Impact of phased harvesting on population structure, feed intake pattern and growth performance of Macrobrachium rosenbergii DeMan (giant freshwater prawn) in polyculture with carps in concurrent rice–fish culture

Abstract

This study was carried out to study the impact of phased harvesting on the population structure, feed intake pattern and growth performance of Macrobrachium rosenbergii in polyculture with carps in a deepwater rice–fish system. There were two experimental conditions—rice–fish culture with phased harvesting (T1) and rice–fish culture without phased harvesting (T2)— and a control, which consisted of rice monoculture without fish (T3). In the T1 trial, 61% of the population had a mean body weight (MBW) <20 g 120 days after stocking (DAS), which fell significantly to 7.3% at 210 DAS. However, in the T2 trial, 62% of the population had a MBW <20 g at 120 DAS, which only fell to 23.7% at 210 DAS. Similarly, at 210 DAS, 12.5% of the population attained a MBW > 80 g in the T1 trial, while none of the population reached a MBW > 80 g in the T2 trial. The removal of fast-growing individuals in T1 improved the prospects of other smaller individuals to achieve their individual growth potential. This step also disrupted the continuation of the socially induced differential growth rates, resulting in a wide variation in size within the population over time. The matrix of dietary overlap(s) of cultured species revealed that the degree of food preference was more similar between Cyprinus carpio and M. rosenbergii (0.9), while it overlapped poorly between Catla catla and M. rosenbergii (0.42). This high similarity index between bottom dwellers is evidence of the strong possibility that these bottom dweller compete for food. Natural and supplemental feed together with phased harvesting boosted the production of freshwater prawns (550 kg/ha) in the T1 trial, while a 11.3% reduction in production was recorded in the T2 trial.