Introduction

In 2016, the national total output of aquatic products in China was 69 Mt, of which 32 Mt (46%) were freshwater aquatic products. The freshwater aquaculture area was 6.18
۱۰۵ ha, of which 2.76
۱۰۵ ha (44.71%) were freshwater fishponds. There is a huge increase in demand for freshwater aquatic products in China. However, the total aquaculture area is rapidly diminishing because of industry’s need for land. For example, the annual national decrease in total aquaculture area was 0.9% in 2015 and 1.4% in 2016 (Wang et al., 2017). To alleviate the situation, some intelligent systems which can contribute to increased production and reduced costs are being applied in freshwater aquaculture to monitor important water environmental variables in real time, such as dissolved oxygen (DO) concentration in water, water temperature, pH etc. (Simbeye & Yang, 2014; Simbeye, Zhao, & Yang, 2014). Siemens Corporation developed a system for monitoring 5 to 12 online water parameters in 2011 (Jawad, Nordin, Gharghan, Jawad, & Ismail, 2017). The American YSI Corporation also developed the YSI5200 aquaculture monitoring system for monitoring six kinds of water quality parameters in 2008. Researchers from the Chinese Academy of Fishery Sciences developed a multi-point online water quality testing system which can simultaneously monitor six water parameters in 2010. Scientists from Jiangsu University in China, developed a distribution monitoring system to determine a variety of key water parameters in real time, and the system had capacity for wireless data transmission in 2011 (Huan, Liu, & Chong, 2014; Huang et al., 2013). However, most of these existing monitoring systems, utilised in freshwater fishpond aquaculture, exchange information between the remote intelligent unit and monitoring computer through cable transmission. Cable communication systems carry many wires which results in a complex system and complications of data measurements and transmission. Moreover, such systems, once deployed, are inconvenient to expand to cover more targets. Further development of the freshwater fishpond aquaculture industry based on a cable communication system is limited, as cable communication systems are more suitable for a simple and small-scale scenario.