VPP 322: Aquatic Animal Diseases, Health Care and Management (1+1)

TYPES OF AQUACULTURE FEEDS

Artificial feed used in aquaculture are of the following types

• Wet feeds
• Moist feeds
• Dry feeds
• Larval feeds

Wet feeds

• Feeds containing moisture levels in the range of 45-70% are prepared from high moisture ingredients such as trash fish, fishery waste, slaughter house waste, etc. These feeds are made at the farm shed on a day-to-day basis and fed mainly to carnivorous fish such as sea bass, sea bream, eels, etc.

Moist feeds

• Moist feeds contain moisture level in the range of 25-45% and are made from a mixture of high moisture ingredients as in wet feeds, and dry pulverized ingredients. Semi-moist feeds with moisture content in the range of 15 to 25% have a minor contribution from high moisture ingredients.
• Wet, moist and semi-moist diets are considered to be more palatable to most species because of the soft consistency, and good growth and feed efficiency achieved.
• The major disadvantage of these feeds are 
  • The transportation and storage under refrigeration until use to prevent spoilage 
  • Irregular availability of fresh raw fish and other animal wastes in adequate quantities
  • Introduction of pathogens, particularly from fishery wastes, if not adequately pasteurized
  • Improper transportation and storage damage certain labile vitamins and lipids and favour propagation of fungi and bacteria in such feeds
  • Unconsumed feeds may affect the water quality.

 

Farm-made moist feed

Dry feeds

• Dry feeds contain moisture in the range 7-13%. They are relatively easy to manufacture, transport, store and convenient to dispense into the culture systems. Other advantages include bulk purchase and storage of ingredients option to select a wide variety of ingredients with specific nutritional characteristics. Dry feeds can be produced in different sizes to suit the specific needs of the larvae to specialized diets for broodstock. Dry feeds also permit production of specialized feeds such as medicated feeds incorporated with specific medicines or antibiotics required to control any disease out breaks, hormones incorporated feeds to produce monosex individuals or for growth promotion or to induce maturation in fish and prawns.
• Dry feeds may be either prepared using dry ingredients alone or a mixture of wet and dry ingredients adequately processed and dried. Dry feeds may be made as meals, pellets, granules, flakes etc.

Larval feeds 

The various types of artificial diets that have been considered for weaning larvae are:

• Minced diets
  • A feed paste is prepared by homogenizing wet or wet and dry ingredients with additions of minerals and vitamin premix and binders and fed as such.
• Wet microparticulate diets
  • A custard diet prepared with chicken eggs, prawn flesh, clams, fish solubles, vitamins, minerals, feeding stimulants and wheat flour and homogenizing to get fine particles. The desired size can be obtained by sieving.

Dry microparticulate diets

• Preparation of a water stable matrix of dry ingredients or a mixture of dry moist and wet ingredients followed by suitable drying (freeze drying, vacuum drying, oven-drying), grinding and sieving to get desired particles. This is the most widely used type of artificial diet for larval rearing.

Larval feed

• Spray dried diets
  • Well mixed finely ground materials are sprayed into air and then dried. Particles ranging in size 50-100 microns are produced and used for rearing marine fish larvae. 
• Microbound diets      
  • These are powdered diets with a binder. Carrageenan, agar, zein, alginic acid and gelatin microbound diets are produced for fishes.
• Microcoated diets
  • These diets are prepared by coating microbound diets with some materials such as zien and cholesterol-lecthin.
• Microencapsulated diets
  • The concept of a miniature packaging assemble (a microcapsule) in which liquids or particulate dietary components are enclosed in a carefully engineered wall, which release under specific macro or microenvironmetnal conditions has broad application in fish culture. Release of the internal nutrient components at active sites can be accomplished by rupture (enzymatic). The capsulated environment thus minimizing organic load in the system and alteration in oxygen and pH levels. The capsules can be produced in a range of sizes that can be offered to the fish larvae and fry as they grow. Depending upon the capsules wall material, nylon protein microencapuslated diet (MED), gelatin gum acacia MED, egg albumin Med, glycopeptide and chitosan MED.
• Flake diets
  • Flake diets prepared through a double drum dryer processing unit is a potential feed for fish. Flakes can be reduced to small particle sizes by grinding and sieving without reducing the basic stability characteristics. Ingestion rates of the feed could be enhanced by using suitable binders, flavours and colours.

Flake food for fish larva

FEEDING STRATEGIES

• In order to achieve maximum growth and best feed efficiency of a given feed from a culture system the feeding strategies employed, feeding rate, feeding level, feeding frequency and feeding methods are extremely important.

Feeding rate

• The amount of feed offered (ration size) should be regulated with reference to the biomass of the fish or prawns being cultured, as well as observations on their daily feed intake. Normally farmers, without considering the feed intake of the fish, supply feed according to the biomass. This often leads to over-feeding, feed wastage and deterioration in water quality, resulting in poor production and FCR (Food conversion ratio).
• Daily observation on feed intake in check nets or trays for prawns is very important to decide on the amount of feed to be offered on subsequent days. Factors that may affect feed intake are poor water quality, low oxygen level, high temperature, high ammonia, nitrite and hydrogen sulphide levels, toxic metabolites, over sized or undersized feed particles and deterioration in health of the animals.
• Fish fry and fingerlings, and prawn post-larvae and juveniles require more food to meet the demand for fast growth so the ration size should be adjusted accordingly.
• Both over feeding and underfeeding affect growth, production and FCR. The daily feeding rate for prawn (% of biomass) varies from 25% to 2% during the crop period, maximum during the post larval stage (PL20) to the minimum when the animals reach marketable size. Feeding at constant rate should be avoided.

Feeding frequency

• The number of meals offered daily and time of feeding are also factors that affect growth and feed efficiency. Frequent feeding reduces starvation and stunting, enables uniform growth and results in minimum feed wastage.
• In the case of fish, the daily ration or the total amount of feed fed per day per pond cage etc. of feed is offered in several meals often 4 to 6 times a day and as the fish grow. the number of meals are reduced either one or two. Feeding of finfish is mostly done during the day, between 6 AM and 2 PM, but during fry stage a continuous feed supply is maintained.
• In the case of shrimp the number of meals offered per day range from 4 to 6 for post larvae and juveniles, to 3-6 times a day for sub-adults and adults. The total amount of feed to be offered each day is divided into small quantities and fed. 

Size of the feed

• Properly sized feeds must be fed to satisfy the specific demands of the growing stages. If a particular feed contains under sized or over sized particles, screening should be done to remove such feed particles. Dust or fine particles if present often clog the gills of the fish and shrimp and cause damage to the gills.
• Clogging of gills by feed dust also provides a substrate for propagation of a variety of microorganisms which cause further damage to the animal. The wasted feed particles also pollute the water.
• Every individual in the cultured population must obtain a share of the feed offered at every meal time (time of feeding). So the number of feed particles in the daily ration should atleast correspond to the estimated number of surviving individuals. Thus artificial feeds must have adequate number of particles to satisfy almost the entire surviving population.
• Feeding method also should ensure that each of the cultured organism gets a share of the feed being supplied. Dry pellets, granules and crumbles for fish and shrimp could be broadcasted. Fish in general are fast feeders and good palatable feeds are consumed within 15-30 minutes by most species. But shrimp being slow feeders it is necessary to evenly distribute granles and pellets. Broadcasting the feeds from pond bunds is quite adequate for small ponds (<0.5 ha). But in larger ponds (>0.5 ha) broadcasting the feeds from bunds should be supplemented by distribution in slightly interior areas using a small boat.
• Moist dough feed and meals should not be broadcasted; but kept in earthen or plastic trays placed in the peripheral areas of the pond bottom. Adequate number of feeding trays (30 – 40 \ha) must be used to create maximum opportunities for the shrimp to feed.
• Feeding method adopted in semi intensive carp culture system in Andhra Pradesh in quite unique and the same could be adopted in the carp farming states. The outline of the method is as follows: Feed mixture, de-oiled rice bran mixed with either groundnut oil cake, cotton seed cake, mustard cake or sunflower oil cake often in the ration 3 - 4:1 is kept in perforated fertilizer bags tied to bamboo or casuarina poles. About 20 - 30 bags are used per hectare. Feed mixture is transported in a catamaran or a small raft and equally distributed in the feedings bags. Fish browse on the feed through the perforations in the bags and within two hours most of the feed kept in the bags is consumed
• The efficiency of the feed is measured by the amount of feed necessary to produce a unit weight of fish. This is called as Food conversion ratio or FCR which is the unit weight of feed given, divided by the live weight (or wet weight) of animal produced.

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