Growth, survival and phenotypic expression of mud crab (Scylla serrata) under contrasting rearing systems

Implications for controlled breeding programme

Abstract

Aquaculture-based genetic improvement programmes depend on consistent phenotypic expression of economically important traits to accurately distinguish genetic variation from environmental noise. In mud crab (Scylla serrata) culture, widely used open production systems such as earthen ponds and floating cages are characterised by environmental fluctuations, social aggression and cannibalism, leading to highly variable growth and survival outcomes that constrain effective selective breeding. This study evaluated the growth performance, survival and phenotypic uniformity of S. serrata reared under three contrasting production environments in Kerala, India: habitat-structured recirculating aquaculture systems (HS-RAS), floating cage systems and conventional earthen ponds. Production data were obtained from biologically successful culture cycles and analysed as a comparative observational assessment of system-level performance. Crabs reared in HS-RAS exhibited significantly higher final body weight, average daily growth and survival compared with those reared in floating cages and earthen ponds (p < 0.05). Moreover, HS-RAS demonstrated reduced variability in growth traits, indicating greater phenotypic uniformity and biological stability. Floating cage systems showed intermediate performance, while earthen ponds exhibited the lowest growth, survival and consistency of trait expression. The superior performance of HS-RAS is attributed to enhanced environmental control and habitat structuring, which reduce stress, aggressive interactions and cannibalism. From a breeding perspective, the improved survival stability and reduced non-genetic variance observed in HS-RAS enhance the reliability of phenotypic records and minimise unintended selection caused by differential mortality. Although HS-RAS involve higher capital and operational costs, their capacity to support consistent phenotypic expression highlights their suitability as platforms for broodstock conditioning and the development of controlled selective breeding programmes in mud crab aquaculture.