# Integrating AIoT Technologies in Aquaculture: A Systematic Review
## 3 Components of AIoT in Aquaculture
### IoT Sensors
#### 3.1.1 Water Quality Monitoring Sensors  
Water quality monitoring sensors are fundamental to ensuring aquaculture systems' productivity and overall health, since they unremittingly track key parameters such as temperature, pH, salinity, dissolved oxygen, and ammonia. Studies [7; 38; 53] have observed the significant effect of these variables on the growth and physiological health of aquatic species, as even slight changes can cause stress, increase disease susceptibility, and in severe cases lead to mortality. Recent advancements in sensor technology have focused on improving precision, durability, and cost-effectiveness to meet the stringent monitoring requirements of aquaculture environments.  
For pH monitoring, ion-sensitive field-effect transistor (ISFET) and glass electrode sensors are widely used because of their high sensitivity to changes in water acidity--an essential factor in fish health [54]. While glass electrodes are commonly employed, they require frequent calibration and are susceptible to biofouling, limiting their long-term reliability in aquaculture applications [55]. On the other hand, ISFET sensors have improved durability and increased resistance to drift, which makes them better suited for prolonged use in aquatic environments. One study [55] demonstrated their effectiveness in long-term aquaculture surveillance, reinforcing their potential for improved water quality management.  
To maintain optimal water conditions, temperature sensors such as resistance temperature detectors (RTDs) and thermocouples are crucial, as fluctuations in temperature directly influence fish growth and metabolic rates. Similarly, dissolved oxygen (DO) sensors prevent hypoxic conditions, which can severely affect fish health. Traditional electrochemical DO sensors, including Clark electrodes, work via amperometric methods, but need regular preservation to prevent membrane fouling, a common problem in organically rich waters [37]. Optical dissolved oxygen (DO) sensors provide a more accurate and non-invasive solution by utilising the principle of fluorescence quenching caused by molecular oxygen [56]. However, as noted in [52], while optical sensors provide stable and accurate readings, they are more expensive and may degrade when exposed to specific waterborne chemicals. A comparative study in [57] revealed that even though conductive sensors  
Figure 2: Overview of AloT system components for aquaculture, illustrating data flow from environmental sensing to automated control.  
provide reliable salinity measurements, inductive sensors are more resilient for long-term use in aquaculture systems, where biofouling poses a persistent problem.  
Ammonia, a toxic metabolic by-product, must be carefully monitored to prevent harmful accumulations in aquaculture environments. The two primary methods for ammonia detection are ion-selective electrodes (ISEs) and colorimetric sensors. Though ISEs provide continuous and precise readings, they require frequent recalibration, since they are susceptible to sensor drift in fluctuating water conditions [58]. Colorimetric techniques are effective for ammonia detection, but have slower response times, making them less appropriate for real-time applications in high-density aquaculture settings [59].  
Although sensor technologies are essential for managing water quality, several challenges persist, including biofouling, sensor drift, and significant maintenance requirements, all of which can impact data accuracy and the sensors' durability [60]. To overcome these challenges, recent research has emphasised the creation of anti-bifouling coatings, the improvement of sensor materials, and the incorporation of multi-sensor systems. These advancements aim to improve data accuracy, minimise maintenance needs, and facilitate rapid detection of water quality changes.