Effects of rotifer, Brachionus rotundiformis in enhancing some digestive enzyme activities into glucose on somatic growth, RNA/DNA contents and some digestive enzyme activities of olive flounder Paralichthys olivaceus larvae

Abstract

We investigated the effects of enzyme enhanced rotifer (EER), Brachionus rotundiformis on growth, RNA/DNA contents and digestive enzyme activities in olive flounder Paralichthys olivaceus larvae. Digestive enzyme activities of rotifer were enhanced by putting glucose in culture medium, and then rotifers (NR, rotifer not supplied the glucose during culture, and EER) was supplied to 10 rotifers/ml in larval rearing tank twice daily. The length-daily growth rate (DGR) showed a sudden decrease at 7 days post hatch (dph), and the weight DGR showed two times decreasing at 5 and 8 dph. The larvae in the NR treatment underwent two times the decrease of daily growth rate of body weight, while those in the EER treatment underwent only the first decrease of that. The DNA content for both treatment increased constantly. The RNA content increased in the larvae measuring up to 3.7 mm in the NR treatment. However, the RNA content of the EER treatment increased in the larvae until the end of the experiment. Therefore, supplement of rotifer enhanced the digestive enzyme activities for early olive flounder larvae prevented the decrease of RNA contents related with a protein synthesis and body weight growth after 7 dph, because NR is not enough for early larvae. Key words: Enzyme enhanced activity, nucleic acid content, somatic growth, critical period, flounder larvae, Paralichthys olivaceus, rotifer.