In this section the feeding methods or options available to the fish or shrimp farmer are first briefly described and guidelines presented so as to assist the farmer to choose his or her own aquaculture feeding strategy.
The food and feeding of farmed fish and shrimp can be viewed at four basic levels of refinement or input (Tacon, 1986):
Basic rearing system where fish/shrimp growth is totally dependent upon the consumption of live food organisms and plants naturally present within the water body. Fish/shrimp growth will therefore vary depending on the natural productivity of the water body and the density and total biomass of the cultured species present; fish/shrimp growth increasing with increasing natural productivity and decreasing stocking density. This feeding strategy is generally employed within extensive pond farming systems with low fish/shrimp stocking densities.
Here, chemical and /or organic compounds (termed ‘fertilizers’) are externally applied to the water body containing the cultured fish or shrimp so as to increase the production of live food organisms and plants naturally present, and so increasing the fish/shrimp production capacity of the culture system; fertilizers serving primarily as a direct source of essential nutrients for the resident natural food chain within the water body. Organic ferilizers are used here to include animal manures (applied by hand or through livestock integration), green manures (fresh plant cuttings), and fresh or composted agricultural by-products. This feeding strategy is typical of extensive and semi-intensive farming systems.
When fish/shrimp stocking density and standing crop is such that the natural productivity of the water body alone cannot sustain adequate fish or shrimp growth, an exogenous supplementary diet can also be fed as a direct ‘supplementary’ source of dietary nutrients for the cultured fish or shrimp; the dietary nutrient requirements of the cultured fish or shrimp species being supplied by a combination of natural live food organisms and supplementary diet feeding. Supplementary feeds usually consist of low-cost agricultural/animal by-products, and may involve the use of a single food item in its fresh or unground state (ie. such as mill sweepings, beer waste or rice bran) or the use of a combination of different feed items in the form of a feed mash or pellet. Although supplementary feeds are used as a direct source of dietary nutrients for the farmed species, when used in excess these products may also exert a fertilization effect on the water body. With this feeding strategy higher fish and shrimp stocking densities are possible and consequently higher fish/shrimp yield per unit area. This feeding strategy is typical of a semi-intensive farming system.
In contrast to the previous feeding strategies, complete diet feeding involves the external provision of a nutritionally ‘complete’ high quality diet containing a predetermined nutrient profile. 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 approximates to the known dietary nutrient requirements of the fish or shrimp species in question under conditions of 'maximal' growth. Alternatively, complete diets may consist of a single food item of high nutrient value (ie. trash fish, cultured live food organisms - Artemia nauplii), or a combination of both. In view of the high fish/shrimp stocking densities generally employed with this feeding strategy, no nutritional benefit is assumed to be gained by the cultured fish or shrimp from natural food organisms present within the water body. This feeding strategy is typical of an intensive culture system.
A prerequisite to the selection of appropriate fertilizers and feeds for use within an aquaculture feeding strategy is first to conduct a survey of the fertilizer and agricultural feed resources of the area, district, state or country in question, where these resources are geographically located, how much is available and when, who is currently using this resource and how, and the composition and cost of these resources at source and with transportation. Guidelines for conducting a National Agricultural Feed Survey (NAFS) have been presented in a separate report (Tacon, Maciocci and Vinatea, 1987).
In addition, many important economical, sociological, biological and environmental factors will have to be considered by the farmer before choosing an appropriate fertilization, supplementary diet or complete diet feeding strategy, including:
Market value of fish/shrimp species to be farmed
Financial resources of the farmer - amount of capital available for investment
Farming traditions, ‘taboos’, and managerial ability of the farmer
Time available for the farming activity - full or part-time farming activity
Labour availability, training requirement and cost
Service availability and cost - electricity, gas, water, fuel
Fertilizer and/or feed availability and cost
Fertilizer and/or feed transport and processing cost
Feeding habit of fish/shrimp species to be farmed - carnivore, omnivore or herbivore
Feeding behaviour and nutrient requirements of fish/shrimp species to be farmed
Water quality requirements of fish/shrimp species to be farmed - oxygen, temperature, salinity, ammonia, pH, suspended solids
Intended production unit - lagoon, pen enclosure, cage, raceway, tank, earthen pond
Intended fish/shrimp stocking density for all stages of the culture cycle
Water exchange rate within intended production unit
Natural productivity of the water body
Food and feeding cost/unit of production/unit time
Fixed and non-food cost/unit of production/unit time
However, the relative importance or value (if at all) of these factors will depend, inturn, on whether the proposed farming activity envisaged is geared toward a subsistence/home comsumption farming activity, a commercial/market cash-income farming activity, or a combination of both.
The aim of a subsistence rural farming activity is to produce fish or shrimp for home consumption using locally available resources at minimum cost. The intended production unit is usually regarded as consisting of a single 100 m2 earthen pond owned or operated by one or more family units. Here, the farming activity conducted is usually on a part-time basis, with very limited cash funds being available for pond construction and the purchase of fry, fertilizers, feeds or farm equipment. Given the above constraints the farmer is faced with the culture of fish or shrimp species which require little or no daily management, are tolerant of often poor water quality conditions, and species which feed low on the aquatic food chain and so can make maximum use of natural pond food organisms and low grade agricultural by-products. Rural farming activities are therefore generally restricted to the culture of herbivorous or omnivorous fish/shrimp species within semi-intensive or extensive pond conditions.
On the basis of these farming restrictions it is clear that the feeding strategy to be implemented must be of minimum or no cost to the farmer, is simple to operate and manage, and requires only part-time labour inputs. Of the four basic feeding strategies listed (1.1.1 - 1.1.4) it is believed that the most appropriate at the village or subsistence level is a low cost semi-intensive feeding strategy using a combination of pond fertilization with organic manures (either by direct application or composting, or through integration with livestock) and supplementary diet feeding with agricultural by-products. This feeding strategy will have the necessary flexibility in that fish/ shrimp growth is not dependent on a single food source but on a combination of different feed types (ie. natural live pond food organisms and artificial supplementary feeds). It is essential that the feeding strategy chosen has this flexibility as fertilizer, feed and labour inputs may vary over the growing season depending on availability and the financial status of the farmer.
The aim of a commercial cash-income farming activity is to produce fish or shrimp for cash sale at maximum profit. Here the most important criteria is the market value and demand of the fish or shrimp species to be farmed; the market value dictating the profit margin relative to production costs, including the cost of feeding.
Commercial cash-income farming activities can be of an extensive, semi-intensive or intensive nature, either within lagoons, pen enclosures, ponds, cages, concrete tanks or raceways. Generally the farming activity involves full-time labour inputs and a high initial capital outlay. The feeding strategies employed vary with geographical location, the production unit used, and the fish or shrimp species farmed. All of the previously mentioned feeding strategies (1.1.1 - 1.1.4) have and are currently being used within commercial aquaculture enterprises.
