Tidal periodicity of molting in giant mud crab, Scylla serrata (forskål, 1775)

Abstract

Molting is the most crucial phase in the life cycle of mangrove crabs, leading to mortality in various culture systems. As a result of this exigency, this study was conducted to offer a cue in molting using the tidal cycle as one of the visible events in a natural context. Monitoring was carried out at every 1-hour interval (24 hours) day and night for 57 days to check for molting while taking into account key environmental elements such as tidal cycles, water current speed, and flow rate. The results showed that 70.6% of molting happened during high tide, with 93.8% of it occurring at night and 6.3% during the day. By contrast, only 29.4% occurred during low tide, showing a significant difference (T-test = 0.011, p < 0.05) between mean molts. Hence, the highest molting rate (88.2%) was observed between tidal episodes between the neap and middle cycles, with the middle tide (55.9%) occurring at 12.4±0.9 m/s, neap tide (32.4%) occurring at 16.8±2.0 m/s, and spring tide (11.8%) occurring at 9.5±1.2 m/s. Molting occurs at high tide because crabs' rheotactic behavioral responses to incoming new water help the crab's body fill with air and water throughout the molting process. Mangrove crabs employ their tidal periodicity of molting as a defense strategy against potential predators and mortality, and it can be used as a molting indicator in many culture systems.

Efficacy of different wet feeds on the growth performance of mud crab Scylla serrata during fattening in cages

“…The present study recorded the highest percentage of molting during night time. This is in accordance with the studies conducted byMirera and Mtile (2009) andBiag et al (2022).…”

“…Mirera and Mtile (2009) found 100% of molting in neap tide and high tide with gastropod as feed to mud crabs, whereas in current study neap tide had 90% molting and high tide had 100% molting, as opposed toBiag et al (2022) who obtained 70.6% molting during high tide and only 32.4% molting during spring tide. The present study recorded the highest percentage of molting during night time.…”