We investigated the effects of plant density on the welfare of African catfish, Clarias gariepinus, in coupled aquaponics over 85 days. The moderate density (mpd) of basil, Ocimum basilicum, was compared with the high density (hpd) and control (n = 0). The behavior was analyzed by visual and video observations, and after the application of induced stressors, skin injuries, blood glucose, lactate, and plasma cortisol responses were considered. The hpd fish showed the least activity (control: visual 77.8%, video 81.6%; mpd: 74.6%, 82.6%; hpd: 63.2% [p < 0.05], 78.8%). High agonistic behavior (control: 5, 131; mpd: 4, 57; hpd: 1, 45) and the highest number of injuries (control: 3.9; mpd: 2.9; hpd: 3.4) were observed in the control. Glucose and lactate levels did not differ significantly (control: 5.5, 2.6 mmol/L; mpd: 5.6, 2.7 mmol/L; hpd: 5.3, 2.6 mmol/L); however, cortisol levels did (control: 18.8 ng/mL, mpd: 19.9 ng/mL, hpd: 25.8 ng/mL). pH adjustment led to additional stress, resulting in temporal cortisol alterations. While in the control and mpd, low cortisol levels were followed by acute responses and downregulation, the hpd fish showed prior elevation and lagged an acute response. However, comparing injuries and behavioral patterns with control, aquaponics with high basil density influenced African catfish positively.

The aquaculture sector has been the key factor in meeting the growing demand for high-quality food by contributing significantly to the global fish production. The portion of fishmeal in aqua feeds has been decreased significantly in recent years, however, increased production in aquaculture still led to demands of fishmeal that cannot be covered by sustainably caught small pelagic fish. Hence, alternatives for fishmeal in aqua feeds are an inevitable necessity. Different plant proteins have been evaluated in the past and rapeseed proteins are considered valuable protein sources for fishmeal-free aqua feeds. Rapeseed is highly available on a global scale and provides one of the most balanced amino acid composition among plant-based protein sources. Additionally, rapeseed cultivation is characterised by low production costs, ecological and economic benefits in cerealdominated agriculture and provision of two highly nutritive products. Subsequently, rapeseed proteins have been intensely investigated over the past decades and knowledge of the application of these proteins in diets for different species of fish has improved dramatically. However, there is no adequate complete review for the application of rapeseed proteins in aqua feeds. This review outlines and discusses the relevant factors influencing the inclusion of rapeseed proteins as fishmeal alternatives in fish diets and highlights provisional thresholds for anti-nutritive substances as well as future research needs.

Optimizing production in aquaponics requires in‐depth knowledge of the plant, fish and microbial compartments. This opinion paper is focused on root‐released organic compounds and their implication in aquaponics, an area that has received little to no direct research to date. Key scientific literature from two distinct fields of study—phytochemicals in aquaculture science and root exudates in plant science—reveals possible pathways and effects. Root exudates, passively or actively released by plants as a stress response, protection or signalling, have the potential to influence the systems microbiome and the cultured fish, as similar phytochemicals have been found to affect bacterial abundance and diversity and fish health and behaviour. These are key aspects to run aquaponics successfully, which shows the need for further investigation to better understand sources and mechanisms of such molecules and possible ways to harness beneficial effects that can guide new research directions as the role of aquaponics grows in recirculating aquaculture.

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