Application of nutrient requirement data under practical conditions: special problems of intensive and semi-intensive fish farming systems

Abstract

Methodological approaches for undertaking research on the dietary nutrient requirements of farmed fish should ensure that the studies are designed and conducted in such a manner that the ensuing results can be applied under practical farming conditions. Sadly, the majority of studies to date, and in particular those for omnivorous warm water fish species, have had little or no practical applicability; the bulk of nutrient requirement studies having been conducted under controlled artificial laboratory conditions. Despite the fact that silver carp (Hypophthalmichthys molitrix), common carp (Cyprinus carpio), grass carp (Ctenopharyngodon idella), bighead carp (Hypophthalmichthys nobilis) and milkfish (Chanos chanos) are the top five most cultivated fish species in the world (total aquaculture production of these fish species in 1990 totalled 4.8 million metric tonnes or 57% of the total world farmed finfish production), little or no information exists concerning their dietary nutrient requirements under practical semi-intensive pond farming conditions. To a large extent this has been due to the reluctance of the conventional laboratory-based fish nutritionist to work under applied field conditions and the difficulty of quantifying the contribution of natural food organisms in the overall nutritional budget of pond raised fish. If meaningful conclusions are to be drawn from nutrient requirement studies it is essential that the experimental fish be reared under conditions mimicking as far as possible those of the intended farm production unit and environment, including holding facility (indoor or outdoor tank, cage or pond), feed preparation technique (grinding, pelleting, drying; diet texture, form, shape, size, buoyancy and water stability), feeding method (hand, demand or automatic feeding; feeding frequency and feeding rate - fixed or satiation feeding), water quality (temperature, turbidity, salinity, oxygen and mineral concentration; water exchange rate, water circulation pattern and artificial aeration), photoperiod (artificial or natural) and fish stocking density. Finally, but not least, it is essential that the growth performance of the experimental fish be at least equal to or greater than that of the target fish species under practical farming conditions so that dietary nutrient requirements can be ascertained under conditions of maximum attainable growth.