Eggshell as a sustainable calcium source for improving molting performance in freshwater Red Claw Crayfish, Cherax quadricarinatus culture

This study evaluated the effects of natural calcium carbonate sources, eggshell (ES) and seashell (SS) powders on growth performance, survival, molting frequency, and exoskeletal calcium accumulation in juvenile red claw crayfish (Cherax quadricarinatus). Juveniles (0.21 ± 0.01 g) were reared for 60 days under five treatments (0, 5, 10, 15 mg ES L⁻1 and 15 mg SS L⁻1) in a static-water culture system equipped with biofiltration. All groups were fed a formulated diet containing 30% crude protein, 8% crude lipid, and 6% eggshell powder. No significant differences (P > 0.05) were observed in growth performance (2.55–2.65% day⁻1), FCR (1.55–1.69), or survival (71–78%) among treatments. Nevertheless, there is a trend of improved growth performance with the addition of calcium in water. In addition, molting frequency and carapace calcium content were significantly higher (P < 0.05) at 15 mg L⁻1 for both ES and SS treatments compared with other treatments. Both calcium concentration in culture water (R = 0.89) and carapace calcium (R = 0.82) exhibited strong positive correlations with molting frequency. While supplementing calcium through the water appeared to have minimal effects on growth and survival once dietary calcium requirements were met, it exerted clear positive effects on molting performance. Considering their abundance and low cost, eggshells therefore represent a practical, affordable, and sustainable calcium source for enhancing molting success in freshwater crayfish culture systems.