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Using Soybean Meal And DDGS In Crayfish Diets

Interest in the production of Australian red claw has increased over the past few years and the species is commercially cultured in several countries including China, Mexico and Australia. Researchers from Kentucky State University, Aquaculture Research Centre look at the use of soybean meal and distiller's dried grains (DDGS) as feed for Australia Red Claw grown in ponds.

Introduction

Currently, there is little production of red claw in the United States. In Kentucky, red claw has attracted interest as a potential aquaculture species due to the success of growing them at Kentucky State University’s (KSU) Aquaculture Research Center during the past decade. In the early 2000s, KSU researchers produced the most red claw (by weight) in North America. Research at KSU has found the following favorable culture traits: they consume a prepared diet directly after hatching; grow rapidly up to (65-90 grams or 1/7 to 1/5 of a pound) in a limited (<120 days) growing season in temperate-climate ponds; and are highly-desired by consumers because of their lobster-like appearance, large size, excellent flavour, and good storage quality (Figures 1 and 2).

Notably, red claw grow larger than the most-commonly cultured crayfish in North America, the red swamp cray fish, which attains an average weight of between 20 to 35 g. Further, while the red swamp crayfish has a tail meat yield of between 15-20 per cent, red claw tail meat yield is approximately 30 per cent. Red claw have a straightforward production technology; tolerance of a wide range of water temperatures (15-32C) and low dissolved oxygen concentrations (as low as 1 part per million; no post-hatch larval phase, negating the need for expensive and sophisticated hatcheries; are tolerant of crowded conditions and non-burrowing behavior; and readily accept prepared diets, especially newly-released individuals which can reduce or eliminate the need to feed on live foods.

Although red claw seems to be a promising aquaculture species for US farmers, there are production challenges that need to be assessed before this enterprise can grow. Since red claw are a subtropical species, culture of red claw in temperate climate ponds is constrained by a short growing season. Further, red claw juveniles are not readily-available in the US; therefore, producers must purchase these individuals from hatcheries in other countries (Australia or Mexico) and costs can be higher than $1.00 (US) per juvenile (includes transport costs). There are red claw hatcheries in the US; however, they tend to be dedicated to the aquarium hobbyist, and prices are very high ($1.00-3.50 per juvenile) making them too expensive for purchase by producers who need many thousands to stock in their ponds.

Use of an inexpensive formulated diet is essential for profitability in the US Protein is generally the most expensive component in a prepared diet for fish or crustaceans. In addition, fish meal (FM) is generally the most desirable animal protein ingredient because of its high protein content and digestibility, excellent source of essential fatty acids and energy and its high palatability. Therefore, in an effort to reduce diet costs, it would be necessary to either reduce the protein level and/or replace FM with a less expensive protein source(s), such as soybean meal (SBM). The purpose of the present study was to determine growth, survival, total yield (lbs/acre) and processing characteristics of red claw fed diets with two different crude protein levels (18 per cent and 28 per cent), with or without FM present.

Materials and Methods

Juvenile red claw (5.75 g) were stocked into ponds (1/10th acre) and fed one of four diets: Diet 1 contained 18 per cent protein with FM; Diet 2 contained 18 per cent protein without FM; Diet 3 contained 28 per cent protein with FM; and Diet 4 contained 28 per cent protein without FM. The even number diets (Diets 2 and 4) contained SBM and distiller’s dried grain with solubles (DDGS) as replacements for FM (Table 1). Red claw were fed twice daily by distributing feed pellets over the entire surface area of each pond at 8:00 a.m. and 3:30 p.m. for 97 days. At harvest, ponds were completely drained and red claw were manually removed, hand-counted and individually weighed (Figure 3).

Results and Conclusions

After 97 days, the final mean weights of red claw fed Diet 3 (28 per cent protein with FM) and Diet 4 (28 per cent protein without FM) were significantly (P < 0.05) higher than those of red claw fed Diet 1 (18 per cent protein with FM) and Diet 2 (18 per cent protein without FM; Figure 4). Percent survival and total yield did not differ significantly among treatments, averaging 65.2 per cent and 652 lbs/acre, respectively. Processing traits of red claw revealed that males and females fed Diets 3 and 4 had numerically the highest tail muscle meat (no shell) weight and claw weight for females.

The results of the present study indicate that red claw grown in ponds can be fed a diet in which FM is completely replaced with a combination of plant-protein ingredients (SBM and DDGS) when the protein level is 28 per cent crude protein (CP).

However, when red claw were fed diets containing 18 per cent CP, growth and processing traits are reduced. The use of soybean meal (SBM), when combined with distiller’s dried grains with solubles (DDGS), offers much promise as a replacement for FM since diet costs can be reduced. Soybean meal is the most widely-used plant protein source in aquafeeds because of its high protein content, satisfactory essential amino acid composition, reasonable price, consistent quality, and steady supply.

DDGS contains moderately high protein content (28-32 per cent) and is the by-product from distillation of ethyl alcohol from grain or grain mixtures. The use of less-expensive, but nutritious, plant-protein ingredients, such as SBM and DDGS, is critical to reducing aquaculture diet costs so that the US can be competitive in the global marketplace. Further research needs to be conducted on the use of SBM and other alternative protein sources to reduce diet costs for red claw, thereby increasing the sustainability and profitability for producers in the future.

May 2011

the Fish Site Editor

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