Effects of Different Seaweed Shelters on Survival and Molting of Scylla paramamosain during Megalopa-to-First-Crablet Transition

Abstract

The megalopa-to-first-crablet transition constitutes a critical developmental stage in the hatchery rearing of mud crab, Scylla paramamosain, during which newly metamorphosed crablets are particularly susceptible to cannibalism and physical injury. This study evaluated the effects of different seaweed species and shelter densities on the survival and molting rates of S. paramamosain during this developmental transition. The 4-day-old megalopae were reared for three days in seven treatments consisting of a control without shelter and three seaweed species, Caulerpa lentillifera, Gracilaria fisheri, and Kappaphycus alvarezii, each provided at 1 and 2 kg/m². The experiment was conducted using a completely randomized design with three replicates per treatment. Survival and molting rates were determined at the end of the rearing period. It was found that seaweed shelter significantly affected both survival and molting rates. The highest survival (83.3 ± 15.0%) and molting rate (81.9 ± 16.8%) were observed in crablets provided with G. fisheri at 2 kg/m², whereas the control showed the lowest survival (54.2 ± 4.17%) and molting rate (13.9 ± 10.5%). These findings indicate that G. fisheri at 0.32 kg/tank is the most effective shelter to enhance survival during the megalopa-to-first-crablet transition and may use to improved nursery production of S. paramamosain.