Acclimatization of Chlorella to Seawater

Abstract

Despite success in raising farm animals with chlorella as a basic diet, previous attempts at using this freshwater organism as nutritive source for marine plankton and larvae of shell fish had difficulities in that the chlorella was not always digested well by larval shellfish, and that the propagation in seawater of high salinity (S 34‰) was unfeasibly poor.
The present research was designed to explore a possibility of using the chlorella as food for larva of tunas and other fish. The material was prepared by culturing Chlorella ellipsoidea in freshwater which was fed with a diluted liquid fertilizer from time to time. The initial density of the organism in the suspension was 8×10⁶/ml in number of cells. In determining the effect of chlorinity on the propagation the chlorella suspension in experiment A was admixed with seawater (Cl 19‰) at the ratio of 1:1; in experiment B one part of seawater (Cl 19‰) received one half of chlorella suspension twice in two days; in experiment C the culturing water consisting of one chlorella suspension and a quarter of seawater (Cl 19‰) was renewed with a quarter of seawater six times at intervals of two days. While the cultured organism in A and B needed about 40 days to attain a maximum concentration (30×l0⁶/ml), experiment C was effective in producing the concentration of 37×l0⁶/ml in 11 days. Chlorinity at the end of those experiments was respectively 12.50, 16.44, and 21.12‰. During experiment C over a month the average diameter of the cells was reduced from 9.3 to 2.0μ with some of the smallest individuals occurring as early as 10 days after onset of the experiment.
In subsequent experiments an increase in the number of cells from the initial level was 15×l0⁶/ml in 15 days for two mean temperatures 16° and 21°C but it was 25×l0⁶/ml in 18 days at 26°C. Among various ratios of inoculation, 1/4, 1/8, 1/16, of chlorella suspension to the culturing seawater, the second one had the best result, increasing the number of cells by 25×l0⁶ml in 20 days. In the presence of a commercial fertilizer, however, the quarter inoculation revealed better effect with an increase of the number of cells being 60×l0⁶/ml in 16 days.
On a future occasion detailed accounts of breeding copepods and other zooplankton (50-70μ in diameter) with the chlorella adapted to seawater will be made in connection with its digestibility.