Effect of submerged macrophytes planting mode on performance and economic profit of all-male adult Eriocheir sinensis culture

The mono-sex culture of adult Chinese mitten crab (Eriocheir sinensis) is a new culture mode, and Elodea nuttallii, Hydrilla verticillata and Vallisneria natans are common submerged macrophytes in the adult E. sinensis aquaculture ponds. We investigated the effects of four planting modes (Mode I, single planting of E. nuttallii; Mode II, single planting of H. verticillata; Mode III, mixed planting of E. nuttallii and H. verticillata in equal proportions; Mode IV, mixed planting of E.nuttallii, H. verticillata and V. natans in equal proportions) on the growth, gonadal development, culture performance and profitability of all-male E. sinensis. The results show that: 1) There was no significant difference in the body mass among the four planting modes, but Mode I group had significantly higher weight gain rate (WGR) and specific growth rate (SGR) than the other groups from September to October, and Mode II had the lowest WGR and SGR (P<0.05). 2) Among the Mode I–IV, no significant difference was found in the puberty molting rate, gonadosomatic index (GSI) and hepatosomatic index (HSI) of adult male E. sinensis (P>0.05), and at the end of August, the puberty molting rate was slightly higher in mixed planting of E. nuttallii and H. verticilla than in the single submerged macrophyte group, while Mode I group had slightly higher HSI and GSI than the other groups at mid-November (P>0.05), reaching about 7.8% and 3.3%, respectively. 3) As for the size distribution of adult males, Mode I group had the lowest percentage of larger-sized males (≥250 g) and the highest percentage of smaller-sized males (150–174.9 g and <150 g). The survival rate of all-male adult E. sinensis was significantly correlated to the planting modes of submerged macrophytes (P<0.05), and Mode II and Mode III groups had higher survival rates and yields but lower feed conversion rates. 4) For the economic assessment, Mode II and Mode III groups had higher feed input, and Mode II and Mode IV groups had higher input of aquatic plant. Besides, the total return, net profit and return-on-investment (ROI) were highest in Mode II group but lowest in Mode IV group. In conclusion, planting H. verticillata (Mode II) or mixed planting of E. nuttallii and H. verticillata (Mode III) can improve the culture performance and economic profit of all-male adult E. sinensis.