The effects of live prey and greenwater on the early larval rearing of orchid dottyback Pseudochromis fridmani

Abstract

Captive breeding of marine ornamental fish is considered as a sustainable alternative to the current practice of fishing the wild stocks to supply the marine aquarium trade. However, efficient larviculture remains the biggest bottleneck, as many marine ornamentals suffered total mortality or only have extremely low survival at early larval stage. This study investigated the optimal conditions for the rearing of early larvae of a valuable ornamental fish, the orchid dottyback Pseudochromis fridmani, in terms of density and combination of live prey, as well as the application of the “greenwater” technique. In the first experiment, larvae were reared in clearwater and fed rotifers at 2, 5, 15, and 40 mL−1. Although there was no significant difference in larval survival among treatments on 8 days post-hatching (DPH), the larvae fed higher rotifer densities (15 and 40 rotifers mL−1) had significantly better growth. In the second experiment, by 8 DPH, a significant interaction between rearing condition (clearwater vs. greenwater) and live prey combination (rotifers only vs co-feed rotifers and copepods) on larval survival was detected, and the mean survival of larvae co-fed rotifers and copepods in clearwater (18%) was significantly lower than the other treatments (45–64%). Moreover, larvae reared in greenwater, or co-fed rotifers and copepods, grew significantly larger than those reared in clearwater, or fed rotifers only, respectively. In the third experiment, the larval survival was higher cell density of Nannochloropsis paste (NAN) used to make greenwater (0–3.40 × 106 NAN cells mL−1). The larval survival of the highest algae density treatment was the highest on 8 DPH (72 ± 8%), and it was significantly higher than those reared in the treatments of 1.13 × 106 or 0 NAN cells mL−1, but not significantly different from that of 2.27 × 106 cells mL−1 treatment. Overall, the results of this study suggest that co-feeding early P. fridmani larvae with rotifers and copepods, with the complementary use of greenwater comprising of ≥ 2.27 × 106 NAN cells mL−1, can enhance larval survival, growth and development. However, when the algal cell density is below this threshold, using such a co-feeding strategy may compromise the survival of P. fridmani larvae. The results of this study highlighted the importance of optimizing the application of live prey and greenwater for improving the survival of marine fish larvae.