The development of the embryo in the egg case can be divided into four stages. The temperature of the tank water directly affects the stages of embryo development.
The first stage occurs around two to 21 days. In this stage, the embryo is very active and measures 0.06 to 0.1 inches (1.5 to 2.5 mm). It is often hard to visualize in the first few days, as it is a very thin embryo.
The second stage occurs around 28 to 35 days. The embryo measures around 1.2 to 2.4 inches (30 to 60 mm) and is not as active in this stage. The end of the egg case develops an open split, which air can enter if the egg case is brought out of the tank.
The third stage occurs around 42 to 60 days. The embryos begin looking like adults in shape and markings. The ocelli, the classic black spot near the gills, is apparent. Embryos are 3.3 to 4.65 inches (85 to 118 mm) in length.
The fourth stage occurs around 70 to 90 days. These are “mini adults.”
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