Artemia: A Model Specimen

Figure 3 : Examples of camera-microscope setups. (a) Digital SLR camera fi tted with a suitable lens adapted to a trinocular photo-tube with a photo eyepiece 10×. (b) Digital bridge camera with an integrated zoom lens mounted with a vario (zoom) photo ocular 5× to 12.5×. (c) Special microscope camera mounted with a photo eyepiece 10×. (d) Compact digital camera mounted with a monocular tube. (e) Smartphone-adapter (UNIKOP, manufactured by Immunocons Co., Germany) mounted with a stereo microscope. This adapter consists of a variable holder so that smartphones of different sizes can be used.

T e natural color of individuals is infl uenced by the quality of water. When the salt concentration is low, the utilization of oxygen is most eff ective. Over the course of several days some water may evaporate and the concentration of salt will increase in the remaining volume of water. At that point the utilization of oxygen is reduced so that the production of hemoglobin is intensifi ed and the colorization of Artemia is shiſt ed to red. T us, red colorization is an indicator of hypoxemia. In this case an adequate proportion of fresh water should be added. T ese color shiſt s from gray to bronze to reddish can be seen in the image sequences of Figure 4 .

Young larvae showed only a stereotypical movement similar to breast-stroke swimming ( Figure 5a ). At the beginning of the third phase of development (days 4–6), additional asynchrony patterns could be seen comparable with swimming the crawl ( Figure 5b ). In the course of phase 4, some larvae could be observed swimming as a couple showing synchronized formations of movement ( Figure 6 ). Some days later, even looping, forward rolls, and other complex movement patterns could be observed ( Figure 7 ). Aſt er a period of four weeks, only a few individuals survived, and on the 35th day of observation the last animal expired.


Digital image processing . Photomicrographs taken from Artemia were also used for introduc- tions to digital image processing. In particular, bright-fi eld images were digitally inverted by use of standard imaging soſt ware so that digital “dark-fi eld” images could be obtained revealing fi ne details with an improved clarity. T e appearance and fascinating appeal of such inverted images was similar to X-ray images ( Figure 8 ). T e appearance of an inverted bright- fi eld image was strongly infl uenced by the exposure and the range of contrast between specimen and background. When photomicrographs were taken in brightfi eld and properly exposed, the background was whitish, and high-density specimens appeared rather dark, leading to a high range of contrast ( Figure 8 ). In underexposed bright-fi eld images the range of contrast was reduced signifi cantly: the background showed a lower brightness and a yellowish or orange tint. T us, the background was no longer black or dark when a digital inversion was carried out. In such images fi ne nuances of density could be revealed such that the appearance of the inverted image ( Figure 9 ) seemed to be similar to (negative) phase contrast. In comparison to real darkfi eld, digital “dark-fi eld” images did not

show the specimens in their natural color, but they were free from typical artifacts oſt en seen in normal dark-fi eld images, such as ultra-bright contours (marginal irradiation) and other eff ects of refl ection caused by a very bright illuminating light, such as blooming and scattering. Similarly, digital “phase- contrast” images were free from typical artifacts associated with true phase-contrast imaging such as haloing and shade-off (further explanations in web source [d]). Suggestions of further experiments . Observations of growth and locomotion can be made with naked eyes even by very young children so that children´s inherent interest in nature can be stimulated when Artemia is presented in classrooms and integrated into lessons (web source [e]). T rough successive microscopic observations of Artemia, young students can be introduced to several principles of scientifi c work. For instance, larvae can be photographed daily, and their body length measured. Since there is a well-defi ned number of individuals, the body length can be averaged for each day of observation, and corresponding standard deviations can be calculated. Based on these data, kinetics of growth can be graphically demonstrated and mathematically described ( Figure 10 ). • 2018 July

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