The first direct measurements of ventilatory flow and oxygen utilization after exhaustive exercise and voluntary feeding in a teleost fish, Oncorhynchus mykiss

Abstract

A new “less invasive” device incorporating an ultrasonic flow probe and a divided chamber, but no stitching of membranes to the fish, was employed to make the first direct measurements of ventilatory flow rate (V̇w) and % O₂ utilization (%U) in juvenile rainbow trout (37 g, 8ºC) after exhaustive exercise (10-min chasing) and voluntary feeding (2.72% body mass ration). Under resting conditions, the allometrically scaled V̇w (300 ml kg⁻¹ min⁻¹ for a 37-g trout = 147 ml kg⁻¹ min⁻¹ for a 236-g trout exhibiting the same mass-specific O₂ consumption rate, ṀO₂) and the convection requirement for O₂ (CR = 4.13 L mmol⁻¹) were considerably lower, and the %U (67%) was considerably higher than in previous studies using surgically attached masks or the Fick principle. After exhaustive exercise, V̇w and ṀO₂ approximately doubled whereas frequency (fr) and %U barely changed, so increased ventilatory stroke volume (Vsv) was the most important contributor to increased ṀO₂. CR declined slightly. Values gradually returned to control conditions after 2–3 h. After voluntary feeding, short-term increases in V̇w, Vsv and ṀO₂ were comparable to those after exercise, and fr again did not change. However, %U increased so CR declined even more. The initial peaks in V̇w, Vsv and ṀO_2, similar to those after exercise, were likely influenced by the excitement and exercise component of voluntary feeding. However, in contrast to post-exercise fish, post-prandial fish exhibited second peaks in these same parameters at 1–3 h after feeding, and %U increased further, surpassing 85%, reflecting the true “specific dynamic action” response. We conclude that respiration in trout is much more efficient than previously believed.