Ion flux and cortisol responses of cardinal tetra, Paracheirodon axelrodi (Schultz, 1956), to additives (tetracycline, tetracycline + salt or Amquel®) used during transportation: contributions to Amazonian ornamental fish trade

Summary The cardinal tetra, Paracheirodon axelrodi (Schultz), is the most important ornamental fish exported from Brazil and Colombia. During the transport of this species, Amazon fishermen usually add unmeasured amounts of tetracycline and/or table salt to the water in an effort to mitigate stress and mortality. The aim of the present study was to analyze the effect of salt, the antibiotic tetracycline and the ammonia chelating agent Amquel® in the transport of this species. Cardinal tetras were submitted to a 24-h boat transport in water containing either tetracycline hydrochloride (2.5 mg L−1), Amquel® (26.41 mg L−1), tetracycline + table salt (2.5 mg L−1 + 66.67 mg L−1), or additive-free water (control treatment). Whole-body cortisol measurements showed that fish transported with any water additive had lower cortisol levels compared to control. However, based on ionoregulatory and water quality parameters, the addition of tetracycline, Amquel® or the combination tetracycline + salt to the water of transport of cardinal tetras is not recommended when compared to control. Although Amquel® helped stabilize the pH and diminish total ammonia levels in the transport water, this compound dramatically increased net Na+ and Cl− uptake, and therefore compromised cardinal tetra ionoregulation.