Publication Date


Advisor(s) - Committee Chair

Rudolph Prins, Gary Dillard, Ernest Beal, Larry Gleason

Degree Program

Department of Biology

Degree Type

Master of Science


Ninety-day experiments were initiated in January (Expt. 1), June (Expt. 2), and October (Expt. 3) 1972, to characterize molting patterns of Orconectes immunis (Hagen) at three different temperatures (20 C, 24 C, and 28 C) and three different photoperiods (6 L, 15 L, and continuous light). For each experiment 144 animals were collected from the seasonally predominate size class of that period. Light intensity was regulated to 15 foot candles + 10. Experimental conditions were arranged in a 3 x 3 design for statistical analysis using a completely randomized design with factorial arrangement of treatments.

In all cases molting frequency was directly related to temperature (0.01 level of significance). Photoperiod did not significantly affect molting, nor were sexual differences in molting and these parameters apparent. Finally, no interactions between any of the parameters were found.

In animals collected in January, successful molting frequency was linear from 20 C (387 of the animals molted) to 28 C (27% of the animals molted). Mortalities were low (2%) and 117 of the animals did not attempt to molt.

In animals collected in June, 467 of the animals died in the molt process. Of these, 11% were malformed and 35% attempted to molt unsuccessfully. Unsuccessful molting was linear from 28 C (3 animals attempted to molt) to 20 C (38 animals attempted to molt). At 28 C there were 22 successful molts and at 20 C,6 successful molts.

In animals collected in October, the lowest number of successful molts, 11, occurred at 28 C and the highest number, 35, at 24 C. Linear and quadratic regressions were significant, indicating a relationship of successful molting frequency to temperature up to a certain point. Fifty-five percent of the animals did not attempt to molt and there was an overall mortality of 2%.

It was suggested that temperature apparently was the major factor involved in the molting of O. immunis in the experimental conditions of this study.


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