Influence of environmental temperatures on chemical restraint of Nile tilapia (Oreochromis niloticus) with propofol

Abstract

Background

Fish are ectothermic animals, so the water temperature determines their body temperature and directly influences their metabolism. In the anesthetic context, this must be considered, since the action and metabolism of medications may suffer interference if the temperature is outside the zone considered optimal for the species. Therefore, due to the influence of environmental temperature on fish metabolism, this study aimed to evaluate its effect on chemical restraint of adult Nile tilapia by immersion in 0.8 mg/L propofol.

Methods

Fifty animals were randomly divided into 2 groups. In group 1 (G1), the water temperature was kept below 20° C, while in second group (G2), it was above 25° C. After a general evaluation of the animals and the measurement of baseline parameters of posture, swimming pattern, and respiratory rate (RR), the tilapias were transferred to an induction aquarium containing the anesthetic diluted in water, where they remained for 5 minutes. Subsequently, they were transferred to a towel support for 15 minutes and monitored for heart rate (HR), RR, and spontaneous movement. Following this, the animals were transferred to a recovery aquarium.

Results

Propofol maintained stable heart rates and promoted absence of spontaneous movement, as well as reduced opercular movement rates in all evaluated tilapias. Statistical differences were observed between G1 and G2 in the HR and RR, with less spontaneous movement in G1.

Conclusions and clinical relevance

In conclusion, water temperature modifies the anesthesia response in Nile tilapias, with more pronounced effects observed at lower temperatures.