Abstract:

This experiment was conducted in 250 ml beakers and 300 L plastic pools to find out the instars duration (duration between two moults), total duration and instars number (larval moult) during the larval cycle of Macrobrachium gangeticum. The instars duration from stages I-V was 8-14 days (10.4 ± 2.88 days) recorded in 250 ml beakers which was comparatively longer than that of the plastic pools at 5-7 days (5.75± 0.957 days). Similar trend with a slight increase of 12-16 days (14.2 ±1.788 days) in instars duration in beaker was observed between stages V-VI and found much shorter duration of 5-6 days (5.25±0.5 days) in plastic pools. Further, a comparatively longer instars duration of 19-27 days (22.6 ±1.788 days) was observed between stages VI-XI in beaker than in plastic pools of 8-10 days (9.0±1.154 days). Same trend existed at later stages XI-PL, which was slightly longer in both treatments i.e. 9-10 days (9.6 ± 0.547 days), in beakers and 2-3 days (2.5±0.577 days) in plastic pools. The total instars duration of 49-62 days (57.4± 4.929 days) from stage I-PL was recorded in 250 ml beakers which was comparatively much longer than that of 300 l plastic pools of 20-25 days (22.5 ± 2.380 days).

The instars number (number of moults) varied significantly during the larval cy-cle of M. gangeticum carried out in 250 ml beakers. Zoea I passed through 11 distinct larval stages to attain post larval stage. A minimum of 4 moults from stages I-V, and a maximum of 5-7 moults (5.8±1.095) between stages V-VI, thereafter 5-9 moults (7.4±2.28) from stages VI-XI and 4-5 moults (4.25±0.44) between stages XI-PL were recorded in this species.

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Date 2010/02/15

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