Oxytetracycline in intensive aquaculture: water quality during and after its administration, environmental fate, toxicity and bacterial resistance

Abstract

Oxytetracycline (OTC) is one of the most used antibiotics in aquaculture. This raises concerns due to its effects in human and animal health, the environmental contamination and the consequences arising therefrom. This review focuses on the OTC application in intensive aquaculture. It compiles and complements the dispersed information, presenting a comprehensive study about the OTC effects, from its administration to farmed fish, until its release into the surrounding aquatic systems. Several topics about OTC are presented and discussed: physicalchemical properties, interaction with ions, application to farmed fish, effects in water quality and possible treatments, biological activity and toxicity of OTC byproducts, environmental fate. Based on the information gathered, one concludes that OTC establishes strong complexes with Ca 2+ and Mg 2+ , which may have implications on its biological activity. OTC acts as inhibitor of protein synthesis and is poorly metabolized or unmetabolized by fish. Its common recommended daily dose is about 75 mg kg À1 but depends on the administration conditions and on target fish species. Regarding OTC removal from water within a semiclosed aquaculture's water circuit, ozonation and photodegradation are not completely efficient methods as none of them promotes total mineralization. However, photodegradation can be applied as a complementary method prior to ozonation, allowing to reduce costs. OTC by-products do not appear to retain its biological activity, but toxicity studies mimicking environmental conditions were not found. In open circuits (cages), water column where OTC is administered not suffer a specific treatment and the antibiotic is easily spread by the surrounding environments, affecting their inhabitants. OTC is released in the aquatic system in freely dissolved form and/or associated with organic or inorganic compounds, being subjected to natural photolysis, hydrolysis and/or biodegradation.

Antibiotics modulate biofilm formation in fish pathogenic isolates of atypical Aeromonas salmonicida

“…Furthermore, natural biofilms consist of many different species of bacteria and other organisms and the effects of being in such a diverse community on biofilm formation in the absence or presence of antibiotics remain unknown. Practically, sub‐MIC concentrations of antibiotics could be achieved in water or in the fish during and after therapeutic application in feed, as the agents could leach into the water (Xu & Rogers, 1994) or pass through the fish unmetabolised (Leal, Santos, & Esteves, 2019). This latter suggestion is of particular relevance in the culture of ballan wrasse, a stomachless species, as antibiotic dosing regimens used for this species are largely adapted from studies in salmonids that have grossly different gut physiology and longer gastrointestinal tracts for absorbing drugs (Le et al., 2019).…”

Effect of sunlight on the efficacy of commercial antibiotics used in agriculture

“…E. amylovora has dual growth modes -an epiphytic mode that is readily accessible for external antibiotics and an endophytic mode that is less accessible to external antibiotics [19]. In addition, tetracycline antibiotics including oxytetracycline are used in animal husbandry [20] and aquaculture [21]. Apart from the uses described above, data also suggests that antibiotics may find their way into and possibly persist in different animal and plant tissues [22][23][24], which could be an alternate pathway that can lead to the development of antibiotic-resistant bacteria.…”

“…antibiotics that are discussed here are available [21,[36][37][38][39][40][41][42]. However, to our knowledge, analysis such as the one we have conducted to monitor the efficacy of antibiotics subsequent to exposure to environmental elements are either lacking or not publicly available (as recognized by this article [14]).…”

Diphenyl diselenide‐loaded nanocapsules in silver catfish feed enhance growth, improve muscle antioxidant/oxidant status and increase selenium deposition: Advantages of nanotechnology for fish health

“…To meet the demand for human consumption of fish, semi‐intensive and intensive farming systems are frequently employed, resulting in more stressful conditions that cause losses and impair production (Leal, Santos, & Esteves, 2019). For these reasons, improving fish health is a substantial concern for fish producers.…”