Weaning of hatchery-reared greenback flounder ( Rhombosolea tapirina Günther) from live to artificial diets: Effects of age and duration of the changeover period

The greenback flounder ( Rhombosolea tapirina) is a potential culture species in Australia, but poor survival has been recorded during weaning from live Artemia to artificial diets. This paper describes the results of three experiments on the effects of fish age and the duration of the changeover period from live to artificial food on weaning survival and subsequent growth. Fish weaned for 10 days from Day 50 post-hatch or later had higher mortality ( P < 0.05) than fish weaned earlier, but no differences in final weights or lengths ( P > 0.05) were observed between fish weaned on different days post-hatch. Weaning from Artemia 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 between Artemia and artificial diets resulted in a reduction in final length ( P < 0.05) compared with overlaps of 10 or 20 days, but no difference in survival ( P > 0.05). Overlaps of 20 days resulted in significantly 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 to result in the best growth and highest survival rate, but a 10-day overlap may result in reduced Artemia cost with minimal effect on performance.