Artemia nauplii and two commercial replacements as dietary supplement for juvenile signal crayfish, Pacifastacus leniusculus (Astacidae), from the onset of exogenous feeding under controlled conditions

Two 100-day experiments were carried out under controlled conditions to evaluate effects of different dietary supplements on survival and growth of juvenile Pacifastacus leniusculus from the onset of exogenous feeding (stage 2). In the first experiment, a dry diet for salmonids was supplemented with six levels of freshly hatched Artemia nauplii, starting at 50, 100, 300, 500, 1000 nauplii per crayfish per day increased by 15% every 20 days, and nauplii in excess. Survival did not show significant differences, ranging from 75 to 90%. Crayfish receiving nauplii in excess had significantly higher carapace length (16.63 mm) and weight (1238.43 mg) than the other treatment groups. No significant differences were observed among the treatment groups starting at 300, 500 and 1000 nauplii per crayfish per day, averaging 15.18 mm carapace length and 975.60 mg weight. Considering costs and these results, an initial amount of 300–500 nauplii per crayfish per day increased by 15% every 20 days could be a reasonable option during the first 100 days of rearing. In a second experiment, partial substitution (50%) of nauplii with two commercial Artemia replacements was tried as supplement to the dry diet alone. Treatments were 500 nauplii per crayfish per day, 250 nauplii + 250 Artemac and 250 nauplii + 250 Proton, increased by 15% every 20 days. During the trial (at days 20, 40, 60 and 80) no significant differences were found, either in survival or in growth. At the end of the experiment, similar survival (approximately 80%) and growth (approximately 14.50 mm and 850 mg) were obtained with both Artemia replacements and with Artemia only. Results showed that these replacements can be used from the onset of exogenous feeding.