Replacement of fish meal in cobia diets using an organically certified protein

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CHAPTER 2 Replacement of fish meal in cobia diets using a yeast-based organically certified protein

Abstract

A six-week feeding trial was conducted to evaluate the use of a yeast-based, certified organic protein source as a replacement for fish meal in diets for cobia (Rachycentron canadum). Five experimental diets were formulated to provide 40% crude protein and 11% dietary lipid (dry matter basis), with the yeast-based protein source replacing Special Select® menhaden fish meal at 25, 50, 75 and 100% of dietary protein. Ten juvenile cobia (initial weight, 11.5 g/fish) were randomly stocked in triplicate 300 l circular fiberglass tanks (n=30 treatment-1) and hand-fed the diets based upon total tank biomass twice daily at 0900 and 1400 h. Fish were group weighed weekly to monitor performance and adjust feeding rations. Water temperature and salinity were maintained at 27 C and 15 ‰, respectively. At the end of the feeding trial, weight gain, ranging from 86 to 512% , and feed efficiency ratio values, ranging from 0.17 to 0.53, were significantly affected by the inclusion of the yeast-based protein source, with decreasing values as inclusion levels of the yeast-based protein source rose above 50% of dietary protein. Cobia fed the diet containing 25% of dietary protein from the yeast-based protein source had equal weight gain and feed conversion ratio values as fish fed the control diet composed of 100% fish meal (503 vs 512 and 1.9 vs 1.9, respectively). Biological indices including hepatosomatic index, visceral somatic index and muscle ratio, were all similarly affected by inclusion of the yeast-based protein source, with significant impacts when inclusion levels rose above 50% of dietary protein. As with the weight gain and feed efficiency ratio values, fish fed the diet containing 25% of protein from the yeast-based source had values similar to those observed in the control animals. This study represents the first attempt to utilize an organically certified protein source as a replacement for fish meal in diets for juvenile cobia. Although levels of inclusion of the yeast-based protein source above 50% of dietary protein resulted in detrimental effects on production characteristics, the data clearly suggest that, at a minimum, 25% of dietary protein can be provided by this yeastbased protein in diets for cobia.
Key words: yeast, recirculating aquaculture, quality, composition, growth, cobia, Rachycentron canadum
Published: Lunger, A.N., Craig, S.R., McLean, E., 2006. Replacement of fish meal in cobia (Rachycentron canadum) diets using an organically certified protein. Aquaculture 257, 393-399.

 Introduction

Fish meal is generally considered to represent the “gold standard” dietary protein source for carnivorous fishes. However, even though the animal feedstuffs and competing industries have increased demands for fish meal, global production of this commodity has remained relatively stable over the last decade, and supplies are unlikely to increase (FAO, 2004). Indeed, the increasing scarcity of suitable protein sources for human consumption may result in the use of industrial fish for the plate, resulting in a further weakening in supplies (Craig and McLean, 2005). Already, aquafeeds account for > 50% of variable operating costs of intensive aquaculture operations, with protein representing the most costly feed ingredient (Bassompierre et al., 1997). If aquaculture is to continue to expand to meet global demands for seafood products, development of cost-effective and sustainable dietary formulations will be mandatory (Catacutan and Pagador, 2004). This only can occur through significant reductions in the dependence of the aquafeed industry upon fish meal supplies.
Because fish meal represents a finite resource and as it has become more expensive over time (FAO, 2004), it is not surprising to find that the aquafeed industry has sought out alternative, less expensive, protein sources. For alternative or supplemental proteins to be useful, however, they must possess certain characteristics. Alternative proteins must be competitively priced relative to fish meal on a unit protein basis. They cannot negatively impact fish performance (digestibility, growth, disease resistance, etc.) or product quality and must be commodities (i.e., traded internationally) (Hardy and Tacon, 2002). As well, alternative proteins must not be environmentally degrading with respect to nitrogen and phosphorus discharge and should be easily handled, stored and amenable to pelleting. Because of these restrictions, there presently exists, only a limited number of potential candidates. These include the pulses, oilseeds, grains, rendered animal meals, processing discards and fishery by-catch. Soybean meal, in particular, represents one of the most widely-used alternate protein sources employed by aquaculture, due to its global distribution, cost, relatively high digestibility, good amino acid profile and high protein content (Storebackken et al., 2000). Nevertheless, soybean and other alternative protein meals each contain a variety of anti nutritional factors that negatively impact production performance of cultured fish (Francis et al., 2001).
An issue of more recent concern relates to that of biosecurity and food safety. Western consumers have, due to enhanced education and increased access to scientific and media services, become more sophisticated in their purchasing decisions. In an age of bioterrorist threat, outbreak of unusual zöonoses (e.g., transmissible bovine spongiform encephalitis, severe acute respiratory syndrome), increasing health concerns related to chemical contaminants (Hites et al., 2004) and the advent of genetically modified organisms, more attention than ever before is being given to food quality and safety (Reid et al., 2004). This shift in consumer eating patterns has stimulated production of organic foods. As of the early 1980s, aquaculture represented the world’s fastest-growing food production sector. However, since 1999, for many countries organic agriculture has supplanted aquaculture as the fastest-growing food production sector (FAO, 1999; El-Hage Scialabba and Hattam, 2002). This trend continues on a global basis and includes a growing organic aquaculture segment. Interest in organic aquaculture is based primarily upon the potential profitability of the organic sector (Craig and McLean, 2005).
Although no official statistics are available with respect to organic aquaculture production, estimates suggest that in 2000 it did not exceed 5000 tons, which represents 0.01% of global aquaculture output (Bergleiter, 2001). This negligible production of certified aquaproduce underscores the difficulties inherent in achieving organic aquaculture standards. The principal problem encountered relates to sourcing organic feed and nutrient resources (Tacon and Pruder, 2001). Based on current estimates of certified organic aquaculture production and anticipated growth of the industry, it has been predicted that organic aquaculture harvests will achieve 1.2 million tons by 2030 (El-Hage Scialabba and Hattam, 2002). If such an increase is to be realized, however, new sources of certifiable feeds must be found. The search for organically certified alternate proteins, especially for carnivorous species, represents a greater challenge than securing alternative proteins alone. The present study was initiated with this challenge in mind.
The carnivorous cobia was used as an experimental animal due to the hardy nature of this fish and the increasing interest associated with this species. It is also believed that if fish meal can be completely eliminated from a high level marine carnivore diet, then it should be possible to remove all fish meal from diets for all other species as well. The organically certified yeastbased protein was employed as the alternative protein source in this study due to its relatively high crude protein levels and satisfactory amino acid profile.

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Materials and Methods

System and husbandry

The feeding trial was conducted at the Virginia Tech Aquaculture Center in Blacksburg, Virginia in a custom-designed, recirculating aquaculture system (RAS; Fig. 2.1). The RAS was comprised of twenty-four 300 l circular fiberglass tanks, a bubble-bead filter (BBF-2, Aquaculture Technologies Inc., Metaire, LA, USA) to remove suspended solids, a UV light sterilizer (Emperor Aquatics, Pottstown, PA, USA), a KMT fluidized bed with media (Kaldnes Inc., Providence, RI, USA) for biological filtration, and a side-looped protein skimmer (R&B Aquatic Distribution, Waring, TX, USA) to remove smaller solids and decrease turbidity. A thermostatically-controlled heater, placed in the biofilter sump, was employed to maintain water temperature at 27 degrees C. Water salinity was maintained at 15 ‰ with the addition of synthetic sea salts (Marine Enterprises International, Baltimore, MD, USA). Fish were exposed to a 12:12 light:dark cycle through fluorescent lighting positioned 8 m above the culture system. Water quality parameters during the feeding trial were as follows: dissolved oxygen, 6.10 + 0.24 mg/L; total ammonia nitrogen, 0.40 + 0.07mg/L; nitrite, 0.32 + 0.06 mg/L, nitrate, 8.78 + 3.33 mg/L; and pH, 7.57 + 0.19.
Juvenile cobias (Rachycentron canadum) were purchased from the Aquaculture Center of the Florida Keys and acclimated in four 1000 l tanks for 2 weeks. After the acclimation period, ten juvenile cobia, (average initial weight, 11.5 g/fish), were placed into each of 15 experimental tanks. Fish were hand-fed twice per day, at 09.00 and 16.00 h. The ration was divided equally between the two feedings, based upon total body weight, initially starting at 8% body weight per day, and decreased to 7% during the final week of the feeding trial which maintained a level of apparent satiation without overfeeding. Fish in tanks were group weighed weekly to adjust the feeding rates and monitor growth performance.

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 Diets

Menhaden fish meal (Special Select®, Omega Protein, Hammond, LA, USA) and a yeast-based product were the two protein sources utilized in this study. NuPro® is a certified organic yeast-based protein source comprising a mixture of nucleotides, peptides, and the contents of the cytoplasm. NuPro® was obtained from Alltech, Inc. (Nicholasville, KY, USA) and served as a replacement for fish meal in the experimental diets. The five experimental diets were isonitrogenous and consisted of a control diet (100% fish meal) and four other diets in which NuPro® replaced a proportion of fish meal (25, 50, 75, and 100% of dietary protein). The diets were formulated to provide 40% crude protein and 11% lipid on a dry weight basis, supplying 1243 kJ available energy /100 g dry diet, except for Diet 5 (0 fish meal/100% NuPro®) which was formulated to provide 1142 kJ available energy/100 g dry diet to meet the constraint of maintaining the diets as isonitrogenous (Table 2.1). Menhaden fish oil was used as the lipid source (Omega Oils, Reedville, VA USA) and dextrin was included in the diets as the carbohydrate source. Calcium phosphate was added to Diets 4 (25/75) and 5 (0/100) which contained higher inclusion levels of NuPro®, to balance dietary phosphorous levels.

Analyses

At the end of the feeding trial, three fish from each tank (N=9 treatment-1) were euthanized by an overdose of clove oil (Sigma-Aldrich, St. Louis, MO, USA) and bled via caudal venipuncture for measurement of packed cell volume (PCV) and plasma protein levels.
Fish were measured for length and weight and weight gain, feed efficiency ratio values (FE = g gain / g of weight gained), survival, visceral somatic index (VSI = visceral mass weight *100 / total body weight), hepatosomatic index (HSI = liver weight *100 / total body weight), and muscle ratio (MR = fillet weight *100 / total body weight) were calculated. Muscle and liver samples also were collected for proximate analysis, including crude protein, total lipid, dry matter and ash (AOAC, 1994). Liver samples were analyzed only for lipid due to sample size.
 

Statistical analyses

All data were subjected to analysis of variance utilizing SAS 9.1 (SAS, Cary, NC, USA). Where appropriate, data also were subjected to Duncan’s multiple range test for means separation. Differences were considered significant at α < 0.05.

Results

Weight gain ranged from 86 to 512% (Table 2.2) and was significantly affected by inclusion of the yeast-based protein source. There was a noted decrease (P < 0.0001) in weight gain with increasing inclusion of the yeast-based protein source, except for Diet 1 and Diet 2 which had similar weight gains of approximately 500%. Feed efficiency ratio values (FE) ranged from 0.17 (Diet 5) to 0.53 (Diets 1 and 2) with the FE decreasing (P < 0.0001) as inclusion rate of the yeast-based protein source increased (Table 2.2). Once again, there was no difference in growth between Diet 1 and Diet 2, and these two diets produced the highest feed efficiency ratio values during the feeding trial. Survival also was affected significantly by dietary treatment as the fish fed Diet 5 had lower survival (63%) compared to an overall survival rate of 99% among cobia fed the remaining diets (Table 2.2). Muscle protein also tended to decrease as inclusion of the yeast-based protein source increased, with a range of 17.8-19.7% (wet weight basis : Table 2.3).

Abstract
Acknowledgements
Chapter 1 General Introduction
Fish Meal
Soybean Meal
Corn Gluten Meal
Single-cell proteins
Miscellaneous Protein Sources
Carnivores vs. Omnivores/Herbivores
Antinutritional Factors
Organic Certification
Background on Cobia
Feeding Habits of Cobia in the Wild
Larval Cobia Requirements
Juvenile Cobia Requirements
Broodstock Nutrition
Summary
Literature Cited
Chapter 2 Replacement of fish meal in cobia diets using an organically certified protein
Abstract
Introduction
Materials and Methods
Results
Discussion
Literature Cited
Chapter 3 The effects of organic protein supplementation upon growth, feed conversion and quality parameters of juvenile cobia
Abstract
Introduction
Materials and Methods
Results
Discussion
Literature Cited
Chapter 4 Taurine addition to alternative dietary proteins used in fish meal replacement enhances growth of juvenile cobia
Abstract
Introduction
Materials and Methods
Results
Discussion
Literature Cited
Chapter 5 Summary Conclusions
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