By: Paul B. Brown*
Water, water every where Nor any drop to drink (Samuel Taylor Coleridge, 1798).
Coleridge’s quatrain from The Rime of the Ancient Mariner seemed an appropriate backdrop for this article. We live on the blue planet, life as we know it cannot exist without water, and readers of this publication work with, raise or have a general interest in animals that live in water. However, water may be the next major obstacle to further development of aquaculture. Credit must also be given to Professor Otto Doering, Purdue University, Department of Agricultural Economics for the phrase “truly wicked problem”, a phrase he used to describe the challenge of achieving sustainable food production “because it is not amenable to the traditional scientific method of problem solving.” Further, truly wicked problems have “no single solution, and there is no stopping point. There is also a higher degree of outcome uncertainty with wicked problems” (Doering, 2014. A truly wicked problem. Resource Magazine, American Society of Agricultural and Biological Engineers, November/December:23).
At first glance, water and nutrition may not appear related, particularly as we focus on aquatic organisms. However, demand for water exists within all food production systems. In aquaculture, this demand has been related to the water required to produce feed ingredients. Thus, the dietary formulation and associated water required to produce each ingredient contribute to the water foot print. The more carnivorous species in aquaculture have the lowest water footprint because dietary formulations contain a high percentage of fish meal and fish meal requires relatively little water to produce, process and distribute. Overall water footprints for mandarin fish and gilthead seabream are 88 and 500 m3/ton of fish produced, respectively (Table 1 - Pahlow et al., 2015. Increasing pressure on freshwater resources due to terrestrial feed ingredients for aquaculture production. Science of the Total Environment 536:847-857). For more omnivorous species, water footprints can be over 2000 m3/t. Commodity feed ingredients (soybean, corn, wheat, canola, groundnut, lupin, cassava, etc.) require significant water resources during their production, processing and distribution cycles and use of those ingredients in diets increases the water footprint of that species. Data presented in Table 1 reflect only the dietary water footprint; complete freshwater demands for various species and production systems have not been developed.
There is significant variability in the water footprint of common feed ingredients. Data in Table 2 are the total global average water footprints for several commonly used ingredients in aquaculture feeds. Changing dietary formulations by altering concentrations of major ingredients will alter the overall water footprint of aquaculture.
The calculation of water footprint includes consideration of the feed conversion ratio (FCR) for the target species. While overall water footprints for aquaculture species/system combinations have not been determined, the efficient conversion of ingested food to body mass in aquatic organisms might place aquaculture production in the more efficient category of water footprints for animal production. Table 3 shows values for all phases of beef, sheep, goat, pig, chicken and egg production, from birth/hatching to market. These values are not comparable to the aquaculture data in Table 1. However, these values have a similar pattern to other a comparative animal production figures, particularly those comparing feed conversion ratios for various animal species. Further work in this area will help identify those approaches that minimize the water footprint of aquaculture.
The first truly wicked problem in aquaculture nutrition was fish meal; a great ingredient, but finite supply, increased demand, resulted in increasing price. Research on alternative ingredients to fish meal began over 30 years ago and continues today. A wide range of ingredients have been evaluated in response to the fish meal dilemma and substitutions vary across the globe. This seems to fit Professor Doering’s definition of a truly wicked problem (i.e., no single solution, no stopping point, and high degree of outcome uncertainty). Attempting to solve the initial wicked problem in aquaculture nutrition may be driving us toward the next wicked problem. Water footprint is a bit broader issue than the focused fish meal issue, but one that deserves consideration in the short term.
Population increases and changing food habits are placing significant demand on food production systems. Between now and 2050, increases of 60-100% over current food production levels have been projected. The limiting resource in food production will be freshwater. Currently, food production, harvesting, processing and distribution demands approximately 70% of the total global supply of freshwater. There is not enough freshwater to realize increases in food production of 60-100% above current levels. Future food production systems will need to consider the demand for freshwater and limit its use. If the water footprint of aquaculture production and feeds becomes a significant consideration, research in this area will most likely conclude there is no one solution and the research may continue for many years into the future. The outcome of this line of research is uncertain.
Dr. Paul Brown is Professor of Fisheries and Aquatic Sciences in the Department of Forestry and Natural Resources of Purdue University. Brown has served as Associate Editor for the Progressive Fish-Culturist and the Journal of the World Aquaculture Society, among many others.