The organic aquaculture movement: a role for NuPro™ as an alternative protein source

Due to its high palatability and digestibility, as well as its balanced amino acid profile, the aquaculture industry has relied heavily upon fish meal as a major component of aquafeeds; especially for the culture of higher level carnivores, such as the salmonids and certain marine finfish (Hardy, 1999). Global fish meal supplies have remained stable for the past 15 years at approximately 7 million metric tons (mmt) (Tidwell and Allen, 2001; New and Wijkstrom, 2002). But, rather than showing signs of increasing, fish meal production is declining or, at best, remaining stable. This is because many of the fish stocks utilized by the fish meal industry are either at maximum sustainable yields or over-exploited (FAO, 2002).

Due to the stability of fish meal supply, market forces have acted to reallocate the use of this commodity between competing production systems (poultry, swine, beef cattle and aquaculture; Tidwell and Allan, 2001). However, various pressure groups have recently questioned the use of fish meal in aquafeeds on ethical grounds. This has forced the feed industry to more seriously examine the use of alternate protein sources during the formulation process. Successful substitution of fish meal with more sustainable proteins could act to limit or eliminate the aquafeed industry’s dependence upon uncertain fish meal supplies; even though this industry actually represents a more economical and environmentally friendly use of the commodity because fish are more efficient feed converters than other primary users – the chicken and livestock industries.

Regardless, the aquaculture industry must move away from its reliance upon fish meal in aquafeed formulations for several reasons, bad press and attention notwithstanding. Fish meal is a relatively stable commodity, and as such, with increasing demands and stagnant supplies, prices are sure to increase substantially in the coming years (Hardy and Tacon, 2002). This scenario has been referred to as the ‘fish meal trap’ in that with current technologies and a limited supply of fish meal and oil, the continued expansion of some sectors of the aquaculture industry will steadily decline, if not cease operations altogether, due to the increasing price of fish meal (New and Wijkston, 2002).

Of course, numerous assumptions and assertions have been made in the conception of this scenario, but many of these have been verified by data from the world’s capture fisheries, as well as the predictions of the rapid growth of the aquaculture industry. Secondly, fish oil is complementary to fish meal in terms of availability and demand. The aquaculture industry currently utilizes approximately 36% of the world supply of fish oil, about 0.4 mmt (Brown and Smith, 2002). The fish oil situation is more problematic for the culture of marine carnivores, which require the n-3 highly unsaturated fatty acids (HUFA) that are major constituents of marine fish oils. Because of this requirement for n-3 HUFA, replacement of fish oil in aquafeeds for marine carnivores will prove to be difficult, but not impossible.

Finally, the move towards organic aquaculture production will provide another impetus for the industry to retreat from its present dependence upon these marine resources due to the problems they cause in the certification process.

While fish meal use is permitted in the organic standards for the European Union (EU), it must be from a certified sustainable stock, or derived from scraps of fish destined for human consumption. Currently, standards for organic aquaculture certification in the US are unprepared. However, guidelines are being discussed and they are sure to be at least as stringent regarding fish meal utilization as the EU standards, if not more so.

These restrictions will inevitably increase prices for organically certified fish meal, and as such, certifiable replacement proteins must be investigated for the aquaculture industry to support the rapid growth
experienced in the organic agriculture sector.


Alternate protein sources

Most alternate protein sources are of plant origin and each has deficiencies when compared against fish meal.

Poorer digestibility, lower availability of some essential amino acids and palatability issues all contribute to limitations of plant protein replacement of fish meal (New, 2001). Additionally, many alternate plant protein sources contain anti-nutritional factors that can affect performance of aquafeeds. Naturally occurring compounds such as trypsin inhibitors, hemagglutinating agents, phytic acid, gossypol and glucosinolates are just a few of the more prominent anti-nutritional factors that must be considered in aquafeed formulations that utilize alternate protein sources if animal production is not to be compromised.

While many studies have investigated the use of plant protein sources in aquafeeds, the majority have utilized plant proteins that contain more than one anti-nutritional factor. This complicates data analysis in terms of identifying the specific cause of decreased growth often observed at higher inclusion levels (Francis et al., 2001). Comparatively few comprehensive studies have investigated the impact of anti-nutritional factors upon aquacultured species (El- Sayed et al., 2000; Bureau et al., 1998; Twibell and Brown, 2000 for review). If alternate proteins are to be utilized to their fullest potential, it will be imperative for such studies to become more numerous.

Soybean meal currently represents the predominant choice as an alternate protein source in aquafeeds. This is due to its relatively high protein content and suitable amino acid profile except for methionine. Soybean meals have been incorporated into many aquafeed formulations at a wide range of inclusion levels. In fact, formal evaluations of soybean meal in aquafeeds have been conducted on over 50 species of aquacultured animals (Brown and Smith, 2002; Forster, 2002).

However, as with most alternate protein sources, the use of soybean meal in replacing fish meal is not without problems. Many higher level carnivores are limited in the amount of soybean meal they can tolerate in feed formulations. For example, the marine carnivore cobia (Rachycenton canadum) can accept up to 40% replacement of fish meal with soybean meal without detrimental impact on growth performance (Chou et al., 2004). However, at elevated inclusion rates, weight gain decreases significantly. Other species, such as tilapia and catfish, can tolerate much greater inclusion levels of soybean meal and other plant protein sources, provided their amino acid requirements, usually for methionine and lysine, are met through other sources.

These species typically do not have the palatability problems with high levels of soybean meal that other, mainly carnivorous, species experience. Feeds for the marine Pacific white shrimp Litopenaeus vannamei have also been developed, relying upon soybean meal as a replacement protein source for fish meal (Mendoza et al., 2001; Davis and Arnold, 2000). This in itself is quite remarkable since traditionally shrimp feeds have relied heavily upon fish meals.

While soybean meal and its associated products have made great inroads into aquaculture nutrition, the industry cannot solely depend upon this source to provide the protein and oil needed to supply the projected demand for seafood and aquatic products. Indeed, the numbers are astounding. By 2030, the world’s population will exceed 10 billion. Maintenance of current levels of protein intake will require a 50% increase in fishery production.

At present, global landed seafood production approaches 130 mmt (FAO, 2002), with capture fisheries accounting for approximately 91 mmt of the total. Projected per capita seafood consumption will rise from 13.1 kg/year to over 21 kg/year by the year 2030. This equates to an increase in landings of seafood to levels approaching 190 mmt – a shortfall of approximately 60 mmt given the most recent estimates for capture fisheries production (FAO, 2002). It has been estimated that each year between 20 and 40 mmt of seafood are discarded at sea (Alverson et al., 1994; FAO, 1997).

Even assuming that total discard tonnage (by-catch) can be utilized for human consumption, there will nonetheless be a deficit of some 20-25 mmt of seafood.

Due to the low quality and usually smaller sized fish captured as by-catch, the deficit number will probably be closer to 40-50 mmt, as 100% utilization of current and future by-catch is highly unlikely (FAO, 1997).

The only feasible method of meeting seafood insufficiencies therefore, will be through enhanced production by aquaculture, which in turn will demand substantial protein sources to drive the industry.

Assuming a 1.5 food conversion ratio and an average fish meal inclusion rate as low as 10%, this represents a need for an additional 6-7.5 mmt of fish meal, a sum that, given current forecasts, simply cannot be met or sustained through captive fisheries. The situation with fish oil is even more daunting. New and Wijkstrom (2002) predict that global use of fish oil in the aquaculture industries will reach 145% of historical levels by the year 2015 and that if replacement oils or other supplies of fish oil do not increase, the impact of this usage by producers of shrimp and carnivorous fish will be felt well before 2010. A major limiting factor to the growth of the aquaculture industry will be the availability of economic and sustainable alternate protein and lipid sources that can maintain optimal production characteristics of cultured animals. These sources must be highly digestible, nutritionally efficient, of consistent high quality and availability, and finally, sustainable.

Expansion of the organic sector Recent trends in consumer buying habits illustrate a rapid expansion of the organic agriculture sector. In fact, the global value of organic food and drink markets is approximately US$25 billion, with the US dominating the market with US$11-13 billion in retail sales (International Trade Centre, 2002). These markets have been expanding at a rate of over 20% annually since the 1990s and are expected to experience similar growth for the next several years (Dimitri and Greene, 2002).

Organic production is appealing to producers for many reasons: as an alternative to the often destructive practices of conventional agriculture, producing a healthier product, as well as for the higher return that organic products can deliver (Mansfield, 2004). Current organic production cannot keep up with demand, which drives prices for organic products even higher, potentially discouraging budget-conscious consumers. However, with increasing production will come decreasing production costs and more stable, albeit higher, prices for the organically-inclined consumer.


THE IMPORTANCE OF DIETARY FORMULATIONS

Arguably, the most limiting and controversial aspect of organic production is the ability to formulate diets that are certifiable for organically produced animals. Since organic farming is based upon adjustments to production practices (Mansfield, 2004), these modifications are fairly easily attained. For example, organic livestock regulations stipulate that animals are maintained in living conditions that accommodate their normal behavior (205.239 of the National Organic Livestock Rules); that is, a specific space requirement per livestock animal is regulated. This usually can be easily satisfied and therefore presents no major problem to the organic producer. However, fulfilling dietary needs with certified organic rations is much more daunting, especially for higher level carnivores, with which traditional agriculture has no experience.

Another aspect of organic production involves the health and well-being of the cultured animal. Dietary needs and the sustained supply of required nutrients certainly affect the health and wellbeing of animals, especially those under culture conditions, even those organically certified. Finally, organic production must leave the environment in an improved condition relative to the position prior to initiation of production. Certainly, dietary formulations have the most dramatic impact upon the environment of the cultured animal. Therefore, dietary formulations cross over three of the five major areas that must be satisfied before a production facility can be certified as organic, and as such, deserve much attention if the demand for organic products is to be fulfilled.

Clearly, the most confusing aspect of the entire situation is the lack of uniform standards, most noticeably in the aquaculture industry. The American organic livestock business has a set of standards recognized by the National Organics Standard Board and the National Organic Program (NOP) of the United States Department of Agriculture. These standards must be followed and preserved for organic certification to remain in place. In these guidelines, dietary formulations or feeding regimes must be approved and certified.

The availability of organically certified animal or plant protein sources represents the major obstacle to the production of organically cultured fish, shellfish and other terrestrial meats. Many of these species require animal proteins, or have protein requirements that are difficult to satisfy using only traditional plant protein sources. Dietary needs must also be met to ensure that the animal is healthy under conditions of culture. If such needs cannot be met with certified organic protein sources, the animal is either incapable of being produced under organic guidelines, or the producer can petition to have a specific dietary item included in the organically certified ration - a process that could take up to two years (Richard Mathews, Associate Deputy Director USDA-AMS NOP, personal communication, 2004).


GMOS AND TRACEABILITY ISSUES

An extremely important area of concern with regard to organic standards is the current inability to utilize genetically modified organisms (GMO), including soybean and corn meals from GM plants. All protein sources from GMO are strictly prohibited in all drafts of organic standards worldwide. This further limits the available sources of high protein, highly digestible, costeffective feedstuffs that can be utilized in aquafeeds.

An additional challenge is the ability to track and certify feedstuffs for use in organic feeds. Traceability represents an important issue not only in the organic certification process, but also in food safety and biosecurity terms. Traceability will be increasingly important as organic standards are developed, revised, and ultimately, become more stringent. Therefore, research must be directed towards protein and oil supplies that are completely traceable and certifiable in terms of contemporary organic standards. While an increasing acreage of certifiable organic crops has developed, there is growing concern that these may become tainted by GM products, thereby compromising organic products as certifiable protein sources, which would result in a decline in consumer confidence. While paper trails and documentation may alleviate some of these issues, anxieties relating to GM contamination may result in more stringent certification procedures and recommendations in the future.


ORGANIC AQUACULTURE

Organic production is an area of intense interest for the aquaculture industry. Currently, there are no standards for organic production of aquatic species in the US, which contrasts to the situation in the EU and several Canadian provinces, which possess specific guidelines.

The USDA is rapidly trying to implement standards through several task forces within the USDA’s NOP.

These standards are, nevertheless, most likely 2-3 years away. However, interest in organic aquaculture in America is at an all time high and many producers are moving towards organic production utilizing not only EU and Canadian standards, but also by following the general guidelines for the organic production of terrestrial livestock, conventions which have been approved by the NOP. While this certainly represents a gamble to these producers, in terms of following rules not approved for their particular species, the lack of coherent and standardized guidelines for organic production of aquatic species has forced many aquaculture producers interested in this exploding sector of agriculture to take this risk.

Certainly, there are species that are ‘close’ to organic production, mainly from a dietary formulation standpoint. Herbivores and omnivores, such as tilapia and catfish, are much closer to organic production simply due to their dietary requirements and the feedstuffs that can adequately supply them. Shrimp also are close to organic production in terms of dietary formulations. Indeed, two shrimp producers in the US have been licensed by a third party certification company for organic shrimp production.

However, the USDA does not currently recognize these companies as being certified by the NOP and as such, they are not allowed to utilize the USDA seal of organic produce. Still, this activity does demonstrate that organic production of aquatic animals is moving towards a firm reality, and as such, attention should be paid as to how to aid this young and rapidly expanding sector of agricultural production.

Due to the overwhelming importance of dietary formulations in the organic certification process, alternate protein and lipid sources, especially for marine carnivores, must be thoroughly investigated and exploited whenever feasible. While increased constraints on fish meal and oil inclusion in organic aquaculture will clearly restrict the species that can be considered for production, current standards will allow for the organic culture of carnivorous species. For these species, research on fish meal and fish oil substitution meshes nicely with the current trends in aquaculture nutrition to reduce the dependence on capture fisheries.


ORGANIC AQUACULTURE RESEARCH

Research into organic formulations has been steadily increasing over the last several years. However, due to the fact that in the US, standards for organic production of finfish and crustaceans are under development and thus subject to change and revision, nutritional research has progressed slowly. As with general aquaculture nutrition, a priority area of research in organic aquaculture nutrition has been reduction and potential elimination of fish meal and fish oil in feeds.

Certified organic feedstuffs and other ingredients allowed under organic certification are published in the National List of Allowed Substances. However, every feedstuff and supplement that is already on the National List requires further investigation, since sustained residence on the List is renewable every five years. Organic standards could be modified and further strengthened in the future to protect the organic labeling process and procedures.

Therefore, presently listed compounds or feedstuffs are by no means secured for the future and deserve further research.


Yeast, its by-products and the viability of NuProTM as an organic protein source for aquafeeds

A number of studies have examined the efficacy of various yeast products as alternative or supplemental protein sources for inclusion into aquafeeds (Sanderson and Jolly, 1994; Hoffman et al., 1997; Olvera-Novoa
et al., 2002; Rodriguez et al., 2003; Li and Gatlin, 2004; Muzinic et al., 2004; Cheng et al., 2004). In general, these studies have returned promising results. However, to date, no research has examined the possibility of employing purely organically certified yeast products as protein supplements or as the sole source of protein in diets for young animals.

Research into the use of alternative protein sources at Virginia Tech has revolved around the inclusion and use of organically certifiable protein sources. These protein sources are currently scarce and often are either low in crude protein concentrations, which make them unsuitable for aquafeed formulations due to higher dietary protein requirement of many aquacultured organisms, or they are impractical due to high costs. Three trials were conducted with three different species: tilapia (Oreochromis niloticus), Pacific white shrimp and cobia.

In the US, these species represent the gamut of organic aquaculture potential, ranging from the species most likely to receive organic certification (tilapia), a crustacean that already has certified producers in the US (Pacific white shrimp) and a high level marine carnivore which presents major challenges for production and organic certification (cobia).


TILAPIA

Initial trials examined the possibility of replacing traditional protein sources (fish and soybean meals) in aquafeeds with an alternative, organically certified yeast protein (NuProTM). Diets were formulated using graded levels of NuProTM (0-100%), in place of soybean meal.

Tilapia (~15 g) were fed diets (n=10 fish/tank in triplicate) for 8 wks. Fish were fed 6% BW per day.

Fish were group-weighed weekly to adjust feed rations.

At trial termination fish were examined for percent weight gain, feed efficiency and biological indices (n=15/treatment). Muscle and liver lipid concentrations also were examined (n=9/treatment) to examine the potential impact of NuProTM upon production characteristics.

Irrespective of level of dietary incorporation, fish fed NuProTM-containing diets outperformed tilapia fed a commercial diet (Figure 1). Weight gain in tilapia fed diets containing NuProTM ranged from 319-458%, compared to 277% for fish fed the commercial feed.

However, the commercial feed returned better feed conversions. Graded replacement of soybean meal with NuProTM resulted in superior (P<0.05) performance at NuProTM levels of 20, 40 and 80%. When NuProTM served as the only protein source, no difference was observed in weight gain compared to animals fed control and commercial diets. Visceral index and muscle ratios were unaffected by diet. IPF ratios and hepatic lipid levels were all lower (P<0.05) when compared to fish fed commercial feed. Excepting the 80% diet, muscle lipid was lower in fish fed NuProTM-based diets compared with commercial feed.

This trial indicated that NuProTM could effectively replace 100% of the protein source in tilapia aquafeeds.

Figure 1.The impact of replacing the soybean meal component of tilapia diets with graded levels of NuProTM and total dietary protein replacement with NuProTM upon the growth performance of Nile tilapia. Asterisks indicate significant differences (P < 0.05) versus controls.

Moreover, and of increasing importance to the consumer, NuProTM represents a certified, fully traceable organic protein source. Furthermore, NuProTM significantly reduces muscle lipid levels in the edible component of the fish, which provides a leaner and potentially healthier product for the marketplace. A reduction in hepatic lipid levels may also be beneficial to the health status of cultured tilapia.


MARINE SHRIMP

A field trial was undertaken at a commercial facility (Permian Sea Shrimp Co. [PSSC], Imperial, TX) using six 4-acre grow-out ponds. Each pond was stocked in late May 2003 with 650,000 PL8 shrimp. Average water temperatures throughout the trial ranged between 24 and 28oC and pond salinity was 12 ppt. Ponds were randomly assigned to one of two dietary treatments.

Diet 1 was a commercial shrimp feed containing 12% fish meal that had been organically certified by a third party certification service. Diet 2 replaced 67% of dietary fish meal, reducing its concentration to 4% of the diet, using NuPro™. Diets were fed twice daily according to PSSC feeding schedules based upon weekly cast net sampling and shrimp were harvested 22 weeks later.

At harvest, animals fed either the NuProTMsupplemented diets or commercial shrimp feeds were compared based upon weight gain measured as percent increase from initial weight (Figure 2). Shrimp fed the commercial diet returned an average weight gain, from week 7 of the trial to harvest, of 387%. In contrast, animals fed the NuProTM supplemented feeds expressed an average weight gain of 526%. Average final individual weights of shrimp fed the NuProTMsupplemented diets was approximately 19 g vs 12 g for shrimp fed the organically certified shrimp feed.

The results from this study provided strong indications of production benefit in supplementation of shrimp diets with NuProTM. Importantly, this protein source provided the means to not only replace a non-traceable protein in shrimp diets but also permitted production of organic product. More in-depth studies are required to examine the impact of NuProTM upon production characteristics of shrimp held under differing husbandry conditions.

These two trials certainly indicate that NuProTM could serve as a basis for an aquafeed that could meet or exceed all present and future organic standards for certification.


COBIA

A six-week feeding trial was conducted to investigate the potential of NuProTM to replace fish meal in aquafeeds designed for a high level marine carnivore. Four experimental diets were formulated to provide 40% crude protein (CP) and 11% dietary lipid on a dry weight basis. These diets contained incrementally higher levels of NuProTM in replacement of fish meal (0, 25, 50 and 75% replacement). A fifth experimental diet was formulated to provide 40% CP solely from NuProTM.

Diets were fed to triplicate groups of 10 cobia (initial group weight 110 g). Fish were hand-fed twice daily, with total rations being divided into two equal feedings.

At the end of the trial, three fish from each group were weighed and dissected to provide biological indices (visceral somatic index, hepatosomatic index, muscle ratio).

Figure 2.The influence of NuProTM as an organic dietary protein source during the pond rearing of Pacific white shrimp. Animals fed NuProTM-based diets out-performed shrimp fed a certified organic feed formulation (P < 0.05).

After six weeks, weight gain ranged from 86 to 512% increase from initial weight (Figure 3). Cobia were able to accept a 25% inclusion rate of NuProTM for fish meal without significant detrimental impact on weight gain, feed efficiency, or other production characteristics.

Weight gain was not significantly compromised until reaching the 75% NuProTM inclusion rate, although a numeric decline occurred in cobia fed the 50% NuProTM inclusion rate. These data suggest that at a minimum, NuProTM can replace 25% of fish meal in diets for cobia, with more research needed to ascertain the upper level of inclusion without negative impact upon production characteristics. At high levels of NuProTM inclusion, there was an obvious palatability problem with this yeastbased diet, which is perhaps not too surprising given the carnivorous nature of cobia.

However, feed conversion ratios increased dramatically with increasing NuProTM inclusion (2.0 in fish fed 25% NuProTM vs 9.0 in fish fed 100% NuProTM), illustrating an additional problem in the use of alternate protein sources, especially for marine carnivores. The increased conversion ratios observed likely relate to palatability issues, which might override the beneficial aspects of this protein source for cobia. Nevertheless, a 25% reduction in the fish meal component for such a high level carnivore represents an impressive result indeed. It is highly likely that these animals will require several alternate protein sources in combination to replace fish meal in their aquafeed formulations.

Further research is planned to not only investigate NuProTM inclusion with other alternate protein sources in aquafeeds for cobia, but also to further investigate other potential benefits of utilizing NuProTM in aquafeeds. For example, at higher inclusion levels (such as 25%), NuProTM acts as an excellent binder. This must be investigated for the obvious benefit of having a binder with protein sparing qualities.

Additionally, in the tilapia trial, an increase in macrophage respiratory burst activity was observed in fish fed diets containing NuProTM (Figure 4). This most assuredly demands further attention, for if an immune function benefit is determined to be another aspect of NuProTM inclusion in aquafeeds, the potential of this organically certifiable alternate protein source is much greater still. The complete dietary impacts of NuProTM inclusion in aquafeeds certainly have not been fully investigated and clearly, results from these initial trials at the Virginia Tech Aquaculture Center need to be further developed to elucidate the mechanism(s) of action of this organically certified product.

Figure 3.The impact of graded replacement of fish meal with NuProTM upon the growth performance of cobia over a six week period. Significant differences (P < 0.05) in weight gain were detected when fish meal replacement exceeded 25%.

Figure 4. The effect of differing concentrations of NuPro™ upon respiratory burst activities of tilapia splenic macrophages.

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