STUDIES ON THE DIGESTION OF ALGAE BY FISH (Ⅰ) THE DIGESTION AND ABSORPTION OF SCENEDESMUS OBLIQUUS BY SILVER CARP

In order to find out whether unicellular green algae could be digested by silver carp (Hypophthalmichthys molitrix), tracer experiments of 32P were carried out. Scenedesmus obliquus (Turp) Kutz was cultivated in HB No. 4 medium containing 32P of different specific activities (20 μCi/L, 30 μGi/L, 50 μCi/L) instead of 31P. After being cultivated for 72 hours, the algae were collected and their radio-activity was measured. The result showed that 32P was absorbed and accumulated rapidly by Scenedesmus obliquus. The rates of absorption were all over 98%.The fish were fed with thoroughly-washed labeled algae. After feeding 48 hours, the fish were taken out of the water, dissected, and various tissue samples were prepared.The results showed that Scenedesmus obliquus could be ingested, digested and absorbed by silver carp. The rates of ingestion ranged from 47% to 63%. Different tissues have different capacity for assimilating and accumulating 32P. According to the data at 48th hours (50μCi/L), the specific radioactivity of 32P accumulation were 4580 (intestine), 650 (liver), 609 (skeleton), 118 (muscle), 110 (brain) CPM/500mg. It is evident that Scenedesmus obliquus is not only ingested, but also digested and absorbed by silver carp. There is reason to think that unicellular green algae might play a more important role in the nutrition of silver carp than people used to believe.