RNA:DNA ratio for diagnosis of the nutritional condition of Japanese anchovy Engraulis japonicus larvae during the firstfeeding stage

Abstract

In order to establish criteria with which to evaluate the nutritional condition of wild first-feeding larvae of Japanese anchovy Engraulis japonicus, the whole body RNA:DNA ratio and daily protein growth rate of reared larvae were individually determined. Anchovy larvae were reared for up to 9 days after the first-feeding day at 20°C and 25°C under various feeding conditions. Percent survival of the group starved for 2 days after the first-feeding day was extremely lower than that of those fed from the first-feeding day and 1 day starved groups at the two temperatures, even if they were supplied with food thereafter. Therefore it was concluded that the point of no return (PNR) was between 1 and 2 days after the first-feeding day within this temperature range. The RNA:DNA ratio of the PNR criterion was determined. Also, a 0% growth formula was established representing the relationship between the daily growth rate in protein, RNA:DNA ratio and temperature for first-feeding larvae.