Interest and concern about rearing methods and their impact on animal welfare have increased. Production evaluation is population-based, and animal welfare analysis should be similar. In fish, the most common welfare indicators are gill state, fin damage, and body condition. The objective of this study was to evaluate the feeding rate effect on the welfare indicators of Oreochromis niloticus using an epidemiological approach. Five growth stages (from 1.2 to 360 g) were studied using four feeding rates as treatments: underfeeding (80%), recommended feeding (100%), and two levels of overfeeding (120% and 140%). The evaluated welfare indicators include the presence of lesions in different body areas and fins, the decrease in body condition index, and their impact on biomass production. Incidence and relative risk were determined for each indicator. Statistically significant associations were found in the indicators of mortality, weight, body condition (K), and presence of evident damage in the caudal and anal fin in all stages. The results showed that the feed rate directly affects the welfare indicators and production. Mortality, weight reduction, K reduction, and caudal and anal fin damage incidence showed to be relevant indicators in all O. niloticus growing stages. As a result of this study, the epidemiological approach seems to be a valuable tool for production. A risk traffic light method is a proposal that could have great potential, with the suggested limits for WI's concerning the individuals present in the culture pond, allowing progressive evaluation and decision-making to correct risky situations.

In farming, sustainability together with food safety is one of the main objectives to be achieved. Aquaponics is a technique that combines aquatic animals, such as fish, with the hydroponic production of plants that function as biological filters. The proper functioning of the system is based on the dynamic balance of the elements that make it up. Several studies confer aquatic macrophytes such as L. minor, great attributes, highlighting their use for feeding different species. Unfortunately, there is very little information on the system management of macrophytes in aquaponics. To determine the appropriate management parameters for the cultivation of L. minor integrated into the production of Oreochromis niloticus, in aquaponics, three experiments were carried out to evaluate the effect of the hydraulic retention time (HRT), the planting density, plant dissemination and the balance of nutrients in the systems. The results show that the highest biomass production and plant growth are achieved with high flow rates and short HRTs. Planting density has a direct effect on the behaviour of the plant. Regarding the balanced budget, between 7% and 8% of the nutrients (input in dry matter, N and P) are retained by L. minor, keeping the water quality within adequate limits for tilapia production.