RNA:DNA ratio for diagnosis of the nutritional condition of Japanese anchovy Engraulis japonicus larvae during the first-feeding 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.