MASS CULTURE OF FRESHWATER DIATOMS

Being rich in nutrition,freshwater diatoms are favored food of many aquaticanimals.In 1973,experiments were started to investigate the possibilities of culturingdiatoms as a source of food for the larvae of crabs,shellfish and other aquatic ani-mals.Through screening and cultivation for about a year,we have sorted out 4species of freshwater diatoms suitable for mass culture from the environs of Wuhan,namely,Nitzschia fonticola,N.palea,Hantzschia amphioxys,and Cyclotella meneghi-niana.N.fonticola has been chosen for a series of cultivation experiments.The lipidand protein contents,as well as 15 amino acids,are determined quantitatively.Wehave also prepared two new culture media,“HB-D 1”and“HB-D 2”,which provesatisfactory for the propagation of diatoms.The optimum temperature for the growth of N.fonticola is 20—30℃,optimumlight intensity,2,000—5,000 lux.We have observed the regularity of the absorptionand consumption of nitrogen,phosphorus and silicon by N.fonticola in both themiddle-scale experiment and the mass culture.Under our culturing conditions,itseems that silicon is the principal limiting factor.In the middle-scale experiments,whenthe nutritional elements were supplied in time throughout a period of 15 days,the cellcount increased up to 23×106/ml,O.D.420nm=40,corresponding to a yield of2.76 grams dry weight per litre.In the 30-litre mass culture experiment,harvestedone-sixth the total amount of the culture every 2 days,a yield corresponding to 7grams dry weight each time has been obtained consecutively.The culture removedwas replaced by fresh medium.Judging from our experimental results,we presumethat a steady high yield could be obtained should the culture be harvested every2.5 days at the rate of 1/6 each time.