Mr. A. G. J. TACON
INTRODUCTION
In Contrast to extensive and semi-intensive farming systems where fish derive all or a substantial part of their nutrient needs from naturally available food organisma, fish maintained under intersive culture conditions are totally dependent on the external provision of a nutritionally “complete” diet throughout their culture cycle. Traditionally, “complete” diets have taken the form of a dry or moist pelleted feed consisting of a combination of different feed ingredients, the overall nutrient profile of which, as near as possible, approximates to the nutrient requirements of the fish species in question under conditions of “maximal” growth. Alternatively, complete diets may consist of a single food item of high nutrient value (i. e. trash fish, live food organisms - Artemia), or a combination of both.
For the majority of merine farmed fish, there is scant information on basic nutrient requirements. This is in sharp contrast to the intensive poultry or trout industry, where basic dietary requirements for protein, essential aminoacids, essential fatty acids, vitamins and minerals are well established. At present, these shortcomings are overcome by using fresh or frozen fish/dry compound feed combinations with a high inherent nutrient safety factor; the use of which being economically justified with good management by the high market value of the farmed species (i.e. sea bass, gilthead bream, turbot, sole, eel).
FEEDING PRINCIPLES AND GUIDELINES
From a nutritional viewpoint, the principle governing the feeling of fish under intensive culture can be viewed as follows:
That the food given is palatable and consumed completely with minimum effort and wastage.
That the nutrient profile of the food given approximates as far as possible to the known dietary nutrient requirements of the fish species in question.
That the food is digestible, keeping the fish healthy and growing normally.
Ideally, that the food is efficiently converted into body tissue in the form of fish growth (i. e. optimal feed conversion efficiency).
In practice, however, from a commercial farming viewpoint, the choice of a particular feeding strategy is based on an assessment of three basic criteria (for intensive culture):
Feed availability and handling.
Feed performance.
Food and feeding cost/unit of production/unit time and the rate of return on capital.
For example, four basic hatchery feeding strategies are currently available for the mass rearing of marine fish larvae from first feeding, through metamorphosis, to the post-larval stage. These include:
The exclusive use of a succession of live planktonic food organisms (i. e, algae, diatoms, flagellates, yeasts, rotifers and Artemia salina nauplii).
Use of selected live and/or frozen plankton in conjunction with “fresh” and/or frozen Fish, mollusc or crustacean tissue.
Use of selected live and/or frozen plankton in conjunction with dry feed materials or formulated diets.
Exclusive use of microencapsulated or microparticulate larval diets.
Using the guidelines listed above, each hatchery feeding stratagy can be assessed as follows:
FEED AVAILABILITY AND HANDLING
A - LIVE PLANKTONIC FOOD PRODUCTION
Source of culture organisms
Local
Species available
seasonlity
personnel requirement for collection
Imported
Dependability of supplier
minimum quantity of order
lead time on orders
variability in performance (hatchability - Artemia cysts)
import restriction - licence/tax/country
Maintenance and production of culture organisms
Stock cultures
Space requirement - laboratury/phytolaboratory
personal requirement - specialized training
service requirements - power/light/gas/air/UV/aircon - backup
culture media requirement - inorganic salts/trace elements/vitamins/chelating agents/antibiotics
equipment requirement - autoclave/filters/glassware/microscope/cell counter/plankton culture vessels
Production cultures
Extensive continuous culture (green water system) requirements -fertilizers/personnel/air supply/space/tanks - backup
Intensive batch culture system requirements - space/air and CO 2/supply/personnel/fertilization/UV and light/plankton culture vessels/phytolaboratory.
Survival/stability
Survival/shelf life of stock cultures
survival of production culture - frequency of culture failures
necessity to keep stock cultures all year round
B. FISH, CLAM OR CRUSTACEAN TISSUS FEEDING OPTION
Sources
Fisherman
Processors
Farm staff/hired labour
Quality
Species available
Forms available
whole
heads, tails, skin bone
offal
Handling at source
icing
freezing
boxing
salting
storage
Handling/processing on site
Service requirement - electricity/gas/air/water - backup
equipment requirement - mincing/blending/sieving/boiler
personnel requirement
storage requirement - space/freezer/refrigerator
depandability of services - power supply/backup
Nutrient content
proximate composition
particle size requirements
seasonal variations in nutrient content
possible contaminants/anti - nutritional factors
spoilage characteristics/storage life
Larval feeding requirements
manual feeding - feeding regime
automatic feeders
service requirements - electricity/air
personnel requirements for feed preparation/feeding - man/hours/day
Quantities available
Daily basis
Weekly basis
Seasonality
Dependability of supplier
Alternative species available
Transport requirements for feed delivery to hatchery
Minimum quantity of order
IN HOUSE PRODUCTION OF A DRY/MOIST DIET
Feed ingredient availability
Local sources
nutrient content
variability in composition
seasonality
particle size
possible contaminants/antinutritional factors
processing/cooking requirements
spoilage characteristics/storage life
storage requirements - space/refrigeration
dependability of supplier
minimum quantity of order
Imported ingredients
nutrient content
variability in composition
seasonality
particle size
possible contaminants/anti-nutritional factors
processing/cooking requirements
spoilage characteristics/storage life
storage requirements - space/refrigeration
dependability of supplier
minimum quantity of order
lead time on orders
import restrictions
Feed preparation and handling
Power requirement
electricity/gas/petroleum/steam
dependability of power supply - backup
water requirement
Personnel requirement - man hours/day
Feed preparation space requirement
Feed processing equipment requirement - grinder/hammermill/blender/mixer/extruder/pelleter/freeze drier/solar drier/air drier/oven
Larval feeding requirements
manual feeding - feeding regime
automatic feeders
service requirements - electricity/air
Feed storage
Shelf life/stability
Freezing/refrigeration requirement
Packing
Maximum storage capacity
Minimum production batch
D. IMPORTATION OF MICROENCAPSULATED/MICROPARTICULATE LARVAL DIET
Sources
Japan, Taiwan, S.E., Asia, U.S. Europe
Quantities available
Dependability of supplier
Minimum quantity of order
Lead time on orders
Quality
Nutrient content
proximate composition
particle size distribution
stability in water
variability in composition
spoilage characteristics
Larval feeding requirements
manual feeding - feeding regime
automatic feeders
personnel requirement - man hours/day
Storage
Storage space requirement
Power supply requirement - electricity/gas/petrol
refrigerator
freezer
dependability of power supply - backup
Packing and shelf life of feed
FEED PERFORMANCE
Behaviour of feed in water
Buoyancy
Aggregation/dispersion characteristics
Stability/leaching characteristics
rate of nutrient loss
effect on water quality
inducement of algal/bacterial growth/contamination
Swimming behaviour of planktonic food organisms
Feed requirement for each critical growth phase
mg/larvae/day
food density/larvea/day
particle size requirement
Larval development
Feed days required for each growth phase
Feeding behaviour of larvae
Distribution within culture tank
even distribution
clumping/aggregation
surface/mid-water/bottom
ability to capture prey/feed particles
Feeding incidence of larval population (%)
Visibility of faecal strands
Feed palatability/attack response
Abnormal swimming behaviour
Incidence of cannibalism
Larval survival
Mean survival rate (%) for each critical growth phase
Frequency of mass larval mortalities - batch failures
Incidence of bacterial/parasitic infections related to poor water quality resulting from poor diet stability
Incidence of larval deformities
scoliosis/lordosis
Short body dwarfism
Tissue wasting disease
moulting capacity (shrimp)
frequency size distribution
Additional hatchery service requirement related to feeding option used
Water exchange (%) frequency
Aeration
Lighting
Tank cleaning
Water sterilization
Use of antibiotics
FOOD AND FEEDING COST/UNIT OF PRODUCTION/UNIT TIME
Capital (fixed costs related to feeding option) 1
Land - total hatchery area devoted to live production, feed preparation and storage
Structures - shed, store, laboratory, tanks, etc… devoted entirely to live food production, feed preparation and storage.
Machinery/equipement - pelletizer, grinder, feed dispensers, blender, boiler, silos, oven; freeze drier, autoclave, refrigerator, freezer, pumps, filters, microscope, air conditioner, mincer, sieves, etc… directly associated with feeding option.
Operating (variable) costs related to feeding option
Personnel - (manpower requirement, including level of technical skill required)
Energy - (electricity, fuel, oil)
Feed procurement, handling (delivery), storage and processing cost. Additional factors which may also have to be taken into consideration include import duties/taxes, minimum quantity of order, availability of foreign exchange/credit facilities. A crude estimate can be made of feed costs/unit of fish produced using these values.
Maintenance/spares
Fertilizers and chemicals
General supplies and materials
Miscellaneous
Market value of fish and revenue from sales/year
Total cash outlay of hatchery/year (includes hatchery operating costs, sinking fund and insurance, etc…)
Cash outlay/106 larvae produced/unit time
Net income (before taxes, 3–4)
Income over total outlay (%)
SPECIFIC DIFFICULTIES ASSOGIATED WITH THE FEEDING OF MARINE FISH
1. Live food requirement during first feeding
The majority of marine farmed fish have small diameter eggs (1 – 2 mm) producing small larvae ( 0 5 – 1 5 mg wet weight) with poor yolk sac reserves. For some species, the hatchlings are so poorly developed that their mouth is still closed and gastro-intestinal tract non-functional (i.e. gilthead bream). In addition, after a short yolk-sac abdorption period, larvae are often incapable of consuming feed particles 50 m. Bearing these factors in mind, therefore, and the problems associated with diet stability and nutrient leaching, it is perhaps not suprising that most commercial hatchery rely on the use of live food organisms (commonly Brachionus plicatilis and Artemia salina for the first feeding larvae until metamorphis is complete. Despite the economic efficacy of a well managed marine fish hatchery using a live food feeding regime, there are numerous disadvantages associated with a live food feeding stratagy, including:
High initial capital investment costs - fabrication of expensive and sophisticated live food production facilities, including laboratory with high energy service requirements.
Land/space requirement - valuable hatchery space, which may otherwise be used for larval production, is devoted to live food production.
Stock culture maintenance requirement - feeding regimes involving the use of pure diatom/algal species and specific rotifer strains necessitate the maintenance of stock cultures on a yearly basis; usually requiring the construction of an air conditioned laboratory for this purpose.
Labour requirement - The maintenance and production of live food organisms necissates a high labour (skilled) requirement of live food production units does not favour the development of small scale hatcheries by the traditional farmer with limited cash funds.
Small scale hatchery development - the current high capital investment costs and high labour (skilled) requirement of live food production units does not favour the development of small scale hatcheries by the traditional farmer with limited cash funds.
Weather effect - The production of live food organisms in outdoor tanks is affected by the climatic conditions, resulting in variable larval survival, depending on the season.
Variable quality and nutritive value - The quality and nutritive value of live food organisms is variable depending on strain, source and culture method used (WATANABE et al., 1983).
Availability and cost - On the basis of culture techniques used at the Centre Océanographique de Bretagne (France), the dry weight cost of Artemia nauplii and rotifer Brachionus spp has been estimated to be US $ 220/kg and US, $ 2000/kg respectively (GIRIn, 1977). Similarly, in many developing countries, the importation of Artemia cysts necessitates important clearances, taxes and the availability of foreign exchange facilities.
Bearing these factors in mind, it is essential that a simple and inexpensive artificial feeding package be developed if intensive marine farming systems are to be realized by the traditional fish farmer.
2. Feeding behaviour and diet stability
Maximum benefit from feeding can only be achieved if the food provided is ingested by the fish. An understanding of the feeding behaviour of the fish is, therefore, essential. The diet presented must have the correct texture, particle size, density (buoyancy) and attractiveness to elicit an optimal feed response. Marine fish, and especially their larvae, appear to be particularly exacting in this respect. For example, although marine fish held in captivity generally rely on sight to locate their food, they also rely on chemoreceptors located in the mouth or externally appendages such as lips, barbels and fins. Consequently, with many marine fish species food particles are carefully sensed before being taken into the mouth ;the presence of feeding attractants within the food acting as ingestion stimulants.
Feed palatability and feeding attractants: At its lowest level the often poor palatability of a hard dry pelleted diet can be improved simply by adding 10–20% water so as to give a soft pellet texture(1.e. flat fish). For many marine fish species specific dietary feeding attractants have been found to elicit a feeding response under captive conditions, including the nucleosideinosine and inosine-5-monophosphate (for turbot, MACKIE and ADRON, 1978; PERSON Le RUYET et al., 1983) and the quaternary amine-betaïne, either alone (for 50 g. sole, MACKIE et al., 1980), or in combination with free L. amino acids and inosine (sole; MACKIE et al., 1980, CADENA ROA et al., 1982; METAILLER et al., 1983). The practical importance of feed attractants and diet palatability is particularly critical during the weaning of marine fish larvae from a live to a non-living diet. Similarly, as attempts are made to replace the fishmeal component of practical fish feed with unconventional protein sources of an alien nature to the fish (for example soybean meal), the problem of diet texture and palatability will become even greater. Finally, by improving feed palatability, the period of time the feed remains in water can be reduced, thus minimizing nutrient leaching.
Feed stability and nutrient leaching: Since many marine fish species have a slow feeding behaviour, in that they “sence” their food prior to ingestion, diet stability and consequent leaching of water soluble nutrients poses a major hazard. Nowhere is nutrient leaching more of a hazard than in diets for larval fish where mouth size necessities the use of food particles with a very high surface area/volume ratio. For example, GRABNER et al.,1981, reported the loss through leaching of almost all the free, and about one-third of the free plus protein bound amino acids from frozen or freeze-dried zooplankton (Artemia salina and moina, sp. )after a 10 minutes water immersion period at 9° C. SLINGER et al., 1979, reports the loss through leaching of up to 50–70% in vitamin C, 5–20% loss in pantothenic acid, 0–27% loss in folic acid, 0–17% loss in thiamine and a 3–13% loss in pyridoxine activity through in leaching, after a 10 second water immersion period (1, 18–2, 36mm diameter trout pellet). Similar water stability tests with complete diets for penaeid shrimps report water soluble vitamin losses of 97% (thiamine), 94% (pantothenic acid),93% (pyriodoxine), 90% (vitamin C), 86% (riboflavine), 50% (inositol), and 45%(choline) after a one hour immersion period in sea water (CUZON et al., 1982). Although to certain extent these effects can be minimised by using dietary feeding attractants and short feeding intervals (i.e. regular feeding), various microencapsulation and microbinding stabilization techniques have recently been introduced for the manufacture of artificial diets to overcome these problems. Although it is not the intention of this discussion paper to review to these techniques here, the use of extrusion cooking techniques to produce expanded and rehydratable water stable feeds seems particularly promision (MELCION et al., 1983; CADENA ROA et al., 1982). The combination of extrusion cooking techniques with the subsequent application of a lipid-vitamin emulsion onto the outside of the expanded feed may be particularly profitable avenue for research. The advantages and disadvantages of producing an extruded diet are shown in Table 1.
3. Dietary protein requirement
The majority of marine fish species examined to date are carnivorous in feeding habit, and consequently have a high dietary requirement for protein (minimum of 40–50% on a dry weight basis) and a low tolerance for dietary carbohydrates (TACON and COWEY, 1985). At present, high quality fish meals supply the major proportion of the protein component within complete diets for marine fish, with levels of up to 70 % (of the total diet) being used within some starter rations. In view of the high market cost of good quality fish meals, it is not surprising that feed costs may account for 40 – 50 % of the total operating cost of the farming operation. Apart from being an expensive feed commodity, and of uncertain supply within the next decade, the utilization of high quality fish meals for fish feeding is also inefficient in terms of our utilization of sea fishery stocks. Clearly, alternative and ideally less expensive sources of good quality protein must be found (for review see TACON and JACKSON, 1984).
Table 1 - Disadvantages and Advantages of Extrusion cooking
DISADVANTAGES
Expansion processing requires more expensive equipment than straight pelleting (including steam pelleting).
Process requires higher pressure, steam addition and mixture temperatures.
Reduced production rates, despite a very high power (energy/electricity) requirement.
Resulting pellets requires further drying to reduce moisture content.
Higher vitamin supplement (destruction of heat liable vitamins).
Altered feed ingredients - particularly the use of feedstuffs with a high starch content.
Risk of over expansion - excessive bulkiness.
Reduced voluntary feed intake by fish.
Added cost of above to feed (10 -20% of total value).
Possibility of maillard-type reaction occuring and reducing the biological availability of specific amino-acids.
ADVANTAGES
Allows feeder to observe fish - particularly under conditions of poor visibility (if an expanded “floating” feed is produced).
Ingredients are cooked which gelatinize the starch, resulting in strong intermolecular bonding.
Pellets are more durable and have superior water stability (reduced leaching of water soluble nutrients).
Increased biovailability and disgestion of carbohydrates (higher digestible energy content).
Better feed conversion efficiency.
Delayed gastric evacuation.
Faeces are coarse and lumpy (as compared to fine and watery with steam pelleted diets).
Less dust with expanded feeds.
Reduced feed wastage - incorrectly adjusted feeders - no over-feeding.
Lower feeding rate.
Floating properly - allows determination of food consumption
Facilities water and/or oil absorption so as to produce a rehydratable semi-moist diet (larval applications) or a high lipid diet (for use at low water temperatures, or with carnivorous fish species with a low carbohydrate tolerance).
REFERENCES
CADENA ROA , M., (1982) C. HUELVAN, Y. LE BORGNE and R. METAILLER.Use of rehydratable extrued pellets and attractive substances for the weaning of sole (solea vulgaris). J.World Maricult. Soc., 13; 246 – 253
CUZON G., 1982 M. Hew and D.COGNIE. Time lag effects of feeding on growth of juvenile shrimp Penaeus japonicus (Bate). Aquaculture, 29; 33 – 44
GRABNER M., 1981 W. WIESER and R. LACKNER. The suitability of frozen and freeze dried, zooplankton as food for fish for fish larvae; biochemical test program. Aquaculture, 26; 85 – 94
MACKIE A.M. and J.W. ADRON. Identification of inosine and inosine -5' - monophosphate as the gustatory feeding stimulants for the turbot, Scophthalmus maximus. Comp. Biochem. Physiol., A60; 79 – 83
MACKIE A.M., 1980 J.W. ADSROn and P.T.GRANt. Chemical nature of feeding stimulants for the juvenile Dover sole Solea solea (L) J. Fish. Biol., 16; 701 – 708
METAILLER J.P., 1983 J. GUILLAUME, J. MEHU, R. METALLIER and G. CUZON. Preparation by extrusion cooking of improve feeds for marine animals. Proceedings “Cost 91” Extrusion Cooking, Athens, 14 – 18 November 1983 (In press).
PERSON - LE RUYET J, B. MENU, M. CADENA ROA and R. METAILLER. 1983 Use of expended pellets supplemented with attractive chemical substances for the weaning of turbot (Scophthalmus maximus). J. World Maricult. Soc.14; 67 – 678
SLINGER A.G.J., 1979 A. RAZZAQUE and C.Y. CHO. Effect of feeding processing leaching on the loss of certain vitamins on fish diets. In Finish nutrition and fish feed technology edited by J.E. HALVERR and K.TIEWS. Schr. Bundesforschungsanst. Fisch. Hamb.; (14/15) Vol. 2; 425 – 434
TACON A.G.J. and C.B. COWEY. 1985 Protein and amino acid requirements. In Fish Energetics - new perspectives (P. Calow and P. Tytler, eds). Croom Helm Press Ltd. London, pp, 155 – 183.
TACON A.G.J. and A.J. JACKSON. Utilisation of conventional and unconventional protein sources in practical fish feeds - A review. International Symposium on “Nutrition and feeding in Fish” 10 – 13 July 1984, Aberdeen, Academic Press, London (In press).
WATANABE T., 1983 C. KITAJIMA and S. FUJITA. Nutritional value of live organisms used in japan for mass propagation of fish. A review. Aquaculture, 34; 115 – 143.
