Oxygen consumption of the dog snapper in captivity: implications of water quality and fish stage

Respirometry represents the least invasive method to investigate fish physiology. Therefore, oxygen consumption (OC) of the dog snapper Lutjanus jocu was evaluated in two specific culture water conditions: the cleanest possible water, and accumulated nitrate water. Clean water represents the seawater collected straight from the environment with a basic treatment, and nitrate water represents the seawater kept at the rearing tanks using advanced water treatment in its recirculating system, in which nitrogen compounds accumulate. Fish were classified into stages, and median OC for juvenile, grow-out and broodstock stages were 322.4, 176.5 and 78.4 mg·(kg·h)-1, respectively. Despite no significant differences in OC for the dog snapper were found during day and nighttime, this last condition represents a 5% increase on the measurements, possibly related to the circadian rhythm of this species, known for being active during the night. Remarkable increase in respirometry is observed in the dog snapper grow-out stage cultured in nitrate water. This condition demands extra management of the production to promote fish welfare, and consequently better growth.