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Counting Eggs and Larvae Techniques used to count eggs include the "DISPLACEMENT METHOD", "IMAGE ANALYSIS", and "DIRECT COUNTING". |
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"DISPLACEMENT METHOD"
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This method is often used in the field as it is fast, yields immediate results, and is reasonably accurate. In this method a sub sample of several hundred eggs are counted and their volume measured (usually in a measuring cylinder). The volume of the total egg mass (including the sub sample) is then measured and the total number of eggs calculated. Inaccuracies with this method can occur through differences in the gel and egg size between different parts of the spawn mass. This is particularly the case in some experimental situations where spawn masses may be of low quality with variable gel and egg quality. SN = sub sample number. TN = TV/SV x SN |
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"IMAGE ANALYSIS" In this method a image is made of the spread out egg mass placed against a contrasting background. The number of eggs can then be counted and marked of the image by hand, or an image analysis program can be used. Inaccuracies with this method can occur through overlapping eggs making counting difficult. This is particularly the case where the eggs are in a globular mass rather than in strings. To some extent this method can also be used for larvae if they are in shallow trays. It may be convenient to separate the eggs using cysteine to dissolve the gel. |
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ImageJ program allows for easy counting of eggs. It automatically counts all objects it recognizes (in red below). ImageJ 1.33u: Wayne Rasband, National Institutes of Health, USA; http://rsb.info.nih.gov/ij/ |
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This method produces an accurate count of eggs or larvae. However, it can only be used when the eggs are dissociated (see de-gel eggs), or when the larvae have separated from the gel naturally or naturally. The end of a disposable plastic pipette is cut to leave the maximum open tube. Eggs or larvae (up to just below the diameter of the tube) can then be aspirated and counted and placed in a new container. This method is often used to count and separate larvae from eggs. |
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A complete disposable pipette (below) and one with the
end removed (above) with toad eggs (middle left) and larvae (middle right).
Plastic disposable pipettes are graduated in diameter at the ends. The
pipette is generally best cut of to give the maximum diameter.
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A disposable pipette with the end removed and aspirated
eggs. The 15 eggs can easily be counted as they are transferred into a
new container. Similarly larvae or small swim ups can also be counted
by this method.
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A petri dish with a batch of mainly un-hatched eggs and a few toad larvae. To prevent hypoxic and unsanitary water the larvae must be moved to a new container with fresh water. This is easily done using a disposable plastic pipette. |
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