Obligate, continuous, non-selective filter feeders such as Artemia have disadvantages compared to other zooplankton because they can not select their food. When considering food for these animals, two factors have to be taken into account: first, the particle size and stability in water, and second, the nutritional quality. In this experiment nutritional quality of the food was evaluated in terms of digestibility, which is a major component of its nutritional value since ingested food has to be digested before the nutrients become available for the animal. Previous experiments have shown that fresh baker's yeast Saccharomyces cerevisiae can be considered as food for Artemia because of its particle size, stability and nutritional content. However, utilizing fresh baker's yeast is ineffective because of its low digestibility. Therefore the cell wall was chemically treated to make it digestible for the brine shrimp. The efficiency of this process was evaluated in terms of feeding kinetics and growth tests. Feeding tests show that Artemia ingest treated yeast at a higher rate, compared to untreated yeast. This was confirmed for various strains of baker's yeast (FBY, B1 and R5). This was also true when Artemia was fed on yeast, harvested at different phases. However, the feeding rate was higher on the yeast harvested at exponential phase than yeast harvested at stationary phase. The maximum feeding rate for untreated and treated fresh baker's yeast was obtained at concentrations ranging from 200 to 300 10³ cells/ml and equalled 316 10³ and 537 10² cells/animal h-1, respectively. Gut passage time experiments showed that day 4 individuals did not fill their gut when they were being fed on untreated yeast at concentrations ranging from 100 10³ to 2000 10³ cells/ml. Artemia fed on treated yeast showed a gut passage time between 20 and 40 min at a yeast concentration ranging from 2000 to 1000 cells/ml. To test the nutritional quality of the yeast, short-term growth tests were done with different strains of yeast (FBY, B1 and R1) as well as the yeast harvested in different growth phases. Artemia , fed on treated yeast, had considerable higher growth and survival rates than those grown on untreated yeast. Twenty-four hour acclimation experiments were done to test if the kind of food and the concentration will affect feeding rates during the tests. Results show that Artemia , acclimated on algae or algae in combination with dried food had significantly higher feeding rates than those acclimatized on the food at which feeding rate was conducted. Water renewal, prior to the feeding tests, did not affect the feeding rate. |
