Evaluation of four dietary protein sources for use in microbound diets fed to megalopae of the blue swimmer crab, Portunus pelagicus

Abstract

Introduction of formulated diet particles for larval culture will simplify hatchery protocols and promote consistent survival, while decreasing total operating costs. The blue swimmer crab, Portunus pelagicus, is a commercially important species with substantial aquaculture potentials in the Indo-Pacific region. Feeding trials aimed at investigating protein nutrition of P. pelagicus larvae were undertaken with the megalopae instar. Microbound diets (MBD) with four different dietary protein sources (fish meal, squid meal, krill meal and soybean meal) were formulated and fed to newly molted megalopae until they metamorphosed to the first crab stage. Thirty megalopae were reared individually for each dietary treatment, with the addition of two control treatments of megalopae fed live Artemia nauplii and an unfed treatment. Survival was high for all fed treatments (73.3–93.3%), while total mortality was recorded for the unfed control. Megalopae fed the fish meal based MBD demonstrated higher survival than that of megalopea fed live Artemia, suggesting that MBD have the potential to completely replace live food for the culture of P. pelagicus megalopae without adversely affecting their survival. These results also suggest that P. pelagicus megalopae are able to adapt to a range of dietary protein sources. For megalopae fed live Artemia nauplii, mean development time was significantly shorter (4.0 ± 0.4 days) and the mean carapace width and dry weight of newly settled first stage crabs were significantly greater, (3.1 ± 0.0 mm, 1.3 ± 0.1 mg, respectively) than megalopae in all other fed treatments. Among MBD treatments, no significant difference in mean development time was detected, however, the mean carapace width of crabs that metamorphosed from megalopae fed fish meal based MBD (2.8 ± 0.0 mm) was larger than those fed squid meal based MBD (2.6 ±0.0 mm) and the mean dry weight of individuals fed fish meal based MBD (0.87 ± 0.04 mg) was also significantly heavier than those fed soybean meal based MBD (0.72 ± 0.04 mg). The outcome of this research provides valuable information regarding protein requirements of P. pelagicus megalopae and will aid in optimising formulated diet particles for potential use in commercial hatcheries.