Nutritional Strategies to Reduce Nutrient Losses in Intensive Aquaculture

Resumen

Expansion of aquaculture production is largely the result of intensification of farming activities with
a higher degree of feed input and waste output per rearing system. Concerns about the effects of
waste output on the quality of receiving water systems have led to efforts to lower levels of
enriching nutrients in discharge water. Since the enriching nutrients originate in feed added to the
rearing systems, efforts to reduce levels in farm effluents must begin with feed. Phosphorus,
nitrogen and fecal solids in farm effluent water are the “pollutants” of concern. Strategies to lower
their concentrations in farm effluent water focus on decreasing the amount of uneaten feed, and on
increasing the retention of dietary phosphorus and nitrogen by the fish. Modifying feeding levels
and methods, plus increasing pellet water stability, are the approaches used to reduce waste from
uneaten feed. Reducing phosphorus levels in farm effluents requires effort in three areas, e.g.,
information on the bioavailability of phosphorus in feeds and feed ingredients, accurate estimations
of requirements for phosphorus at various life-history stages, and formulation of feeds to match as
closely as is practical the available phosphorus level in the feed to the requirement of the fish or
shrimp. Reducing nitrogen levels in farm effluents involves the development of feeds that support
high percentages of nitrogen (protein) retention by the farmed fish or shrimp. Another nutritional
strategy useful in lowering nutrient levels in farm discharge waters is phase feeding, involving the
use of diets containing sub-optimal levels of phosphorus or protein during the final grow-out phase.
Using appropriate nutritional strategies, levels of enriching nutrients in farm effluents can be
significantly reduced without lowering fish performance or farm profitability.