16 March 2009 Effects of feeding practical diets containing different protein levels to Australian red claw (Cherax quadricarinatus) Linda S. Metts, Kenneth R. Thompson, Laura A. Muzinic and Carl D. Webster1 Interest in the production of Australian red claw (Cherax quadricarinatus) has increased over the past few years and the species is commercially cultured in several countries including China, Mexico and Australia. Currently, production of red claw in the US is small and it is unclear if commercial production of red claw will develop into an industry in the future. The advantages of raising red claw include the following: they consume a prepared diet right after hatching, grow rapidly up to (65-90 g) in a limited growing season (<120 days) in temperate climate ponds and are highly-desired by consumers because of their lobster-like appearance, large size, excellent flavor and good storage quality. However, raising red claw in the US can be rather costly as a result of a lack of large commercial, domestic hatcheries. There are red claw hatcheries in the US but thy tend to be dedicated to the hobbyist, where red claw are highlyprized in the aquarium industry. Red claw purchased from these suppliers tend to be very expensive ($1-3/individual not including transportation costs), which precludes their purchase by pond producers who need many thousands to stock. Pond producers of red claw, thus, must purchase them from hatcheries in other countries (Australia or Mexico) and costs can range from US$0.50-0.55 per juvenile including transportation costs. Feed costs can represent up to 70 percent of the total operating expenses of an aquaculture enterprise. Thus, recent efforts to determine specific nutrient requirements and evaluate inexpensive practical diets have been devoted to reducing diet costs and, possibly, increasing profits. Development of a cost-effective and nutritionally-balanced formulated diet is essential, especially for US red claw producers. Protein is generally the most expensive component in a prepared feed for fish or crustaceans. In addition, fishmeal 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 costs, it would be necessary to either reduce the protein level and/or replace fishmeal with a less expensive protein source. While information about specific nutritional requirements and practical diet formulations for red claw is increasing, there is no information on the partial or total replacement of fishmeal with other dietary protein levels for red claw grown in ponds. The purpose of the present study was to determine growth, survival, body proximate composition and processing characteristics of red claw fed diets with two different protein levels with or without fishmeal. Experimental Design Juvenile red claw (5.75±3.3 g) were obtained from a commercial supplier2 and stocked into twelve, 0.04-ha ponds at a rate of 1,000 per pond. Groups of 100 live red claw were hand-counted at random until all ponds had been stocked. Three replicate ponds were assigned to one of four practical diets that were formulated to contain two levels of protein (18 percent and 28 percent), with or without menhaden fishmeal (Table 1). Dietary ingredients were processed into 5 mm sinking pellets by a commercial feed mill3. Red claw were fed twice daily by distributing pellets over the entire surface area of each pond between 0800 and 0830, and between 1530 and 1600 for 97 days. All red claw were fed the same amount of diet based on age and estimated body weight using a feeding schedule devised by C.D. Webster4 with survival assumed to be 65 percent. The target harvest weight was 80 g. The amount of diet fed was adjusted every 2 weeks. At the end of the experiment, ponds were completely drained and red claw were manually removed. Red claw were hand-counted, individually weighed and sexed. Twenty males and twenty females from each pond were randomly sampled and chill-killed in an ice bath. Red claw were kept frozen (-15ºC) until analysis. Measurements of claw weight, tail weight, tail muscle weight, and cephalothorax weight were made. Results At the conclusion of the feeding trial, the final mean weights of red claw fed Diet 3 (28 percent protein with fishmeal) and Diet 4 (28 percent protein without fishmeal) were significantly higher (58.5 g and 62.4 g) than those of red claw fed Diet 1 (18 percent protein with fishmeal; 51.7 g) and Diet 2 (18 percent protein without fishmeal; 53.0 g). Likewise, red claw fed Diets 3 and 4 had significantly higher weight gain (894 percent and 959 percent) compared to red claw fed Diet 1 (778 percent) and Diet 2 (799 percent) as shown in Figure 1. Specific growth rate (SGR) of red claw
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