January | February 2012
Feature title: Redefining mineral requirements: Why it’s necessary?
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FEATURE FEATURE
for many higher organisms, but for fish only the The higher the bone content of the fishmeal complex is carried out for each species the effi-
commercially valuable species have received sig- the more zinc needs to be added, espe- ciency of mineral supplementation can be hugely
nificant attention. Numerous studies have been cially when using an inorganic zinc salt. The improved. It would also reduce the problems
carried out on rainbow trout, Atlantic salmon replacement of fishmeal with plant protein may (lower availability and excessive mineral excretion)
and Channel catfish; these species have well exacerbate this effect. Rainbow trout fed a associated with higher levels of mineral inclusion,
defined and frequently cited requirement levels. soyabean meal based diet required 150mg Zn/ which is required when using more sustainable
These requirement levels tend to be cal- kg to achieve optimal growth. The increased animal and plant based protein sources. ■
culated using purified (non-realistic) diets and use of sustainable fishmeals, often from trim-
inorganic forms of the minerals. In reality, aqua- mings high in bone content, and plant protein References:
necessary?
culture diets contain anti-nutritional factors sources high in phytate may mean that a set of
t
Why is i
Bury, NR, Walker, PA, Glover, CN, 2003. Nutritive
(ANFs); these are components of the feed that minimum requirement levels for fish fed more
Redefining mineral requirements: inhibit the uptake or utilization of another part of
the feed. When concerned with mineral digest-
realistic diets will be of more practical use to
the industry.
metal uptake in teleost fish. J Exp Biol. 206, 11-23.
Davies, SJ, Rider, S, Lundebye, A-K, 2010. Selenium
and zinc nutrition of farmed fish: new perspective
ibility and availability two of the main ANFs are The development of more advanced feed
in feed formulation to optimise health and
tricalcium phosphate and phytate (phytic acid). supplements such as proteinate sources of min-
production. In: Bury, NR, and Handy, RD (Eds)
Tricalcium phosphate is found in the bone tissue erals may reduce the effect of ANFs on mineral surface chemistry, bioavalability and metal
by Dan Leeming PhD Research Student, Aquaculture and Fish Nutrition Research Group, University of Plymouth, Uk of animals and phytate in many plant proteins. availability. Mineral proteinates bind the mineral homeostasis aquatic organisms: An integrated
These ANF’s bind to minerals such as zinc within their structure, ‘protecting’ the mineral approach. SEB, London, pp. 159-181.
and effectively render them unavailable to the from the ANFs.
Lorentzen, M, Maage, A, 1999. Trace element status
T
fish. An example of the effect of these ANFs can This relationship between the protein and
of juvenile Atlantic salmon Salmo salar L fed a fish-
he increasing development of How does the fish obtain zinc? How and where is zinc used? be seen in rainbow trout. Rainbow trout have a the mineral is complex. The mineral has to be
meal based diet with or without supplementation
aquafeed technologies embraces a Fish have two routes of zinc uptake, first from Zinc is very highly regulated in all aspects of requirement of 15-30mg Zn/kg diet (Ogino and bound tight enough not to be released in the gut of zinc, iron, manganese and copper from first
new generation of feed ingredients the diet and second from the surrounding water. the fish’s body: its uptake from the water or the Yang, 1987). This was calculated using a purified where it would be a free mineral ion, susceptible feeding. Aquac. Nutr. 5, 163-171.
and additives leading to changes in There is the potential for waterborne zinc to be diet; its excretion by the gills, the intestine, the egg albumin diet, with no ANFs, and using an to the ANFs, just like an inorganic salt, but the
Ogino, C, Yang, G.Y, 1978. Mineral requirements in
the specification of diet formulations. absorbed in both the gut, from the swallowed urine or the integument; and also by its distribu- inorganic zinc sulphate. When a practical diet mineral still needs to be available to the animal
fish.4. Requirement of rainbow-trout for dietary
external water, and also directly from the exter- tion within the body. containing fishmeal was used an additional 40mg once it has been taken into the cells.
zinc. Bulletin of the Japanese Society of Scientific
This necessitates a new understanding of nal aqueous environment via the gills. This regulation means that even a dietary Zn/kg diet (probably bringing the total dietary If the correct protein/mineral complex is
Fisheries. 44, 1015-1018.
mineral nutrition and the need to redefine trace Salmonids “drink” very little, especially when level of 1700mg/kg ZnSO4 is still non-toxic to zinc level closer to 80-100mg Zn/kg diet) was used the level of the mineral used in the diet
element requirements in keeping with intensive in freshwater; freshwater zinc levels are usu- the fish. The ability to regulate this appears to required to maintain normal growth. can be reduced by as much as 70 percent Paripatananont, T, Lovell, RT, 1995. Responses
production whilst promotion of fish health. ally less than 10µg/l and saltwater levels even come from the intestine, it is thought that excess Similarly, Atlantic salmon fed a fishmeal diet (Paripatananont and Lovell, 1995; channel catfish of Channel Catfish Fed Organic and Inorganic
Sources of Zinc to Edwardsiella ictaluri Challenge.
This short review gives a basic outline of lower. This is considered too low to make any zinc is simply not absorbed and passes through containing 65mg Zn/kg could not maintain their with zinc methionine).
Journal of Aquatic Animal Health. 7, 147-154.-
the biological mechanisms involved in one of significant contribution to the whole body zinc the fish in its faeces, however, it hasn’t been normal zinc status (Lorentzen and Maage, 1999). If research into the type of protein/mineral
these trace elements, zinc and describes why levels even though the gills affinity for zinc is proved that the high levels of zinc remaining in
it’s important to re-evaluate the mineral require- extremely high. the faeces hasn’t been processed by the liver
ments for salmonids. However, even with this high affinity the and excreted back into the faeces in the bile.
uptake rate of zinc from the gill is three to four Either way, excess zinc in the diet does not
Why is zinc important? times lower than from the gut (Bury et al, 2003). seem to present a problem. Low dietary zinc
‘Micro-nutrients’ is a generic term for die- The uptake mechanism in fish is described as levels are however more serious and the regula-
tary components required in small quantities. high affinity low capacity in the gills and low tory mechanism more complex.
Minerals such as copper, zinc, iron, manganese affinity but high capacity in the gut. Every tissue of the fish can be broadly
and selenium are all micronutrients although
they are usually categorised as trace minerals,
This supports the theory that despite the
high affinity for zinc in the gill, dietary uptake is
grouped into one of two categories; either
functional or exchangeable. A functional zinc RESOLVING THE BOTTLENECKS
and are essential for the health of all animals,
including fish.
the major contributor to the body zinc status.
Free zinc ions (i.e. not bound to other com-
pool, such as the liver, fins, eyes, gills and skin are
generally considered metabolically important.
IN AQUAFEED
In aquaculture these dietary essentials are pounds) are potentially very toxic to many bio- It is these tissues, which maintain their zinc through innovation and expertise
often supplemented as part of a vitamin/ logical processes, yet the incorporation of these concentration regardless of the dietary levels.
mineral premix due to the inadequate supply free zinc ions in numerous proteins is vital for Exchangeable pools seem to be less important
obtained from many commercially used feed these very same biological processes to function. metabolically but it is in these tissues (bone,
smart aqua additives
ingredients. Thankfully, from a toxicological stance, only muscle, intestine) we see fluctuations in zinc for sustainable and cost-efficient aquafeed
Zinc is the most abundant trace mineral a very small fraction of the total zinc in the levels corresponding to the dietary levels.
found in fish. It is essential for growth, the environment is in this “free” state. When the dietary supply exceeds require- AQUAGEST® AQUASTIM®
development and maintenance of healthy Unfortunately, from a nutritional stance, the ment these tissues increase in zinc concentration Digestibility enhancers Immune-modulators
bones, and over 300 proteins require zinc as majority of zinc in the environment is therefore and act as a storage facility and when the diet is
either a structural of functional co-factor. These unavailable. For the zinc to become available deficient it is these pools that decrease quickly AQUABITE® SANACORE®
include approximately 20 metalloenzymes such these compounds need processing in some way. and allow the metabolically important tissues to Attractants and palatability enhancers Natural growth promoters
as alkaline phosphatase (required for bone min- This processing occurs when the compound maintain their zinc levels. Regardless of the ability
APEX® AQUA NUTRI-BIND AQUA
eralisation/formation), alcohol dehydrogenase is digested, freeing the potentially toxic zinc of the fish to regulate zinc within its body the
Bio-active herbal extract Low inclusion binders
(required for fructose metabolism) and carbonic ion, which can now cross the intestinal barrier; turnover of zinc is relatively fast (~1% per day).
anhydrase (required to aid the removal of CO2 or breaking the large compounds down into This means that in order to avoid deficiency
from cell respiration). their smaller components, which can cross the a continual supply of dietary zinc is essential
Fish deficient of zinc shows growth intestine and take the zinc with it. Once inside (Davies et al., 2010)
retardation, cataracts, fin and skin erosion, the organism any free zinc is usually bound to
increased mortality rates and taste dysfunc- another compound generally termed a chap- Dietary zinc requirements www.nutriad.com
tion resulting in reduced appetite and feed erone, ready to be used or transferred around Research into mineral requirements, espe-
conversion. the body. cially trace minerals such as zinc is well defined
28 | InternatIonal AquAFeed | January-February 2012 January-February 2012 | InternatIonal AquAFeed | 29
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