SELECTING EQUIPMENT FOR PRODUCING
FARM-MADE AQUAFEEDS
John Wood
Grain and Food Processing Section
Natural Resources Institute
Central Ave., Chatham Maritime, Kent ME4 4TB, U.K.
WOOD, J. 1993. Selecting equipment for producing farm-made aquafeeds, p. 135-147.In
M.B. New, A.G.J. Tacon and I. Csavas (eds.) Farm-made aquafeeds. Proceedings of
the FAO/AADCP Regional Expert Consultation on Farm-Made Aquafeeds, 14-18
December 1992, Bangkok, Thailand. FAO-RAPA/AADCP, Bangkok, Thailand, 434
p.
INTRODUCTION
When addressing the subject of preparing feeds for fish it is important to recognise that
we are in fact seeking to prepare a foodstuff with specific nutritional and physical
properties to meet the differing feeding habits of a range of aquatic consumers. The
purpose of the feed manufacturing process is therefore to prepare a food which, as far as
possible, meets the gastronomic habits of the target consumer. The need to prepare feeds
for slow and fast feeders, water surface, mid water or bottom feeding species has been
well recognised.
If a farmer is to be successful in feed preparation it is important that he examines the
options available to him. In practice, most farmers have come to believe that pelleted feed
is the most desirable since this is the feed form which has resulted in high yields on what
are perceived to be financially successful large commercial fish farms. This is an
understandable conclusion to make but its validity on a nutritional and practical basis still
requires solid confirmation for semi-intensive culture. Nevertheless, in this paper we will
consider the factors affecting the selection of equipment, principally for making feeds of
high water stability in pellet or noodle form, since these types of feed potentially enable
the maximum number of consumers to be fed at any one time. This paper will outline the
principles behind equipment selection, and in particular comment on the properties of
feed raw materials which will influence such decisions.
WHAT DO FARMERS WANT?
In seeking to meet the requirements of the fish we must also examine the requirements of
the farmer. What are his objectives and are they achievable? The two may not necessarily
be compatible in all cases. Annex 1 summarises the primary objectives of the farmer
concerning feed preparation, but the degree to which they are achievable will vary from
farm to farm, region to region and country to country. There is no single solution that will
be practical and cost effective for all farm-made aquafeeds. We are assuming that the
farmer already has a feeding strategy but wishes to improve upon it.
FACTORS INFLUENCING THE SELECTION
AND INSTALLATION OF FEED PROCESSING EQUIPMENT
The supplementary feeding of cultured fish has become an established practice in many
parts of the world and numerous designs and sizes of machines have been used for farm
and commercial feed manufacture. Some farmers have made wise choices while others
have regretted expenditure on equipment which has failed to perform adequately with the
raw materials available, or was of an inappropriate capacity.
If a farmer is starting a new venture there are important factors to be evaluated before any
selection of specific equipment should be considered. The response to their evaluation
will then form the framework for determining the machinery requirements to meet the
feed production objectives within the financial resources available (see Annex 2).
This evaluation of interacting factors must be conducted with an understanding of the
physical and functional properties of the raw materials available. These aspects will be
discussed in more detail later in this paper.
PROCESSING EQUIPMENT OPTIONS
There are many and various options for processing equipment for aquafeed processing, as
can be seen from the practices of aquaculturists in any locality. Processing equipment
options include electric or petrol/diesel engine driven machinery, and also the use of
hands and feet. The most common processing operations can be summarised as:
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raw material size reduction;
raw material blending;
feed forming;
feed drying.
The range of equipment options within each processing operation are summarised in
Table 1. It is not appropriate to describe these machinery options in detail since almost all
are well known and specific details can be obtained from manufacturers.
Table 1. Options for feed processing equipment
Process operation
Equipment
Raw material/product
Mortar and pestle
dry or moist grinding or blending
Size reduction
Mincer
wet materialse.g. trash fish/offals
Hammer mill
coarse-fine dry materials
Plate mill
coarse-fine dry materials
Physical
Hand
for small quantities variable efficiency
Blending
Feet
Mechanical mixers Bowl
moist doughs
Forming
Drying
Hand
Mincer
Pelleter
Cooker extruder
Solar
Mechanical
Horizontal dry powders or moist crumbs
Vertical dry powders
dough ball
moist noodles
dry pellets
semi-moist/dry pellets or noodles
variable efficiency
controlled drying
The choice of equipment will be limited firstly by financial resources, secondly by the
desired water stability of the feed (and thus raw materials availability), and thirdly by the
required scale of feed manufacture. However, on the assumption that finance is not
limiting and all forms of machinery are potentially available, then the factor which will
govern machinery choice is the spectrum of raw materials on offer for feed formulation
and manufacture.
FUNCTIONAL PROPERTIES OF FEED RAW MATERIALS
Commercial fish feed manufacture is predominantly associated with the processing of dry
ingredients and the manufacture of a dry product. This is not necessarily the case for farm
feed manufacture. Commercial processors require dry products for long term storage and
transport. Farm feeds can utilise local raw materials which may be:
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high in moisture and of short shelf life;
of insufficient quantity to become commercially viable;
grown on the farm or be a byproduct of local agriculture;
available during certain seasons only;
having functional properties which have not been damaged through industrial pretreatment.
The question which must then be asked is: “In what way can the nutritional and physical
characteristics of the raw materials available meet the desired nutritional requirements of
the fish to be farmed, and be in a form which will stimulate feed intake and be water
stable throughout the feeding period?”
To enable this question to be addressed we should consider the general functional
properties of feed nutrients and the effect which moist heat is likely to have on them. The
functional properties of raw materials, or more specifically of feed nutrients, are those
which affect the ability of feed materials to:
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cross bond with each other;
alter their viscosity characteristics;
change from granular to plastic consistency;
release bound moisture;
induce water stability.
The effect of moist heat on the functional properties of feed raw materials is important
since this is the kind of treatment which many are subjected to during processing before
they, or their byproducts, are actually considered as raw materials for fish feed (or other
animal feed).
The important functional properties of the major nutrients are summarised in Table 2.
These properties are, of necessity, expressed in general terms since there are differences
in specific properties depending upon the source of the nutrient. From Table 2 it is
evident that the nutrients with the most important functional properties are the proteins
and the starches. In most circumstances, both nutrients will also be present in high
proportion in the mixed diet and therefore have the potential to significantly alter its
properties. Let us examine the functional properties of these two nutrients in a little more
detail.
Table 2. Functional properties of feed nutrients
Change in functional
Nutrient
Normal state
Effect of moist heat
property
vapourization
energy transfer
Water liquid
colloidal fibrous
soluble/hydrable to
denaturing
Proteins
globular viscous
insoluble
insoluble granule to soluble
gelatinisation
Starches inert granules
gel
some cross bonding with difficult to extract with
liquid or solid
Fats
starch amylose
organic solvents
fibrous
minimal
minimal
Fibre
soluble solid or
reaction with lysine
minimal
Sugars
liquid
caramelization
soluble or insoluble
minimal
minimal
Minerals
solid
soluble or insoluble
some heat labile
minimal
Vitamins
solids
Starches
In their native state starches, whether from cereal or root crops are found in the form of
starch granules which are essentially inert when placed in cold water. They resist water
absorption, and there is minimal adhesion between granules. In this form starches are also
of low digestibility to aquaspecies, and have minimal properties for binding other feed
components. It is only when starches are heated in water, causing the granules to rupture
and gelatinise forming viscous pastes and gels, that starch has desirable properties for
binding feeds.
However, since the starch has also become more soluble during the gelatinisation process
(a property which is retained after rapid starch drying), feeds bound with gelatinised
starch alone will disintegrate as the feed hydrates and continues to absorb water, although
the degree of binding is considerably better than when feeds contain no gelatinised starch.
Proteins
In their native or natural form, proteins associated with plants tend to be “globular” in
shape whereas animal proteins are more characteristically “fibrous” in form. Apart from
those proteins which are totally insoluble, such as those comprising wool, silk and hair,
proteins are soluble in water, salt solutions or mild alkaline or acid solutions. When
subjected to heating, proteins tend to coagulate or denature. This is a process which is
well recognised during the cooking of egg albumin, when the raw soluble protein is
converted to an irreversibly insoluble protein gel.
PROCESSING OPTIONS
To illustrate the potential interactions of raw materials let us examine what processing
options could be available to a farmer for fish feed production. For example, let us
consider the use of three raw materials potentially available in many developing countries
i.e. trash fish, sun dried cassava and full fat soya beans. These raw materials may be
described in the following way:
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trash fish: hydrated, fibrous protein, with some fat associated, but no starch;
cassava: non-hydrated starch granules with little protein or fat;
full fat soya beans: non-hydrated globular protein with high association with fat
and low in starch.
We will assume that each raw material will be used at the same dry matter level in each
feed, and that the blend of raw materials will meet the desired nutritional requirements of
the culture system being operated. The oil present in the soya beans is a required nutrient
for the diet.
Option 1
Let us assume a process whereby all three raw materials are treated individually as
industrial agro-products for processing and storage. They will then be blended to form a
feed of the desired nutrient specification.
RAW MATERIAL
Trash fish (souble
protein)
Cassava (inert
granules)
Soya beans
PROCESS OPTION
Hot air dried to fish meal
(coagulated protein) (denatured
protein)
No further processing (inert
granules)
Oil expelling; toasting of soya meal
EFFECT OF PROCESS
ON FEED BINDING
Loss of ability to cross link
with other proteins
Inert granules with no gelling
chractersisitcs
Loss of ability to cross link
(hydratable protein)
(coagulated protein)
with other proteins
Result: Three separate raw materials with no inherent ability to bond with each other.
These materials will require a binder and careful steam conditioning to partially gelatinise
the cassava before any degree of binding between particles can be obtained.
Option 2
RAW MATERIAL
Trash fish (soluble
protein)
PROCESS OPTION
Sun dried to produce fishmeal
(coagulated protein) (partially
denatured)
Cassava (inert
Cook in water (gelatinised starch)
granules)
Soya beans
Oil expelling; toasting of soya meal
(hydratable protein) (coagulated orotein)
EFFECT OF PROCESS
ON FEED BINDING
Partial loss of ability to cross
link with other proteins
Viscous base for aiding feed
binding
Loss of ability to cross link
with other protines
Result: Improved stability of the feed due to partial hydration of some fish proteins and
viscosity of gelatinised starch. Heat denatured soya proteins are inert and add little to
feed stability.(Note: Even slow sun drying results inpartial denaturation of fish proteins
such that rehydration does not result in the reformation of colloidal protein material).
Option 3
RAW
EFFECT OF PROCESS ON FEED
PROCESS OPTION
MATERIAL
BINDING
Trash Fish
(soluble
protein)
Blend the materials
Formation of intermeshing matrix of proteins
Cassava
together and co-extrude and starch which are respectively denatured
(inert granules)
while heating
and gelatinished simultaneously
Soya beans
(hydralable
protein)
Result: This process will give the most effective bonding between the feed components,
and thus the maximum feed stability. The process is in effect that which occurs during the
process of cooker extrusion, and is the reason why this process has become so popular
amongst commercial fish feed manufacturers. Furthermore, when using full fat soya as a
raw material, the process enables the destruction of the trypsin inhibitors which would
otherwise significantly depress protein digestion and assimilation by the fish.
A further advantage of this form of processing is that it can incorporate wet fish as an
ingredient into the feed mixture without the need for pre-drying, or the need to extract the
oil from soya beans prior to their use.
ARE THESE METHODS APPROPRIATE FOR
FARM-SCALE AQUAFEED MANUFACTURE?
The foregoing options illustrate the desirability for the controlled processing of proteinand starch-containing raw materials by methods which will maximise the effects of their
functional properties. Feed materials must be examined in terms of their physical or
functional properties and not solely as sources of nutrients.
On many fish farms, feeds are being prepared which take into account the factors
discussed above. The benefits of cooking starchy bases such as cassava or rice have been
recognised, both for developing the viscous gelatinisation of starch and the resulting
improvement in digestibility.
However, the stability of formulated feeds which include cooked starches may also be
due to a degree of starch retrogradation during cooling and sun drying. During
retrogradation, starch gels tend to lose their consistency as starch molecules and form into
crystalline structures (for example, starch retrogradation is often associated with the
staling of bread). Once a starch has retrograded it is often more difficult to solubilise, and
is less readily hydrolysed by enzymes. From a fish feed perspective therefore, starch
retrogradation in association with a protein matrix may enhance feed resistance to
disintegration in water. The negative effect will be reduced starch digestibility.
Where farmers use trash fish as their base, they are introducing a valuable source of both
nutrients and functional characteristics to the feed. For example: a Thai farmer produced
his own feed for freshwater prawns from the following ingredients: wet trash fish
(44.4%), fish meal (13.3%), rice bran (6.8%), soya meal (8.9%), poultry feed (13.3%),
and broken rice (13.3%). The rice was cooked to a thick paste and then mixed with the
ground dry ingredients and the minced trash fish. The moist dough was then formed into
strands through a mincer die plate, and the product sun dried on a concrete pad. The dried
feed, which had a water stability of more than 24 hours in static water before
disintegration took place, was bound with gelatinised and partially retrograded starch and
by the matrix of partially denatured fish proteins produced during sun drying. Of
particular interest is the addition of poultry feed. The farmer commented that it had been
added to the feed mix to overcome the tendency of the fibrous rice bran to break the
structure of the pellet during drying. Practically and nutritionally, the farmer may have
had the same success by removing the rice bran and poultry feed from the diet and
replacing them by soya meal and broken rice.
The process used in the preparation of this feed was quite labour intensive but, since the
farmer was able to obtain most of his dry materials in a pre-ground form, his machinery
requirements were reduced to a mincer and a simple heated bowl for cooking the rice.
The mincer also served as the device for shaping the feed dough into long strands for sun
drying prior to crumbling to feeding size pellets, and for storage.
This situation is, however, not typical of fishfarms which are situated away from coastal
regions, where supplies of trash fish are non-existent. The only ingredients available may
be the byproducts of other agro-industries which have heat treated the materials and
denatured the proteins during processing, e.g. in oilseed cakes. Under these
circumstances farmers may be able to obtain sufficient raw materials to meet the nutrient
requirement of the culture system being operated, but have few materials which will help
in developing any degree of water stability. The most sophisticated machinery will be of
little use to the farmer unless he is able to obtain additional raw materials to induce
binding, while maintaining the nutritional integrity of the desired feed.
ENVIRONMENTAL ASPECTS
As aquaculture expands throughout the world there is a requirement that farmers use their
water resources wisely. This applies not only for the protection of their own stock, but for
the protection of those who will abstract pond discharge waters for other agricultural
uses, and also for the protection of the consumers of cultured species.
One of the first environmental requirements of an aquaculture farm is to maintain the
quality of the aquatic environment by attempting to ensure that feed added to the pond
reaches the target animal. This is the purpose of preparing water stable feeds.
A further requirement is to ensure the microbiological safety of aquatic feeding systems.
Since many animal proteins are associated with potential pathogens such as salmonella, it
is desirable that animal (including fish) proteins should be pasteurised before they are
ingested by cultured fish. This is particularly important should the trash fish have been
grown in septic ponds or other water courses potentially contaminated with faecal
material. Similarly animal viscera, such as poultry offal, should also be treated before it is
consumed by fish or other aquatic species. At the moment, few farm feed processors have
the facilities to pasteurise protein material of this kind while including it as valuable
nutrients and functional protein within feeds.
There is therefore a need to develop low cost farm scale feed processing equipment
which will enable raw materials to be processed to produce feeds with acceptable
microbiological and water stability characteristics. Of particular benefit would be a
heated die plate for attachment to a mincer or similar feed forming machine which would
act as a feed pasteurisation unit while also developing a degree of starch gelatinisation
and protein denaturation. However, such a device could not replace the functions of a
cooker extruder.
CONCLUSIONS
In presenting the above information an attempt has been made to demonstrate that the
selection of machinery for the manufacture of farm made aquafeeds is not a simple
exercise of selecting items from a catalogue in accordance with the quantity of feed
desired. It is important that machinery is selected in relation to the properties of the raw
materials available for formulating and processing. We are aware of what is desirable, but
the task is to select the most appropriate equipment for use with non-ideal raw materials.
This challenge will be much greater for some farmers than others.
Annex 1. Primary objectives of a farmer concerning feed preparation
Potential for
Objectives
achievement
Prepare feeds of ideal nutritional and physical quality which are
Maybe
cheaper than existing feeds
Use raw materials which are locally and constantly available,
Doubtful
Produce feeds that are attractive and non-polluting
Possibly
Utilize processing equipment which has low capital and running
Perhaps
costs and is available locally
Take minimal time and effort for processing
Uncertain
Have technology which is known only to him, is specific to his
unlikely
needs, and gives him an advantage over competitors
Have a technology which is operable by family members
Hopefully
Annex 2. Preliminary factors for quantifying desired aquafeed production
capability
Identify and evaluate the following:
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target animals and their feeding behaviour;
raw material availability and continuity of supply;
formulation options;
feasibility of obtaining the desired feed conversion and crop yield;
output of feed required in relation to fish growth phase;
desired frequency of manufacture in relation to fish growth phase;
characteristics of the proposed site: access, power supply and its reliability.
building design, storage facilities for raw materials and finished feeds, security:
desired lifespan of equipment;
possible future developments/expansion on site;
locally made or imported equipment;
process equipment options, flexibility, power requirements;
compatibility of options for formulations and equipment;
access to finance.