WEANING OF HATCHERY-REARED GREENBACK FLOUNDER (RHOMBOSOLEA-TAPIRINA GUNTHER) FROM LIVE TO ARTIFICIAL DIETS - EFFECTS OF AGE AND DURATION OFTHE CHANGEOVER PERIOD

The greenback flounder (Rhombosolea tapirina) is a potential culture s pecies in Australia, but poor survival has been recorded during weanin g from live Artemia to artificial diets. This paper describes the resu lts of three experiments on the effects of fish age and the duration o f the changeover period from live to artificial food on weaning surviv al and subsequent growth. Fish weaned for 10 days from Day 50 post-hat ch or later had higher mortality (P < 0.05) than fish weaned earlier, but no differences in final weights or lengths (P > 0.05) were observe d between fish weaned on different days post-hatch. Weaning from Artem ia to artificial diets was shown to be possible from Day 23 post-hatch , with 82.2% survival after a 10-day overlap. An overlap of 5 days bet ween Artemia and artificial diets resulted in a reduction in final len gth (P < 0.05) compared with overlaps of 10 or 20 days, but no differe nce in survival (P > 0.05). Overlaps of 20 days resulted in significan tly heavier final weights (P < 0.05) than either 10 or 5 days. Weaning from Day 23 post-hatch with a 20-day overlap would therefore appear t o result in the best growth and highest survival rate, but a 10-day ov erlap may result in reduced Artemia cost with minimal effect on perfor mance.