Abstract

A simple and effective method was used for testing water stable diets suitable for crayfish feeding. The first experiment evaluated the effects of adding increasing amounts of water (D1: 26; D2: 31; D3: 35 and D4: 39% by weight) to dietary pellets during mixing and before drying. The hardness of the pellets and nutrient losses after the pellets had been immersed in water for 1, 2, 4 and 8 h were studied. The diet contained 36.8% crude protein (CP) and 8.5% ether extract (EE) on a dry matter (d.m.) basis, and 3% sodium alginate. In the second experiment, the same diet with different binders and 39% water was evaluated for hardness and nutrient leaching. The binders used were: A: 3% sodium alginate; B: 2% agar; C: 2% carboxy methyl cellulose (CMC); D: 1% sodium alginate + 1% CMC; E: 1% sodium alginate + 1% agar; F: 1.5% sodium alginate + 1.5% agar; and G: 1.5% sodium alginate + 1.5% CMC. Leaching of nutrients was measured by randomly immersing triplicate 5 g pellet samples, contained in nylon bags (porosity: 40 ?m), for 1, 2, 4 or 8 h in 12 L aquaria (temperature: 28.5 ± 0.43 °C). In the first experiment, the lowest dry matter loss was after 1 and 2 h of water exposure in D4 (mean: 1.58% and 6.84%, respectively), and dry matter losses increased to a mean of 13.72 after 4 and 8 h, with no differences between diets. Shear strengths were the same in D3 and D4, and were significantly higher than those measured in D1 and D2. In the second experiment, after 8 h of water immersion, diet G had the least losses (13.67%), followed by diets A and F. The greatest loss was with diet C (24.18%). Shear strength was significantly higher in diet A, followed by diets E, G and D, and similar values were measured in diets B, C and F. Dietary protein and lipid contents increased and mineral and carbohydrate contents decreased after immersion of the pellets in water for 8 h.

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