Effect of different harvesting techniques on the production and population structure of Macrobrachium rosenbergii in a wetland ecosystem of South India

Culling prior to final harvest has shown many advantages in improving the marketable yield in freshwater prawn farming. This study is an attempt to compare three harvesting techniques on the production and population structure of Macrobrachium rosenbergii farming in a wetland ecosystem of South India. The study also compares the marketable yield structure and economics of farming of these prawns in three quadruplicate sets of polders following either complete harvest (T1) or traditional partial harvest through dewatering and cast netting (T2) or a modified cull harvest (T3) with a newly designed drag seine. Results showed better yield and faster morphotype transformation among treatments that followed cull harvesting. Among them, better results on mean weight and survival rate (64 g and 54% respectively) were recorded from T3. The results also showed that irrespective of the type of cull harvesting, their inclusion in polders facilitated faster morphotypic transformation and thenceforth the preponderance of terminal morphotypes in the harvested population. Likewise, larger sized male morphotypes were significantly higher (35% and 25% respectively) in T2 and T3. The net production also varied significantly within the treatments from 140 kg ha^?1 in T1 to 515 kg ha^?1 in T3. From a marketability point of view also, the total marketable prawns (>50 g group) varied considerably from 94% (T2) and 92% (T3) to 78% in T1. While working out the harvest economics through benefit–cost analysis, it was inferred that the introduction of the new harvest technique was more profitable compared to the traditional systems prevailing in Kuttanad. This study also emphasizes the need for resorting to modified partial harvesting through the use of drag seines, as it considerably reduces the cost on harvesting in a waterlogged ecosystem such as Kuttanad.