Females are dissected
in order to determine whether or not they are mature. During
dissection several eggs are removed from the tip of one of
the ovaries and the developmental stage of these eggs
indicates maturity. A circular incision (A) is made behind
the eye socket on one side of the carapace and eggs are then
removed from the incision. The eggs are staged on a scale of
1-6 (see below) where stage 1 is immature (C) and stages 4
and higher are mature (D). The incision is then patched up
with super glue and duct tape and the lobster is placed in a
recovery tank.
Ovarian Egg Stage In the Laboratory
After the eggs are removed they are placed under a dissecting microscope next to a ruler in order to measure the range of sizes of the eggs and to describe their color. They are assigned an egg stage according to the criteria listed below the pictures. Stages 1-3 are immature, and stages 4 and higher are mature.
Stage 1: White <0.5 mm Stage 2: Yellow, beige, pale green <0.8 mm Stage 3: Light to medium green <1.0 mm Stage 4: Medium to dark green 0.1-1.6 mm Stage 5: Dark green 1.0-1.6 mm Stage 6: Dark green 1.4-1.6 mm Stage 6A: Oocytes free Spent: White or yellow with dark green residual ova
* Criteria are defined by
Aiken, D.E. and Waddy, S.L. 1982. Cement Gland Development, Ovary
Maturation, and Reproductive Cycles in the American Lobster Homarus
americanus. Journal of Crustacean Biology 2(3): 315-327.
Berried females that are captured by participating fishermen are measured and the developmental stage of the eggs that they are carrying is recorded. Egg stages range from 1-4 and are determined by color as well as the presence or absence of an eye spot. The following pictures illustrate the four stages recorded. Below this field key are more detailed pictures of eggs at each stage taken under a microscope.
For our purposes, we record four egg stages instead of five, as it is difficult to distinguish between stages 2-4 in the field. Our distinctions are as follows: Stage 1: All black, Stage 2: Some eggs have a lighter half, Stage 3: Eggs have an eye spot, Stage 4: Eggs are brown.
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*Helluy, S. and Beltz, B.S. 1991. Embryonic development of an American lobster (Homaurs americanus): Quantitative staging and characterization of an embryonic molt cycle. Biol. Bull..180: 355-371.
Following dissection a pleopod is removed from the female
for viewing under a dissecting microscope. Female lobsters
develop cement glands in their pleopods prior to egg
extrusion. It is believed that these glands become engorged
with a sticky material that "cements" the eggs to the
lobster's abdomen once they are extruded. These cement glands are visible under the microscope and
the stage of their development can be determined. They are
milky white and fill in from the edges of the pleopod
towards the center. The stages are determined by the percent
of the surface covered by the glands. Stage 1: <25% Stage 2: 25-50% Stage 3: 50-75% Stage 4: 75-100%.
* Criteria are
defined by Aiken, D.E. and Waddy, S.L. 1982. Cement Gland
Development, Ovary Maturation, and Reproductive Cycles in the
American Lobster Homarus americanus. Journal of Crustacean Biology
2(3): 315-327.
As female lobsters approach maturity the width of their
adomen increases relative to their carapace length so that
they will be better able to carry their eggs. The picture to
directly to the right illustrates a widened abdomen relative
to the narrow abdomen to the far right. The increase of this
ratio (abdomen width/carapace length) in females relative to
the constant ratio observed in males is an indication of the
onset of maturity. See graph below.
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A small amount of fluid is removed from the spermatheca
of the female to check for the presence of a spermatophore.
This sample is examined under a compound microscope (10x).
Lobster sperm are non-motile and are therefore tail-less.
However, they do have three antennae at the head end.
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