As the name suggests, supplementary feeds do not have to provide a complete, balanced diet alone. Instead they merely add some extra nutrients to those already available to fish from the natural food production in the pond or waterway. Normally, a supplementary feed contributes mostly cheaper carbohydrate rich components. The fish can use these as an energy source, thus freeing more of the protein available from natural food sources to be used for growth. Poorer quality supplementary feeds, which are high in fibre and other components poorly digestible by fish, act more as fertilizers which stimulate production of natural foods in the pond. Thus the distinction between fertilization and supplementary feeding is not always clear.
Sources of supplementary feeds
An extensive range of agricultural and food industry products and by-products are suitable for use as supplementary feeds for farmed fish. The main factors determining which sources of supplementary feeds are best to use in a particular country or location include the fish species to be farmed, the geographic availability of potential feed components, quantities available (including seasonal fluctuations), competition for materials for use in human or domestic animal foods, price, transport and storage.
Sources of supplementary feeds can be grouped as follows:
(a) Plants and animals of aquatic origin
Many of the aquatic plants and animals are valuable foods for either human beings or for livestock. Of these, chestnut (Trapa natans) and lotus (Ipomea aquatica) are good for human consumption; water hyacinth (Eichornia crassipes), hornwort (Ceratophyllum demersum), and nariad (Najas guadalupensis) are good for cattle, sheep, goats, pigs and poultry; duck weeds (Potamogeton spp.) and reed leaves (Phragmites spp.) are good, both for farmed animals and for fish.
Of the aquatic animals, the group of wild trash fish is the largest one. Depending on the country, these are utilized either as food for human consumption or feed for farmed animals, including fish. In developing countries, they are seldom utilized as ingredients for fish diets, unless the production manager forbids the fishermen to take home these fish when they are gathered from the harvested ponds.
(b) Plant and vegetable production
Cereals. The main products of cereal production are grain and seed, while the by-products are straw or stems and/or cobs. With proper handling, there is practically no waste during harvest and/or storage.
The cereal grains or seeds are not used or feed for animals in developing countries, except on farms where intensive pig, poultry or egg production takes place.
In freshwater fish culture in developing countries their use can be envisaged only in the case of intensive or superintensive fish seed production (for breeders, fry and fingerlings); if economically justified, they can sometimes be used for intensive and semi-intensive culture of food fish in ponds, pens, cages or tanks.
By-products of cereals are used as feedstuffs for ruminants or as litter. In fish culture, cereal by-products are used as fertilizers before or after being used as litter.
The utilization of wastes derived from improper harvest and/or storage must be done carefully, because many kinds of dirty, mouldy or rotten seeds are not good for fish. They may cause enteritis or intoxication and therefore their suitability must always be checked locally, by trials.
Root crops. The surplus and uneaten parts of root crops, and the by-products such as leaves and stems, etc., are mainly utilized as feedstuffs for domestic animals. The tubers can be used after processing (by chopping, soaking, cooking, etc.) in intensive and semi-intensive fish production. The waste from tubers is also good for use in animal husbandry as well as in fish culture, provided it is not rotten or mouldy.
Legumes. There is a wide variety of leguminous plants, the main products of which are utilized for human consumption and feed for all kinds of livestock.
The seeds of the green forage plants (alfalfa, clover, etc.), and the pods and leaves of other species, are the by-products.
With proper handling there is little waste. Fresh alfalfa and clovers are good for ruminants, pigs and poultry as well as for herbivorous fish species.
Surplus quantities of beans, peas and soy are excellent feedstuffs for pigs, poultry and fish. The pods and leaves of these plants are good for ruminants and pigs.
Grasses. Fresh or as hay, these are used mainly as forage for ruminants. Pigs and ducks utilize most of them also. Fresh grasses are good for herbivorous fish especially grass carp.
Oil seeds. Fresh oil seeds are rarely used as feeding material, and when used they can be given only in small quantities due to toxicity. By-products (leaves, hay, stem) are utilized mostly in ruminant farming.
Vegetables. The surplus and the damaged parts of vegetables are good for most farmed animals. By-products (leaves, stems, pods) are utilized as well. In production, harvest and storage there is normally no considerable quantity of waste.
Fruits. The surplus and the cull of fresh fruits are frequently given to pigs and poultry and also to those fish which will consume them. By-products (leaves, wet-pulp, seeds, trunks) can be utilized mostly by ruminants. Waste resulting from improper handling and storage is often dangerous to feed fish, but can be used to raise the fertility of land or fish ponds.
(c) Products of animal husbandry
In animal husbandry the animal itself is the main product, and there are practically no by-products. The waste of animal husbandry, i.e., the manure, is one of the most important traditional materials to raise the productivity of the land, and fish ponds.
The quantity and quality of manure from various animals differ; the ruminants have the poorest and chickens/ducks have the richer manure.
(d) Products of the food industry
The milling industry. The main products are rarely used as feedstuffs, but all of the by-products are excellent. They are frequently used as energy-rich feeds for pigs, poultry and also for intensive and semi-intensive fish-culture. The wastes (mill sweepings) are good for fish.
Sugar production. The by-products of sugar production are utilized in cattle husbandry and in pig fattening. The wastes from it (lime-mud and sewage) can be utilized on land and in ponds as fertilizer.
Distilleries. The by-products of the different distilleries such as pomace, fresh or dry spent grain, malt germ and yeast, are good feeds for cattle, pigs, poultry and fish.
Oil production. Edible oil production is one of the most important and common food industrial branches. Depending on the oil production technology, oilseed meal (oil by extraction) and oilseed cake (oil by pressing) are very valuable by-products, due to their high protein content (30–70%).
Because of their attractive characteristics (the toxic or digestion-inhibiting effects of some of the oil seeds are eliminated during the production process), they are used as ingredients of balanced diets for all kinds of animals, including fish.
Vegetable/fruit processing and cold-storage plants. The by-products of vegetable and fruit processing are the various kinds of pomaces, mollasses, seeds, and skins, which either fresh or dry can be used as feedstuffs for ruminants, pigs, poultry and fish.
The quantity and quality of these by-products depend on the processing technology and handling. The wastes of vegetable and fruit processing and of cold-storage plants are the culled portion and parts of the raw material, and the sewage. These wastes can be utilized in fish culture directly as feed and indirectly as material to raise the natural productivity of fish ponds.
Slaughtering and meat processing. In slaughter-houses, blood, soft and hard wastes, hooves, horns and feathers can be considered as by-products which are utilized as feedstuffs with or without processing. If the quantity available is sufficient for economical processing, blood meal and bone meal are produced which are valuable ingredients for use in balanced diets, while in case of smaller quantities they can be fed freshly. The sewage of the slaughter-houses can be utilized as material to raise the natural productivity of fish ponds.
Pelleted feeds can be used either as supplementary diets in fish ponds or as complete diets in intensive culture systems such as raceways and floating cages. Formulations therefore vary greatly according to the technological characteristics of the culture system being used, as well as fish species (see Chapters 10 and 11). Formulations for various types of fishes are well described in various publications (e.g., New, 1987) and are therefore not considered here. Instead, only aspects of storage of feeds and ingredients, and the machinery necessary for dry pellet manufacture, are discussed below.
Storage of cereals
Cereal grain is a living material, and the life processes continue even after harvest. Cereal grains take moisture up from the environment, and release it under warmer conditions.
Like any living organisms, cereal grains respire. In the absence of oxygen, a so-called anaerobic respiration occurs. In principle, this is identical with alcoholic fermentation. This degradation process can be observed in wet grain stored in thick layers.
The wetter the grain, the more intensive the respiration. Respiration of air-dried grain (with 12–13% moisture content) is practically nil. It becomes marked if moisture content exceeds 15%; the loss in dry matter content is also significant.
Respiration is also influenced by the temperature of the grain and its environment (Table 3.1).
Table 3.1
RESPIRATION OF CEREAL GRAINS DURING STORAGE
| Moisture (%) | Temperature (°C) | CO2 produced during 24 hours (mg) |
| 14–15 | 18 | 1.4 |
| 14–15 | 30 | 7.5 |
| 14–15 | 40 | 20.0 |
| 14–15 | 52 | 248.0 |
Degradation of grain of high moisture content is caused mostly by intensive respiration. Respiration is the consequence of an enzyme activity which depends on the free moisture content of the grain. If air humidity reaches or exceeds 74%, propagation of moulds starts. Mouldy grain is not only unusable, but can even be toxic. Therefore, during storage the moisture content of grain should not exceed 14%, and air humidity should remain below 70%.
To ensure safe, degradation-free storage conditions, the following measures can be applied:
Only air-dry cereals should be harvested; if this is not possible....
Cereals should be dried.
if drying is done with warm air, the upper limit of temperature is 82°C with wheat for forage, 65°C with wheat for bread, and 43–48°C with barley and seed barley;
Cereals can be dried with cool air.
Chemical preservation is also possible.
Methods of storage
During hermetic storage, microbiological processes are inhibited. At a moisture content of 17–22%, few anaerobic bacteria or yeast fungi can propagate. Such storage is generally in silos.
Storage with ventilation. Cool air is blown through pipelines into the stored grain, which causes moisture and temperature to decrease.
Cold storage can substitute for drying, allowing the storage time to be prolonged.
Chemical treatment
Freshly harvested grain is treated with propionic or formic acid, then hermetically covered. At pH 2–3, microbiological processes are inhibited.
Cereals can be preserved after pre-drying. The specific energy consumption of this process is economic up to a dry matter content of 80%, it is then dramatically reduced. If cereal grain of 20% moisture content is treated with organic acids, energy can be saved and relatively dry grain is obtained.
Storage of feedstuffs
Bulk feedstuffs, such as cereals, leguminous seed, extracted bran and meals of forage plants, can be stored on the floor - indoors in barns, or outdoors covered with canvas or plastic. Feedstuffs can be picked up manually, or with various shovel or conveyor systems. The latter are of high capacity (40– 60 t/h).
Bulk feedstuffs or pelleted feeds can be stored in silos made of prefabricated concrete sections or metal sheets. Plastic foam is sandwiched between the two sheets for insulation. Air-blowing ventilators are mounted in modern silos. These not only cool the feedstuffs, but also decrease their moisture content.
Cereals of 19% moisture content can be stored without any degradation for 2–3 weeks at 20°C, for 4–5 weeks at 15°C or for 10 weeks at 10°C.
The bottoms of silos can be flat or conical. Small silos with conical bottoms can be unloaded by gravity, while big silos should have an unloading conveyor system.
Auxiliary facilities for storage and transportation are receiving hoppers, conveyor belts, trucks and trailers.
Storage in sacks, on loading pellets, is also a possibility.
Machinery for dry pellet manufacture
Complete diets for fish consist of various ingredients of plant and animal origin, minerals and synthetic premixes.
1. Production of pelleted feeds starts with the treatment of raw materials:
Grain cleaners: screens are used to remove extraneous matter.
Extracted brans, i.e., cakes or pellets left after the oil has been extracted (e.g., soy bean). These are crushed between steel rollers or tapers. From here the material is conveyed to grading screens.
There are several possible ways of preparing mealy substances:
ingredients can be conveyed to silos pneumatically
premix can be prepared from mealy substances (e.g., bran and meat meal are mixed in a 1:1 proportion so as to get a less fatty, easy-to-grind material)
meals applied for producing premixes, concentrates and supplementary substances can be directly poured into mixers.
Important aspects to be considered when preparing mealy substances are:
A 20 × 20 mm mesh screen should be placed in the inlet hopper to prevent accidents and exclude extraneous matter (paper, strings, rubber or leather pieces, etc.) from the system.
A magnet should be inserted into the system to collect metallic fragments found in mealy substances which could otherwise cause serious damage and losses in production. From the hopper, mealy substances pass through a sieving system which grades the materials into the desired particle sizes.
Horizontal sifters have the advantage that they are not damaged by pollutants, but they require a large amount of space.
Roller sifters have a small space requirement, but are often damaged by pollutants. Their screening cloths should be changed frequently.
After passing through the sifter, materials are carried to storage silos (bins) by a pneumatic conveyor. “Overs” are generally taken back to a grinder or bagged separately.
The grinder is one of the most important facilities used in manufacturing mixed feed. The grinding of ingredients generally improves feed digestibility, acceptability, mixing properties, pelletability, and increases the bulk density of some ingredients.
Grinding can be done:
Mill types used in feed manufacturing
Stone mills are the oldest type. They need a lot of maintenance and space.
Roller mills. These are used primarily in the mill industry. They produce relatively little flour and much middling. They are not used in fish feed manufacturing.
Combined mills are much used in Western Europe. In this type of mill, attrition and crushing occur.
Plate mills are mostly used in the USA. Material to be ground proceeds in a zigzag way towards the centre of plates while it is crushed.
Bolted mills are not common. Material to be ground is thrown against rotating bolts.
Beating-cross mills are similar to hammer mills (see below), but the beating elements are fixed. Their advantage is that beating elements can be changed easily. A magnet is inserted at the inlet hopper.
Hammer mills are the most widespread in mixed feed manufacturing. They are mostly impact grinders with swinging or stationary steel bars forcing ingredients against a circular screen or solid serrated section called a striking plate. Most hammer mills have a horizontal drive-shaft which suspends vertical hammers, but for some ingredients (e.g., dried animal by-products) a vertical hammer mill is more efficient. Screen mesh in hammer mills is generally 3.1–5.5 mm. In fish feed manufacturing, screens of 1–1.5 mm mesh size are used.
Materials can be classified into three groups according to their grindability:
Cereal grains are easy to grind
Springy materials (e.g., lupin) are hard to grind, especially their skins or shells
Fat, greasy ingredients (e.g., meat meal) which should generally be ground together with other materials.
Crushed, ground and sieved ingredients are placed in storage bins from where they are measured and conveyed into the mixer in the quantity defined by the feed formula. Since the aim of mixing is to render every ingredient of the mixed food (i.e., in the pellets) homogeneous, accurate weighing of ingredients is very important.
Ingredients can be weighed either in batches or continuously by a scale working automatically or manually controlled.
The latest weighing facility is controlled by a punch-card system, which stops weighing when any fault arises in the operation (e.g., wrong measuring or manual addition of premixes or medicines not done in accordance with the given formula).
From the storage bins, ingredients are carried into the scale tank by a screw conveyor equipped with several gears. Preliminary mixing of ingredients starts in the scale tank.
Requirements for the scale
It should be easy to unload. This is assisted by a vibrator and an automatic stop-valve.
The scale should weigh accurately.
The programme should be rapidly exchangeable.
The mixture of weighed ingredients enters the mixer through a flap-valve.
The homogeneity of the mixture depends on:
Types of feed mixer
Diffuse mixers. These are mixer drums or rollers in which centrifugal force is used for mixing. They generally operate continuously. Advanced versions are equipped with paddles mounted on the shaft.
Gravitational mixers. These are generally applied in the mill industry in air flow or vertical versions.
The so-called mechanical mixers are in most widespread use:
Vertical mixers may consist of a hopper-shaped container, with a single or double screw (auger) located vertically through the centre. Two types are used: (i) with a stationary screw, (ii) with a rotating screw.
Horizontal mixers. These are equipped with mixing paddles, screws, or a combination of the two. They are of counterflow type and work with a high accuracy. Mixers of the so-called “Lödige” type are worthy of special mention. In these, ploughs are spaced in a spiral around the mixer shaft. These mixers are mostly used with liquids, meat pastes, oils, fats, etc.
In fluidization mixers, ingredients are subjected to strong air flow and mechanical impact.
In mixing, both dry and liquid components (e.g., fats, molasses) are used. Liquid components improve energy content, taste and durability. These feeds can be stored in heated bins with double-panelled, insulated walls. Heating is by steam or hot water via pipelines. Ingredients are kept in tanks, and conveyed to the mixers with the help of pumps. Mixing lasts 3–5 min.
Pelleting
The most important features of fish food pellets are: resistance to abrasion, crushing strength and water stability.
The strength of the pellet is ensured by different bonds, such as:
firm chemical bonds, achieved by steaming or heating, e.g., milk powder, sugar, urea, starch, etc.
connections promoted by the interface powers of the interstitial liquid
adhesion, i.e., a capillary suction effect which occurs between two particles.
Generally a surge bin is incorporated between the mixer and the pelleting mill, from where the feed falls by gravity into the steam conditioning chamber. Thorough blending of feed and steam in the steam conditioning chamber is ensured by paddles. The conditioned feed is then fed by means of a distributor auger into the pelletizing chamber, from where it is extruded through the die. As the die rotates, feed is pressed against its inner wall by a set of three rollers. Extruded pellets of appropriate length are cut off by an assembly of knives mounted on the inside of the die casing.
Pellets coming from the mill are generally hot, soft and moist. A flow of cool air in the cooler-drier promotes evaporation of water and consequently drying of the pellet. Pellets should be cooled to ambient temperature.
Cooler-drier facilities
Vertical cooler-driers are of high capacity and need relatively little space.
The advantage of the horizontal cooler-drier is that the conveyor belt carrying the pellets moves, but the pellets themselves do not. Thus crumbling is avoided. The times necessary for drying layers of pellets 15–20 cm and 4–6 cm thick are respectively 15–20 and 5 min.
Dry pellets are then sifted and distributed according to particle size. Dust is taken back to the pellet mill, while crumbles and pellets are bagged off.
Sometimes pellets extruded through the 3–5 mm dies are too big for fry. They can then be crumbled through special rollers.
References
New, M.B. 1987 Feed and feeding of fish and shrimp: A manual on the preparation and presentation of compound feeds for shrimp and fish in aquaculture. Rome, UNDP/FAO, ADCP/REP/87/26, 275 p.
Tacon, A. 1988 The nutrition and feeding of farmed fish and shrimp. A training manual, 3 Feeding methods. Brasilia, FAO-GCP/RLA/075/ITA, Field Document 2, 208 p.
