Morphological Changes in Gill Epithelia of Heat-Stressed Rainbow Trout, Salmo gairdneri: Evidence in Support of a Temperature-Induced Surface Area Change Hypothesis

Abstract

Surface morphology of the gill structure of hatchery-reared rainbow trout (Salmo gairdneri) exposed to heat shock was examined by scanning electron microscopy. Changes were greatest in fish previously acclimated to 6 °C and exposed to 24 or 30 °C water for 3–5 d. Gill epithelia of heat-stressed fish showed a reduction and loss of the microridge patterns. The surface of the efferent arterial sides of the primary lamellae became irregular and rugose, and fusion of the secondary lamellae occurred at higher temperatures. The morphological changes along with an increase in mucus production may be a major factor in causing hypoxia in heat-stressed fish.Key words: gill epithelium, rainbow trout, primary lamellae, secondary lamellae, temperature, heat stress, scanning electron microscopy