BURYING AND MOLTING OF PINK SHRIMP, PENAEUS-DUORARUM (CRUSTACEA-PENAEIDAE), UNDER SELECTED PHOTOPERIODS OF WHITE-LIGHT AND UV-LIGHT

Five groups of shrimp of similar size were subjected to different photoperiods of white and UV light for 56 days. Data were collected semidiurnally on their burying and molting behavior, summarized into four 2 wk periods, and analyzed statistically. The shrimp''s activity above the substrate was inversely related to the amount of exposure to light. Most activity was exhibited by shrimp exposed to no light. A circadian burying rhythm was manifest in shrimp held in continuous white light, but not in shrimp held in continuous UV-light. Shrimp irradiated with continuous UV-light exhibited significantly more activity during the periods coinciding with the new and 1st-quarter moon than during the full and last-quarter moon. Light was the predominent factor governing the shrimp''s burying behavior. No statistically significant differences were found for the overall molt rates among the various lighting conditions. Molt rate was constant in all groups after the first 2 wk, but growth rate declined significantly during the last 4 wk. Ecdysis occurred during the scotophase in groups with a light and dark cycle. Those kept in the absence of light molted significantly more during the time period corresponding with the scotophase of other groups indicating the presence of an endogenous molt rhythm. Overall, shrimp molted an average of once every 14 days.