Potential effects of social isolation on growth and morphotype development in juvenile male Macrobrachium rosenbergii

The giant freshwater prawn Macrobrachium rosenbergii exhibits a socially influenced male polymorphism, including individuals classified as small males (SM), orange-claw males (OC), and blue-claw males (BC) based on external characteristics, which contributes to variation in growth dynamics and population structure in aquaculture systems. This study evaluated the effects of complete social isolation on growth, survival, behavior, and morphotype-related traits, as well as growth responses following transfer to communal conditions. Juveniles reared in complete isolation in individual containers (406.9 mL) reached a significantly lower final weight (1.13 ± 0.29 g) than those maintained in communal culture (3.03 ± 1.19 g; P < 0.05), accompanied by reduced survival (72.5% vs. 93.33%), restricted behavioral expression, and a marked predominance of individuals classified as SM based on external morphotype-related characteristics (86.2%). In contrast, communal culture was associated with greater growth, higher survival, and a distribution dominated by individuals classified as OC based on external characteristics (60.71%). After 75 days of isolation, transfer to communal conditions was followed by a rapid increase in body weight, from 0.82 ± 0.57 g to 2.44 ± 0.77 g within 30 days, consistent with growth patterns resembling compensatory responses. These observations suggest that social interactions may influence growth dynamics and the development of phenotypic traits associated with morphotype differentiation in juvenile M. rosenbergii, and that growth patterns observed under isolation may remain responsive to environmental conditions following transfer to communal culture.