Additional supply of decapsulated Artemia

The additional supply of live feeds such as Artemia remains indispensable in juvenile astacid rearing from the start of independent life. Considering that cost and work could be reduced by restricting this supply, a 100-day experiment was carried out with stage 2 Pacifastacus leniusculus to evaluate the effects of different administration periods of decapsulted Artemia cysts as supplement to a dry diet at two stocking densities. Using a bifactorial design, six treatments differing in the time at which the cysts were withdrawn (after 20, 30 or 50 days of experiment) and the stocking density (100 or 200 crayfish·m-2) were conducted. Survival rates did not show significant differences among groups, with final figures averaging 81%. Crayfish receiving cysts up to day 50 showed faster growth (around 13.8 mm carapace length and 610 mg weight at the end of the experiment) than the rest, significant differences being recorded from day 60 of experiment onwards. The 20-day and 30-day supplies resulted in similar growth values. There were no significant differences in survival or growth between 100 and 200 crayfish·m-2. This study shows that decapsulated Artemia cysts can be withdrawn at day 20 (allowing to feed a dry diet as the sole food thereafter) and that faster growth can be obtained if cysts are supplied up to day 50. Furthermore, a stocking density of 200 crayfish·m-2 can be advised under the mentioned feeding conditions

Proposal of a practical diet for juvenile astacid crayfish studies from the onset of exogenous feeding under controlled conditions

Considering the knowledge on freshwater crayfish feeding requirements and other cultured crustaceans, a practical extruded diet was formulated with the aim to be used for juvenile astacid studies from the onset of exogenous feeding. According to a bifactorial design, the practical diet was compared with the diet which has allowed repeated good survival and growth results (control: feedstuff for trout combined with Artemia cysts) in groups and individually isolated crayfish in an 80-day experiment. Diets tested did not affect final survival rates and growth neither in grouped nor in isolated crayfish, being the highest survival rate (average: 93%) and growth values (average: 13.2 mm carapace length: CL, 578.1 mg weight: W, 3.52%·d-1 specific growth rate: SGR, 1896.6% weight gain: WG) reached with the practical diet. Survival rates did not show significant differences neither among crayfish maintained in groups (86% for the practical diet and 81.7% for the control diet) nor among isolated crayfish (100% survival). Isolated crayfish had significantly higher growth (14.3 mm CL, 760 mg W) than the grouped crayfish (11.5 mm CL, 354 mg W). Results show the feasibility of the proposed practical diet as basis for further studies on astacid crayfish

Antifungal treatments in artificial incubation of crayfish eggs (

Considering the concerns about the safety of the use of formaldehyde as antifungal agent, the effects of three alternative chemicals (potassium sorbate, copper hydroxide and magnesium chloride) were tested in the artificial incubation of signal crayfish (Pacifastacus leniusculus) eggs. Eight treatments were performed during 15 min every other day: formaldehyde at 3000 ppm (control), potassium sorbate at 5000 and 10000 ppm, copper hydroxide at 40, 60, 80 and 200 ppm, and magnesium chloride at 10000 ppm. Eggs were incubated in a flow through system at a density of 20 eggs·cm−2. After 61 days of incubation, the highest efficiencies were obtained with 200 ppm of copper hydroxide (77.6% of survivors to stage 2) with no significant differences from the control (74.3%). Lower concentrations of copper hydroxide resulted in high egg mortality whereas potassium sorbate and magnesium chloride were ineffective to avoid fungal growth and total egg mortality took place. From the obtained results, copper hydroxide baths at 200 ppm could be considered as a good alternative to formaldehyde

Antifungal treatments in artificial incubation of crayfish eggs (Pacifastacus leniusculus, Astacidae): Searching for alternatives to formaldehyde

Considering the concerns about the safety of the use of formaldehyde as antifungal agent, the effects of three alternative chemicals (potassium sorbate, copper hydroxide and magnesium chloride) were tested in the artificial incubation of signal crayfish (Pacifastacus leniusculus) eggs. Eight treatments were performed during 15 min every other day: formaldehyde at 3000 ppm (control), potassium sorbate at 5000 and 10000 ppm, copper hydroxide at 40, 60, 80 and 200 ppm, and magnesium chloride at 10000 ppm. Eggs were incubated in a flow through system at a density of 20 eggs·cm−2. After 61 days of incubation, the highest efficiencies were obtained with 200 ppm of copper hydroxide (77.6% of survivors to stage 2) with no significant differences from the control (74.3%). Lower concentrations of copper hydroxide resulted in high egg mortality whereas potassium sorbate and magnesium chloride were ineffective to avoid fungal growth and total egg mortality took place. From the obtained results, copper hydroxide baths at 200 ppm could be considered as a good alternative to formaldehyde

The effects of various binders and moisture content on pellet stability of research diets for freshwater crayfish

Two experiments were conducted to assess the water stability of a practical research diet manufactured with various binders and differing levels of moisture. In the first experiment the binders &ndash; agar, gelatine, carrageenan, and carboxymethylcellulose (CMC) were included at both 3 and 5% of total ingredient weight. All binders were tested with equal ingredient weight to water volume, and additionally carrageenan was tested in a diet with double the water volume. The dry matter remaining following immersion for up to 180 min was calculated and the rate of pellet decay was modelled using the Weibull distribution. The analysis revealed that the rate of dry matter loss decreased with time, and that carrageenan and CMC binders were significantly better (P &lt; 0.001) binders than the agar and gelatine. The 5% binder concentration slowed the decay rate by as much as 62% as compared with the 3% binder concentration. The second experiment compared the binding performance of carrageenan and sodium alginate in both 50% moisture and 10% moisture pellets. The same analysis revealed that 10% moisture alginate-bound pellets were more water stable than the others. A discussion of the use of moist diets for crayfish research is included.<br /