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Artemia: A Model Specimen


Figure 4 : Morphological differentiation of Artemia franciscana , from day 1 through day 35. The labeling of the single images indicates the age of the individual animals in days. Dark-fi eld imaging with a low magnifi cation lens (Pl 2.5/0.08), a zoom-ocular 5×–12.5×, and fl ash illumination (according to the arrangement shown in Figure 3b ). The width of fi eld changes as the organism grows. See Figure 10 for typical organism lengths through day 14. Colorization is modulated from bright gray to yellowish to reddish as the concentration of salt increases in the water.


In other experiments several environmental parameters could be modified, such as the concentration of salt, pH-value, water temperature, materials for feeding, or the population density. Correlations of such parameters with growth kinetics and/or the maximal duration of survival could be undertaken. The results derived from such experi- ments could be compared with published data compiled in the literature. Figure 10 (modified from [ 6 ]) and Figure 11 (modified from [ 7 ]) give examples of published findings with regard to different feeding protocols and varying population densities. These experiments reveal that feeding soybean waste and corn bran is more efficient than a rice bran diet and that the growth rate is significantly reduced when the population density increases. In other experiments the influence of environmental parameters on the hatching rate of Artemia cysts can be evaluated (example reported in web source [f]). Thus, Artemia could be used for introductory pedagogic projects focused on repetitive measurements, statistical presentations and analyses, and environmental and ecological research experimentation.


Discussion


Young people (children and school students) of today are the scientists of tomorrow. T eir interest in exploring nature should be stimulated as early and successfully as possible. In this respect, Artemia can be regarded as an attractive “model organism” of high pedagogical value. T ese aquatic “household pets” can be purchased at low cost, and they can be cultivated without diffi culty. Moreover, these organisms tolerate wide ranges of temperature, pH-values, and salt concentrations. On the other hand, one must feed Artemia carefully so that


2018 July • www.microscopy-today.com


over-eating is avoided and the quality of water can be maintained. When the water appears somewhat cloudy or foul, about one-third of the volume should be replaced by a new portion of fresh salt water.


Since individual sizes range from 0.5 to 15 mm over the course of development, these animals can be observed from day one, even with naked eyes. On the other hand, various magnifying equipment can be used by young (and advanced) explorers, from simple loupes and student microscopes to stereo microscopes and high-end laboratory microscopes. Examinations can be carried out with low or medium magnifying lenses that operate at long working distances from the specimen and can be handled well by young users. While brightfi eld is always available and is the most widely used illumination mode, standard dark-fi eld mode is especially recommended as a tool for impressive microscopy. In the latter technique, Artemia appears in natural colors, as long


Figure 5 : Synchronic movement patterns (a) similar to breast-stroke swimming (day 4), (b) asynchrony movement patterns comparable with swimming the crawl (day 6). Dark-fi eld, objective Pl 2.5/0.08, fl ash.


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