Influence of diel thermal variability on growth, development, swimming performance and stress response in salmonid fishes

Abstract

Accurately understanding the biological effects of temperature is important for effective species conservation, especially in this era of climate warming. Traditionally, temperature effects on fishes have been understood using fish held at stable temperatures. In many natural freshwater fish habitats, however, water temperature cycles daily. Diel thermal cycles can be as wide as 5-9 C in key salmonid habitats like the Miramichi River in New Brunswick. To date, little is known about the biological effects of diel thermal cycles on fishes. In my thesis, I investigated the growth, development, and swimming performance of Atlantic salmon (Salmo salar) under 16-21 and 19-24 C diel thermal cycles (representing cool and warm sites in the summer at the Miramichi). Additionally, I examined the stress response and post-angling survival of brook trout (Salvelinus fontinalis) after exposure to diel cycles with different daily thermal maximums (24, 26, or 27 C). I found that Atlantic salmon grew at similar rates at 16-21 and 19-24 C as parr, but smolts grew slower at 19-24 C especially for those from the relatively cooler Restigouche river compared to those from Miramichi. Atlantic salmon swimming efficiency was insensitive to acute warming or acclimation thermal cycle while sustainable swimming capacity stayed >90% (of the maximum) at the warmest test temperature (24 C) for both acclimation groups. Overall, Atlantic salmon appeared more resilient to warm temperatures than thought based on stable temperature experiments. Brook trout increased metabolic rate above resting levels after 26 or 27 C exposure which also increased some reflex impairments predicting greater postangling mortality. Tmax may be an important factor to consider in future closing/opening of recreational fisheries which currently considers some other water temperature parameter.