TEMPERATURE-CONTROLLED MERISTIC VARIATION IN THE PARADISE FISH MACROPODUS OPERCULARS (L.)

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Abstract
Eggs from one pair of paradise fish Macropodus opercularis (L.) were reared at different constant temperatures, and the effects were noted on dorsal and anal fin ray, spine and basal counts, caudal and pectoral ray counts, and vertebral counts. Some young were transferred from low to high temperatures after varying periods to determine the duration of sensitivity of meristic series to environmental influence. Intermediate sustained temperature produced significantly fewer vertebrae than either low or high temperature. Different rearing temperatures produced different ray, spine, and basal counts; variation in each of these series was largely independent of vertebral variation and of variation in the other series. Eggs hatched less than two days after fertilization, but some meristic series were still subject to environmental influence 20 days later. The order of fixation of the final count in different series roughly followed the order of their ontogenetic appearance. While "shock effect" was apparent in some changes produced by temperature transfers, there was a general tendency for counts of certain lots of fish transferred from low to high temperature to approximate counts of fish reared at sustained intermediate temperatures.

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