Transition to Artemia feeding phase for orchid dottyback Pseudochromis fridmani larvae: establishing suitable prey shift time and strategy

Marine finfish hatcheries often replace small live prey with the larger traditional prey, brine shrimp Artemia, to feed the growing fish larvae. However, research on fish larviculture, including marine ornamental fish, often overlooks the importance of fine-tuning such prey transition. This study investigated the suitable time and approach for the larvae of an ornamental species, orchid dottyback Pseudochromis fridmani, to transit to the Artemia feeding phase. In experiment I, the suitable prey shift time window was estimated by abruptly feeding P. fridmani larvae with newly hatched Artemia nauplii (AN) from 5, 8, 11 or 14 days post-hatching (DPH) until 19 DPH. Although P. fridmani could ingest AN from 5 DPH, the final larval survival of 11-DPH and 14-DPH treatments were significantly higher, and it might relate to the enhanced digestive capability of older larvae. In experiment II, when prey shift began on 9, 11, or 13 DPH, the larvae were either abruptly shifted (AS) to AN feeding, or given a three-day gradual transition (GT) period of co-feeding original prey (rotifers and copepods) with AN before completing the prey switch. By 22 DPH, the prey shift strategy of GT significantly improved larval survival compared to the AS treatments; prey shift time treatments of 11-DPH and 13-DPH also reached significantly higher survival than 9-DPH treatments. However, survival of all individual treatments continued to decrease in the final stage of experiment. To further improve the prey transition success, experiment III investigated the effects of Artemia enrichment and prey shift time, by abruptly feeding larvae with either AN or enriched Artemia metanauplii (EA) from 9, 11, or 13 DPH onwards. Although the larvae fed AN were significantly larger than those fed EA, the absolute differences were small. There was a significant interaction between Artemia type and prey shift time on larval survival. The EA-11-DPH and EA-13-DPH treatments maintained steady survival post prey transition, and reached the highest mean survival of 58 ± 10%, and 55 ± 12% by 20 DPH, respectively. Moreover, while the larvae fed AN abnormally reduced prey intake over time, most larvae in EA-11-DPH and EA-13-DPH treatments still maintained high Artemia ingestion. These results suggest that dietary highly unsaturated fatty acids in enriched Artemia were crucial for larval survival of P. fridmani. Overall, this study shows that P. fridmani larvae could skip AN and directly feed on EA from 11 DPH without compromising survival or feeding performance