Net-chasing training improves the size homogeneous of freshwater prawn Macrobrachium rosenbergii reared at high stocking density through behavioral regulation

Abstract

Heterogeneous growth is a major concern for the intensive culture of prawns. Social interaction is believed to be one of the major contributions to the dispersed prawn size. We used net-chasing training to improve the size homogeneous of freshwater prawn Macrobrachium rosenbergii reared at high stocking density through the behavior regulation. Two stocking densities (low and high densities corresponding to 40 and 80 prawns m−2) and two training modes (no-chasing and 25%-exhausted net-chasing training) were applied. The prawns were cultured under four treatments (2 stocking densities × 2 training modes) using three replicates for 45 days. The fighting behavior, mortality and organ loss, and size heterogeneity were determined in a 9-day interval (on days 9, 18, 27, 36, and 45). The results showed that high stocking density induced an increase of fighting frequency and mortality with organ loss. The instantaneous mortality with organ loss was positively correlated with fighting frequency. The increased frequency of fighting and cannibalism induced by high density can be reduced by 25%-exhausted net-chasing training; however, the positive effects of net-chasing training on these behaviors were seen after 18 days of chasing. The size heterogeneity was increased at high stocking density, but can be further improved by at least 18 days of net-chasing training. The net-chased prawns reared at high density still showed obvious growth dispersion on days 9. These findings indicate that net-chasing training suppressed the behavior of fighting and cannibalism, producing a homogeneous prawn size at high density. The net-chased effects on the behavior and size heterogenous depended on the time of training, and long training periods (i.e., at least 18 days) should be employed when using net-chasing training to improve the heterogenous growth of prawns.