium
r a i n b o w
trout have a
turnover of
glucose ten times slower than rats while
carp have a higher intestinal activity of
amylase than carnivorous fish.
This makes carp a suitable candidate for
the inclusion of higher dietary carbohydrate
levels than other carnivorous species.
The optimum range of dietary carbo-
hydrate for carp can be considered to be
30-40 percent, twice that of rainbow trout.
If carbohydrates are not provided as an
energy source then other nutrients in the
diet, such as protein and lipids, are diverted
and catabolised for energy production and
to provide metabolic intermediates for the
synthesis of other biological compounds.
Efficient compound diet
The importance of developing a better
understanding of carbohydrate utilisation
and its optimisation is therefore essential
in the development of efficient compound
diets for carp. Carbohydrate utilisation
appears to be related to the complexity of
the carbohydrate, for example, gelatinised
starch has been shown to produce higher
growth rates and feed efficiency in common
carp than dietary glucose or dextrin. This
indicates that complex carbohydrates are
digested and absorbed slowly while simple
sugars are absorbed rapidly and result in
high blood glucose levels.
Fish, in general, have been shown to have
poor control over glucose levels because
prolonged hyperglycemia is observed in fish
following glucose tolerance tests.This vari-
ation in carbohydrate digestion and absorp-
tion may be explained in several ways:
• The lack of inducible glucokinase and
low hexokinase activity, two blood
enzymes responsible for glucose
regulation.
• Glucose being
less potent than
certain amino
acids as a stimu-
lus for insulin
release.
• The possible
inhibition of
insulin release
by somatostat-
ins occurring
due to high
blood glucose
levels.
• The relatively
low number of
insulin recep-
tors in fish as
compared to
mammals.
In diet formula-
tions where plant
proteins are used
extensively, and
where they replace
fish meal in fish
diets, reduced
natural background
mineral levels occur.
Several areas of
concern arise due
to these diet for-
mulation changes:
balancing essential
amino acid content
of diets, diet palat-
ability and dietary
minerals, both in
terms of levels,form
and bioavailability.
In fish, trace
elements play an
important role in
cellular metabolism,
34 | InternatIonal AquAFeed | november-December 2010 november-December 2010 | InternatIonal AquAFeed | 35
F: Chromium
w w w. a a r s e n . c o m
High end
machinery
for top quality output
MICRO DOSING UNIT
• Wide dosing capacity range from
1 to 200 kg
• Durable construction and low
maintenance
• Special shaped dosing slides for fine and
coarse dosing
• Minimum contamination of product
• Wide dosing capacity range from

3. pancreatic beta cells and enhances the affinity
of insulin for its receptors.
Very few studies have been published on
chromium supplementation in fish.However
it has been shown that supplementation
with chromium chloride improved glucose
utilization in common carp while chromic
oxide improved utilization of glucose in
tilapia.
The chemical form of chromium has
been shown to affect the tissue concentra-
tions of chromium of rats and studies with
swine and poultry suggest that the inorganic
forms of chromium are poorly absorbed.
Further studies with the same species with
organic forms of chromium showed that a
chromium amino acid complex and yeast
incorporated chromium were more effec-
tive than the inorganic forms.
Research has been on-going at the
University of Plymouth to investigate the
effect of dietary chromium on the growth
and carbohydrate metabolism in mirror
and common carp. Preliminary results have
shown that an organic form of chromium
(chromium yeast, Biochrome®, Alltech
Inc) has shown improved growth results
and bioavailability than the inorganic form
(chromium chloride) when included in carp
diets’ at the same level.
Different parameters were measured
to evaluate the effect of various levels
and sources of chromium (organic and
inorganic) on fish health and this included
histological examination of the liver and gut,
comet assay for blood cells and the effect
of chromium on key liver enzymes, plasma
glucose concentration and gene expression.
Conclusion
This study will identify the true require-
ment of this essential trace element and
provide a better understanding of chromium
interactions in a number of physiological proc-
esses enabling more efficient diet formulation
for this important species to be developed.
eral metabolism and function but did not
explain why the responses change when
levels, sources and ratios of minerals varied.
When free ionic mineral forms are
used in fish diets, components of the diet,
such as phytate from plant proteins and
sulphur contained in many DDGS, may
form complexes with the trace elements
and interfere with their availability. Zinc and
copper are good examples of this.With the
presence of mineral antagonistic effects and
the resulting poorer bioavailability, the ten-
dency has been to compensate with higher
levels of traditional inorganic minerals.
Recent studies have shown that organic
mineral forms (metal amino acid com-
plex, metal polysaccharide complex, metal
proteinate and metal yeasts) are less sus-
ceptible to mineral antagonistic effects,
are better absorbed and therefore more
bioavailable. However the effectiveness of
these organic forms varies greatly depend-
ing on the production methodology and
the dietary components used for a particu-
lar target species.
Chromium
Due to the high levels of dietary car-
bohydrate in common carp diets, one
mineral of particular interest is chromium.
This trace element has been shown to be
essential and participates in carbohydrate
and lipid metabolism (see Figure 2).
Chromium supplementation improves
glucose utilization in diabetic humans and
its incorporation in animal feeds appears
to influence metabolic processes. This has
resulted in improved performance charac-
teristics (growth, reproductive efficiency
and carcass composition) in pigs, broilers
chicken and cattle.
The most important chromium oxida-
tion states are the trivalent and hexavalent
forms of chromium.The trivalent form being
the most stable and biologically important.
The acute and chronic toxic effects of chro-
mium are mainly caused
by the hexavalent form.
Trivalent chromium is
an active component of
the glucose tolerance fac-
tor (GTF) or chromium
di-nicotinic acid glutath-
ione complex (see Figure
3) which interacts with
insulin and facilitates the
uptake of glucose into cells.
Chromium is also consid-
ered to be a cofactor for
insulin,increases the size of
formation of skeletal structures, mainte-
nance of colloidal systems, regulation of
acid-base equilibrium and other physiologi-
cal functions. Many of the trace elements
are associated with specific proteins in
metallo-enzymes which have unique cata-
lytic functions and are involved in most
aspects of cell biochemistry and function
(see Figure 1).
Historically minerals and their inter-
actions in fish diets have been studied
individually (i.e. level of one mineral varied
while others are held constant) and only
the inorganic forms were investigated.
These studies explained much about min-
36 | InternatIonal AquAFeed | november-December 2010
About the author
ArafatAhmed is a PhD student at
the University of Plymouth with a
grant from the Ministry of Higher
Education in Bagdad,Iraq studying
the effect of dietary chromium
on the growth and carbohydrate
metabolism in mirror and com-
mon carp (Cyprinus carpio).
F: Chromium
Figure 2: The role of chromium
in glucose metabolism
Figure 3: The hypothetical
structure of GTF
Figure 4: Growth performance
of mirror carp fed respective
diets at weekly intervals for 8
weeks
36 | InternatIonal AquAFeed | november-December 2010
beautiful
GROWiNG iS
Our hydrolysates have a superior concentration of Natural Active NutrientsTM
Thanks to their biological action on fish and shrimp growth mechanisms,
they boost your feed performance and help you substituting fish meal.
contact@aquativ-diana.com - www.aquativ-diana.com
FRANCE/0033297404209

4. www.aquafeed.co.uk
LINKS
• See the full issue
• Visit the International Aquafeed website
• Contact the International Aquafeed Team
• Subscribe to International Aquafeed
Volume 13 Issue 6 2010
the international magazine for the aquaculture feed industry
Seaweeds as Ingredients
in Aquatic Feeds
A new and revolutionary type
of feather meal for fish feed
New dimension in the production
of hygienized feed meal
Chromium
- the forgotten mineral that plays an essential
role in the utilization
This digital re-print is part of the November | December 2010 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