## 1 Introduction  
Aquaculture is a promising option to offer sustainable fish meat, and it will allow a considerable increase of fish consumption by 2050 [1]. It can be implemented under different conditions. Some facilities are deployed in the sea, while other facilities are placed inland. In inland facilities, fish are kept in tanks that can vary in size and materials. In facilities that perform intensive aquaculture, many efforts are taken to maximize the performance of the fish. Fish performance depends on different factors: environmental factors [2], production factors [3], and biotic factors [4]. In the facilities, it is possible to control some of those factors. Halogen lights are used over each tank to provide illumination to the tanks. With light, it is possible to change the photoperiod and modify the behavior of the fish to enhance their performance [5]. Moreover, filters can be used at the water entrance to eliminate the turbidity. Thus, the negative effects of turbidity are reduced, improving fish performance [6]. Other factors such as water temperature or water conductivity are not usually modified, although it is possible to modify them. Water temperature and conductivity can change the feeding needs of fish kept in the tanks [2]. Moreover, if fish are stressed their feeding consumption falls and the performance decreases. Many factors can cause stress on fish. There are many parameters that must be monitoredto help fish enhance their performance and therefore improve the sustainability and profitability of the fish farms. In recent years, the development of different Information and Communication Technologies (ICT) in conjunction with the creation of low-cost small sensors have made it possible to monitor many processes. Wireless sensor networks (WSN) are a clear example as they are often used for farming purposes. WSN have been used for monitoring the three vigor [7], greenhouses [8] and citrus crops [9]. Moreover, WSN are employed to monitor the state of farm animals such as goats [10] or cows [11]. Some systems have been proposed for monitoring fish farms [12; 13; 14; 15; 16; 17; 18; 19; 20; 21; 22]. They will be analyzed individually in the related work section. The majority of them are based on monitoring water quality including just a couple of water parameters to be monitored. Moreover, they usually employ commercial probes. The commercial probes for underwater monitoring have a high cost. Thus, if a WSN were to be utilized to monitor several parameters using commercial probes in all the production tanks, the cost of the system would be unaffordable for the fish farms. Moreover, other authors propose systems for monitoring fish behavior [23; 24; 25; 26; 27; 28; 29; 30]. In the related work section, we will analyze each proposal. Therefore, if we aspire to measure different parameters in fish farms facilities with WSN, it is crucial to reduce the cost of the sensors and include a wider variety of parameters in the same system. The aim of this paper is to design and deploy a low-cost WSN to monitor fish feeding process and water quality in aquaculture tanks. The system is composed of sensors that measure different parameters of the water quality (such as temperature, turbidity, or conductivity, among others), of the tank conditions (such as illumination and water level), and of the fish feeding behavior (such as swimming depth and velocity and fallen pellets). Moreover, the system has other sensors, such as the humidity sensor, that actuates as an emergency turn-off system to prevent damages caused by water in the node and other electronic circuits. In addition, presence sensors are placed in each tank to control the possible effects in fish behavior of the passage of the workers near the tanks. A total of three nodes control the different parameters in each tank. The nodes are wirelessly connected to an Access Point (AP) that sends the data to a server. The data is available on the local area network and on the Internet.